0000950170-24-027594 | 10-K | XBRL Viewer

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Common Stock - Additional Information (Details)	1 Months Ended			2 Months Ended	12 Months Ended
Common Stock - Additional Information (Details)	Aug. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) $ / shares shares	May 31, 2022 USD ($) $ / shares shares	Mar. 07, 2024 USD ($) shares	Dec. 31, 2023 USD ($) Vote shares	Dec. 31, 2022 USD ($) $ / shares shares	May 24, 2022 $ / shares
Class of Stock [Line Items]
Number of votes per share \| Vote					1
Dividends declared					$ 0	$ 0
Additional common stock reserved for issuance \| shares		10,338,814			11,556,789	10,338,814
Beneficial ownership limitation, minimum percentage of shares outstanding			9.99%
Beneficial ownership limitation, maximum percentage of shares outstanding			19.99%
ATM Sales Agreement
Class of Stock [Line Items]
Net proceeds received after deducting underwriting discounts and commissions and other offering related costs					$ 0	$ 4,978,000
Shares issued during period value						$ 4,978,000
Maximum aggregate offering price of common stock	$ 150,000,000
ATM Sales Agreement \| Sales Agreement
Class of Stock [Line Items]
Shares issued during period \| shares					0	209,349
Net proceeds received after deducting underwriting discounts and commissions and other offering related costs						$ 5,000,000
ATM Sales Agreement \| Sales Agreement \| Subsequent Event
Class of Stock [Line Items]
Shares issued during period \| shares				365,316
Net proceeds received after deducting underwriting discounts and commissions and other offering related costs				$ 9,200,000
2022 Public Offering
Class of Stock [Line Items]
Shares issued during period \| shares		4,338,104
Net proceeds received after deducting underwriting discounts and commissions and other offering related costs		$ 75,000,000
Shares issued, price per share \| $ / shares		$ 18.5				$ 18.5
2022 Public Offering \| Underwriters
Class of Stock [Line Items]
Shares issued during period \| shares		284,049
Maximum \| ATM Sales Agreement
Class of Stock [Line Items]
Shares issued during period value	450,000,000
Common stock available for future issuance of shares					$ 150,000,000
Maximum \| ATM Sales Agreement \| Sales Agreement \| Subsequent Event
Class of Stock [Line Items]
Common stock available for future issuance of shares				$ 140,600,000
Pre-funded Warrants
Class of Stock [Line Items]
Number of warrants to purchase \| shares			4,000,000
Exercise price per warrant share \| $ / shares			$ 0.0001
Purchase price per warrant \| $ / shares			$ 12.4999
Net proceeds from issuance of pre-funded warrants			$ 49,800,000
Offering expenses			$ 200,000
Common Stock
Class of Stock [Line Items]
Closing Price Per Share \| $ / shares							$ 12.5
Common Stock \| ATM Sales Agreement
Class of Stock [Line Items]
Shares issued during period \| shares						209,349
Common Stock \| Maximum \| ATM Sales Agreement \| Sales Agreement
Class of Stock [Line Items]
Shares issued during period value	$ 150,000,000

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	At The Market	Public Offering	Common Stock	Common Stock At The Market	Common Stock Public Offering	Additional Paid-In Capital	Additional Paid-In Capital At The Market	Additional Paid-In Capital Public Offering	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2021	$ 186,380			$ 3			$ 470,629			$ (284,046)	$ (206)
Beginning balance, shares at Dec. 31, 2021				29,555,119
Proceeds from sale of pre-funded warrants in private placement, net of issuance costs	49,785						49,785
Issuance of common stock from of net issuance costs		$ 4,978	$ 75,025					$ 4,978	$ 75,025
Issuance of common stock from net of issuance costs, shares					209,349	4,338,104
Issuances of common stock from employee stock plans	1,392						1,392
Issuances of common stock from employee stock plans, shares				151,742
Stock-based compensation	11,264						11,264
Foreign currency translation gain (loss)	627										627
Unrealized loss on marketable securities	(447)										(447)
Net loss	(83,838)									(83,838)
Ending balance at Dec. 31, 2022	$ 245,166			$ 3			613,073			(367,884)	(26)
Ending balance, shares at Dec. 31, 2022	34,254,314			34,254,314
Issuances of common stock from employee stock plans	$ 1,447						1,447
Issuances of common stock from employee stock plans, shares				143,998
Stock-based compensation	17,091						17,091
Foreign currency translation gain (loss)	(655)										(655)
Unrealized loss on marketable securities	784										784
Net loss	(116,798)									(116,798)
Ending balance at Dec. 31, 2023	$ 147,035			$ 3			$ 631,611			$ (484,682)	$ 103
Ending balance, shares at Dec. 31, 2023	34,398,312			34,398,312

Common Stock

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Common Stock

8. Common Stock

The holders of the Company’s common stock have one vote for each share of common stock held by them. Holders of shares of the Company’s common stock are entitled to dividends when, as and if declared by the board of directors. No dividends had been declared as of December 31, 2023 or December 31, 2022.

The Company had reserved the following shares of common stock, on an as-converted basis, for future issuance as follows:


	Year Ended December 31,
	2023		2022
Options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan		4,099,947		2,993,280
Restricted stock units issued and outstanding under the 2019 Equity Incentive Plan		13,500		27,000
Options available for future grants		3,032,820		2,820,341
Pre-funded warrants issued and outstanding		4,000,000		4,000,000
Shares reserved under the 2019 Employee Stock Purchase Plan		410,522		498,193
Total		11,556,789		10,338,814

In August 2023, the Company filed a shelf registration statement on Form S-3 with the SEC, which was later declared effective, related to the sale and issuance of up to $450 million of the Company’s securities, including up to $150 million of shares of common stock that may be offered and sold from time to time in one or more “at-the-market” offerings pursuant to a Controlled Equity OfferingSM Sales Agreement (the “ATM Sales Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) and Leerink Partners LLC. The ATM Sales Agreement replaced the Controlled Equity OfferingSM Sales Agreement, entered in November 2020, with Cantor and Stifel, Nicolaus & Company, Incorporated (the “Prior ATM Sales Agreement”). The ATM Sales Agreement provides for the sale and issuance of shares of common stock having an aggregate offering price of up to $150.0 million. As of December 31, 2023, there were up to $150 million of shares of common stock available for future issuance under the ATM Sales Agreement. No shares were sold under the ATM Sales Agreement or the Prior ATM Sales Agreement during the year ended December 31, 2023. During the year ended December 31, 2022, the Company sold 209,349 shares of common stock in “at the market” offerings pursuant to the Prior ATM Sales Agreement, for net proceeds of $5.0 million, after deducting commissions and other offering related costs. During the period from January 1, 2024 through the date of filing of this Annual Report on Form 10-K, the Company sold 365,316 shares of common stock in “at the market” offerings pursuant to the ATM Sales Agreement, for net proceeds of $9.2 million, after deducting commissions and other offering related costs. As of the date of filing of this report there were up to $140.6 million shares of common stock available for future issuance under the ATM Sales Agreement.

In December 2022, the Company completed an underwritten public offering (“2022 Public Offering”) of 4,338,104 shares of common stock, including 284,049 shares of common stock issued in connection with the exercise of the over-allotment option by the underwriters, at a public offering price of $18.50 per share. The Company received approximately $75.0 million in net proceeds from the 2022 Public Offering, after deducting underwriting discounts and other offering-related costs.

In May 2022, through a private placement financing, the Company issued pre-funded warrants to purchase an aggregate of 4,000,000 shares of the Company’s common stock. Each pre-funded warrant has an exercise price of $0.0001 per share. The purchase price per pre-funded warrant was $12.4999 (representing the $12.50 per share closing price of the common stock on May 24, 2022, less the exercise price of $0.0001 per pre-funded warrant). The private placement financing of the pre-funded warrants resulted in net proceeds of $49.8 million, after deducting $0.2 million of offering expenses. As of December 31, 2023, all the pre-funded warrants issued in the private placement were outstanding.

The pre-funded warrants provide that the holder will not have the right to exercise any portion of the pre-funded warrants if such holder, together with its affiliates, would beneficially own in excess of 9.99% of the number of shares of the Company's common stock outstanding immediately after giving effect to such exercise (the “Beneficial Ownership Limitation”); provided, however, that the holder may increase or decrease the Beneficial Ownership Limitation by giving 61 days’ notice to the Company, but not to any percentage in excess of 19.99%.

The pre-funded warrants were classified as a component of permanent equity in the Company’s consolidated balance sheet as they are freestanding financial instruments that are immediately exercisable, do not embody an obligation for the Company to repurchase its shares and permit the holders to receive a fixed number of shares of common stock upon exercise.

- Definition

The entire disclosure for equity.

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+ Details

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Total property and equipment	$ 11,815	$ 10,788
Less accumulated depreciation and amortization	(9,367)	(8,249)
Property and equipment, net	2,448	2,539
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	7,399	6,558
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	3,295	3,295
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	727	578
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	$ 394	$ 357

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 17,091	$ 11,264
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	7,941	5,206
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 9,150	$ 6,058

Net Loss Per Share Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Pre-funded warrants to purchase common stock	4,000,000	4,000,000

Commitments - Summary of Balance Sheet Classification of Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Operating lease right-of-use assets	$ 5,228	$ 6,940
Operating lease liabilities, current	2,448	2,171
Operating lease liabilities, non-current	4,458	$ 6,819
Total operating lease liabilities	$ 6,906

Stock-Based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

9. Stock-Based Compensation

Stock Option Plan

In 2015, the Company adopted the FLX Bio, Inc. 2015 Stock Plan (the “2015 Plan”).

In November 2019, the Company’s board of directors adopted the 2019 Equity Incentive Plan (the “2019 Plan” and collectively with the 2015 Plan, the “Option Plans”). Upon the effectiveness of the 2019 Plan, the 2015 Plan terminated and no further grants may be made thereunder. However, the 2015 Plan will continue to govern the terms and conditions of the outstanding awards previously granted thereunder. As of December 31, 2023, the Company had 3,032,820 shares of common stock available for grant under the Option Plans. In addition, the number of shares reserved for issuance under the 2019 Plan automatically increases on January 1 of each year beginning January 1, 2020 by a number equal to (i) 4% of the shares of common stock outstanding on the last business day of the prior fiscal year or (ii) the number of shares determined by the Company’s board of directors.

The Option Plans provide for the granting of incentive and non-statutory stock options and restricted shares of common stock options to eligible employees, officers, directors, advisors and consultants. Terms of the stock option agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the Options Plans. Options granted generally vest over four years and expire no later than ten years from the date of grant. As a private company, the estimated fair value of the Company’s underlying common stock was determined by the board of directors. The fair value of the Company’s common stock is based on the closing price of its common stock on the date of grant. As of January 1, 2023, an additional 1,370,173 shares of common stock were reserved for issuance pursuant to the automatic increase to the authorized shares under the 2019 Plan.

Employee Stock Purchase Plan

In October 2019, the Company adopted the 2019 Employee Stock Purchase Plan (the “2019 ESPP”). The Company reserved 240,336 shares of common stock pursuant to purchase rights to be granted to the Company’s employees. The 2019 ESPP provides that the number of shares reserved and available for issuance automatically increases on January 1 of each calendar year, beginning January 1, 2020, by the lesser of (1) 1.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (2) 240,336 shares or (3) a number determined by the board of

directors that is less than (1) and (2). As of January 1, 2023, no additional shares of common stock were authorized for issuance pursuant to the annual automatic increase to the authorized shares under the 2019 ESPP.

Under the 2019 ESPP, eligible employees are granted rights to purchase shares of common stock, which can be funded through payroll deductions that cannot exceed 15% of each employee’s compensation. The 2019 ESPP generally provides for a 24-month offering period, which includes four six-month purchase periods. At the end of each purchase period, eligible employees are permitted to purchase shares of common stock at 85% of the lower of fair market value at the beginning of the offering period or fair market value at the end of the purchase period. During the years ended December 31, 2023 and 2022, employees purchased 87,671 shares at weighted average price of $12.34 and 59,066 shares at a weighted average exercise price of $12.86, respectively. The 2019 ESPP is considered a compensatory plan and the Company recorded stock-based compensation expense of $1.3 million and $0.9 million for the years ended December 31, 2023 and 2022, respectively.

Stock Options

Stock option activity under the 2019 Plan is set forth below for the year ended December 31, 2023:


				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Shares			Price Per		Term		Value
	Outstanding			Share		(Years)		(in thousands)
Balances at December 31, 2022		2,993,280		$	18.95		7.9	$	9,425
Stock options granted		1,218,608			25.61
Stock options exercised		(51,027	)		9.45
Stock options cancelled		(60,914	)		22.23
Balances at December 31, 2023		4,099,947		$	21.00		7.6	$	23,206
Vested and expected to vest at December 31, 2023		4,099,947			21.00		7.6	$	23,206
Exercisable at December 31, 2023		2,366,831			19.27	6.8		$	17,598

The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the underlying awards and the quoted price of the Company’s common stock for options that were in-the-money as of December 31, 2023.

The options granted in the years ended December 31, 2023 and 2022 had a weighted average per share grant-date fair value of $20.20 and $14.82, respectively, and a total grant date fair value of $24.6 million and $16.8 million, respectively.

The aggregate intrinsic value of stock options exercised in the years ended December 31, 2023 and 2022 was $0.7 million and $1.3 million, respectively. Cash received from stock option exercises were $0.5 million and $0.7 million for the years ended December 31, 2023 and 2022, respectively. The Company issues new shares of common stock upon exercise of options. In connection with these exercises, there was no tax benefit realized by the Company due to its current loss position.

The aggregate fair value of options that vested in the years ended December 31, 2023 and 2022 was $15.2 million and $9.7 million, respectively.

Restricted Stock Units

Restricted Stock Units (“RSU”) activity under the 2019 Plan is set forth below for the year ended December 31, 2023:


				Weighted
				Average
	Number of			Grant Date
	Shares			Fair Value
	Outstanding			Per Share
Balances at December 31, 2022		27,000		$	44.66
RSUs granted		—			—
RSUs vested and settled		(13,500	)		44.66
RSUs forfeited		—			—
Balances at December 31, 2023		13,500		$	44.66

Employee stock option valuation

In determining the fair value of the options granted, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine.

Expected term

The expected term represents the period that the Company’s options granted are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term). The Company has very limited historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock option grants.

Expected volatility

Since the Company recently became a public company and has only a limited trading history for its common stock, the expected volatility was estimated based on the average historical volatility for comparable publicly traded biopharmaceutical companies and our historical volatility over a period, where available, equal to the expected term of the stock option grants. The comparable companies were chosen based on their similar size, life cycle stage or area of specialty.

Risk-free interest rate

The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of the options.

Expected dividend

The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

The assumptions used to value employee and non-employee stock option awards granted under the Option Plans during the years ended December 31, 2023 and 2022, using the Black-Scholes option pricing model, were as follows:


	For the Year Ended December 31,
	2023	2022
Fair value	$11.25 - $23.70	$10.35 - $28.63
Expected term (in years)	5.87 - 6.06	5.79 - 6.08
Volatility	94.9% - 97.8%	89.8% - 94.3%
Risk-free interest rate	3.46% - 4.71%	1.42% - 4.09%
Dividend yield	—	—

Employee stock purchase plan

The fair value of the rights granted to employees under the 2019 ESPP was estimated using a Black-Scholes option-pricing model with the following valuation assumptions:


	For the Year Ended December 31,
	2023	2022
Fair value	$4.79 - $12.12	$6.53 - $14.89
Expected term (in years)	0.50 - 2.00	0.50 - 2.00
Volatility	64.3% - 93.2%	91.0% - 101.5%
Risk-free interest rate	4.14% - 5.51%	1.49% - 4.75%
Dividend yield	—	—

Stock-based compensation expense

Total stock-based compensation expense recognized for stock options and RSUs granted to both employees and non-employees and for the employee stock purchase plan was as follows (in thousands):


	For the Year Ended December 31,
	2023		2022
Research and development	$	7,941	$	5,206
General and administrative		9,150		6,058
Total stock-based compensation expense	$	17,091	$	11,264

As of December 31, 2023, unrecognized stock-based compensation cost related to outstanding unvested stock options and RSUs that are expected to vest was $29.2 million. This unrecognized stock-based compensation cost is expected to be recognized over 2.6 years.

Stock-Based Compensation - Summary of Assumptions Used to Value Under Stock Option Plans (Details) - Employee and Non-employees - Share-based Payment Arrangement, Option - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility, minimum	64.30%	91.00%
Volatility, maximum	93.20%	101.50%
Risk-free interest rate, minimum	4.14%	1.49%
Risk-free interest rate, maximum	5.51%	4.75%
Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility, minimum	94.90%	89.80%
Volatility, maximum	97.80%	94.30%
Risk-free interest rate, minimum	3.46%	1.42%
Risk-free interest rate, maximum	4.71%	4.09%
Minimum \| 2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value	$ 4.79	$ 6.53
Expected term (in years)	6 months	6 months
Minimum \| Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value	$ 11.25	$ 10.35
Expected term (in years)	5 years 10 months 13 days	5 years 9 months 14 days
Maximum \| 2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value	$ 12.12	$ 14.89
Expected term (in years)	2 years	2 years
Maximum \| Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value	$ 23.7	$ 28.63
Expected term (in years)	6 years 21 days	6 years 29 days

Commitments (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Summary of Maturities of Lease Liabilities

The following table summarizes maturities of operating lease liabilities as of December 31, 2023 (in thousands):


2024	$	2,855
2025		2,662
2026		2,137
Thereafter		—
Total future undiscounted lease payments		7,654
Less: Imputed interest		(748	)
Total lease liabilities	$	6,906

Summary of Supplemental Balance Sheet Information Related Operating leases

The following table summarizes the supplemental balance sheet information related to operating leases at December 31, 2023 (in thousands):


Operating leases
Operating lease right-of-use assets	$	5,228

Operating lease liabilities, current		2,448
Operating lease liabilities, non-current		4,458
Total operating lease liabilities	$	6,906

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and include the consolidated accounts of the Company and its wholly-owned subsidiary, RAPT Therapeutics Australia Pty Ltd., which was established in 2018 and deregistered during the quarter ended June 30, 2023. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its critical accounting policies or estimates related to revenue recognition, clinical trial accruals, fair value of assets and liabilities and stock-based compensation. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s balance sheets and the amounts of expenses and revenue reported for each of the periods presented are affected by estimates and assumptions. Actual results could differ from such estimates or assumptions. Concentration of Credit Risk and Other Risks and Uncertainties The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products and protection of proprietary technology. If the Company does not successfully obtain regulatory approval, commercialize or partner any of its product candidates, it will be unable to generate revenue from product sales or achieve profitability. Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and marketable securities. Substantially all the Company’s cash is held by two financial institutions. Such deposits may, at times, exceed federally insured limits. The Company invests its cash equivalents in highly rated money market funds and short-term marketable securities comprising commercial paper, corporate bonds and U.S. government agency securities. Segments The Company operates as a single operating segment. The Company’s chief operating decision maker, its President and Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources, making operating decisions and evaluating financial performance. Fair Value of Financial Instruments The carrying amount of the Company’s financial instruments, including certain prepaid and accrued expenses, approximates fair value due to their short-term maturities. Cash Equivalents The Company considers all highly liquid investments with original maturities of 90 days or less from the date of purchase to be cash equivalents. Marketable Securities Marketable securities primarily consist of commercial paper, corporate debt securities and U.S. government agency securities. The Company has classified its marketable securities as available-for-sale and may sell these securities prior to their stated maturities. The Company views these marketable securities as available to support current operations and classifies marketable securities with maturities beyond 12 months as current assets. The Company’s marketable securities are carried at estimated fair value, which is derived from independent pricing sources based on quoted prices in active markets for similar securities. Unrealized gains and losses are reported as a component of accumulated other comprehensive income (loss). The cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in other income, net on the consolidated statements of operations. All of the Company's available-for-sale investments are subject to a periodic impairment review. For each available-for-sale investment whose fair value is below its amortized cost, the Company determines if the impairment is a result of a credit-related loss or other factors using both quantitative and qualitative factors, including the length of time and extent to which the market value has been less than amortized cost, the financial condition and near-term prospects of the issuer and the Company’s intent and ability to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in market value. If the impairment is a result of a credit-related loss, the Company recognizes an allowance for credit losses. If the impairment is not a result of a credit loss, the Company recognizes the loss in other comprehensive loss. Property and Equipment Property and equipment consist of computer equipment, laboratory equipment, leasehold improvements and furniture and fixtures, and is recorded at cost, less accumulated depreciation and amortization. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the improvements. Depreciation and amortization begin at the time the asset is placed in service. Maintenance and repairs are charged to expense as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in the results of operations. Impairment of Long-Lived Assets The Company evaluates its long-lived assets for impairment annually or more frequently whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparing the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. For the years ended December 31, 2023 and 2022, the Company did not record any impairment losses on long-lived assets. Leases The Company adopted ASU No. 2016-02, Leases (Topic 842) on January 1, 2022 using the modified retrospective approach. The Company elected to apply the modified retrospective approach that allowed it to continue applying the guidance in effect, at the time of adoption, in the comparative periods presented in the Consolidated Balance Sheets and recognize a cumulative-effect adjustment to the opening balance of accumulated deficit on the date of adoption. The Company elected the package of practical expedients, which permits it not to reassess under the new standard the prior conclusions about lease identification, lease classification and initial direct costs. The Company also elected to combine lease components (for example, fixed rent payments) with non-lease components (for example, common-area maintenance costs) on the facilities asset class. Lastly, the Company elected the short-term lease practical expedients allowed under the standard and the practical expedient to use hindsight in determining the lease term for all its operating leases. At inception of a contract, the Company determines whether an arrangement is or contains a lease. For all leases, the Company determines the classification as either operating leases or financing leases. Operating leases are included in operating lease right-of-use (“ROU”) assets and operating lease liabilities in the Company’s consolidated balance sheets. Lease recognition occurs at the commencement date and lease liability amounts are based on the present value of lease payments over the lease term. The lease term may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. The Company uses an implicit rate when readily available, or its incremental borrowing rate based on the information available at lease commencement date, in determining the present value of lease payments. ROU assets represent the Company's right to use underlying assets for the lease term and operating lease liabilities represent the Company's obligation to make lease payments under the lease. ROU assets also include any lease payments made prior to the commencement date and exclude lease incentives received. Operating lease expense is recognized on a straight-line basis over the lease term. Lease agreements with both lease and nonlease components are generally accounted for together as a single lease component. Revenue License and collaborative agreements revenue consists of license, milestone and royalty payments generated through agreements with strategic partners for the development and commercialization of certain product candidates. The terms of an agreement may include a non-refundable upfront fee, payments based upon achievement of milestones and royalties on net product sales. If a portion of the nonrefundable upfront fee or other payments received is allocated to continuing performance obligations under the terms of an agreement, such portion is recorded as deferred revenue and recognized as revenue when or as the underlying performance obligation is satisfied. The Company recognizes revenue when it transfers promised goods or services to customers or counterparties in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized, the Company performs the following steps: (i) identification of the promised goods or services in the agreement; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the agreement; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to performance obligations based on estimated selling prices; and (v) recognition of revenue when or as the Company satisfies each performance obligation. Licenses: If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in an agreement, the Company will recognize revenue from the nonrefundable, upfront fee allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. If a license is bundled with other performance obligations, the Company utilizes judgment to assess the nature of the combined performance obligations to determine whether the combined performance obligations are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: If an agreement includes event-based or milestone payments, the Company evaluates whether the events or milestones are considered likely to be achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is unlikely that a significant revenue reversal of cumulative revenue recognized would occur, the value of the associated event-based or milestone payments is included in the transaction price. Event-based or milestone payments that are not within the control of the Company are not included in the transaction price until they become likely to be achieved. Royalties: If an agreement includes sales-based royalties and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. Research and Development Costs Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and benefits of research and development personnel, costs related to research activities, preclinical studies, clinical trials, drug manufacturing and allocated overhead and facility-related expenses. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations (“CROs”) and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses information it receives from internal personnel and outside service providers to estimate the clinical trial costs incurred. Stock-Based Compensation The Company determines employee, nonemployee and director stock-based compensation expense for all stock-based awards based on their grant date fair value using the Black-Scholes option-pricing model. For stock-based awards with service conditions only, stock-based compensation expense is recognized over the requisite service period using the straight-line method. Forfeitures are recognized as they occur. The fair value of restricted stock awards granted is determined based on the stock price on the date of grant. The estimated fair value is amortized as compensation expense over the service period of the award. Foreign Currency Transactions The functional currency of RAPT Therapeutics Australia Pty Ltd., the Company’s wholly-owned subsidiary, was the Australian dollar. Accordingly, all monetary assets and liabilities of the subsidiary were translated into U.S. dollars at the current period-end exchange rates and non-monetary assets were translated using historical exchange rates. Income and expense elements were remeasured to U.S. dollars using the average exchange rates in effect during the period. Remeasurement gains and losses are recorded as other income (expense), net. The Company is subject to foreign currency risk with respect to its clinical contracts denominated in currencies other than the U.S. dollar. Payments on contracts denominated in foreign currencies are made at the spot rate on the day of payment. The cumulative adjustment resulting from the translation of financial statements to the reporting currency is recorded in other comprehensive income (loss). Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period such tax rate changes are enacted. The Company recognizes the effect of income tax positions only if those positions are more likely than not to be sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely to be realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Valuation allowances are established when necessary to reduce deferred tax assets to amounts more likely than not to be realized. Interest and penalties related to unrecognized tax benefits are recognized as a component of income tax expense. Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ deficit that are excluded from net loss, primarily unrealized gains and losses from marketable securities and foreign currency translation adjustments. Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per common share is computed by dividing the net loss by the sum of the weighted average number of common shares outstanding during the period plus the number of potential dilutive securities outstanding during the period calculated in accordance with the treasury stock method. Diluted net loss per share is the same as basic net loss per share since the effect of potentially dilutive securities is anti-dilutive. Recent Accounting Pronouncements In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which provides updates to qualitative and quantitative reportable segment disclosure requirements, including enhanced disclosures about significant segment expenses and increased interim disclosure requirements, among others. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and interim periods in fiscal years beginning after December 15, 2024. Early adoption is permitted, and the amendments should be applied retrospectively. The Company believes the adoption of this standard will not have a material impact on its consolidated financial statement disclosures. In December 2023, the FASB issued ASU No. 2023-09, Improvements to Income Tax Disclosures, which requires disclosure of disaggregated income taxes paid, prescribes standard categories for the components of the effective tax rate reconciliation, and modifies other income tax-related disclosures. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024 and allows for adoption on a prospective basis, with a retrospective option. Early adoption is permitted. The Company is currently evaluating the impact of this standard on the income tax disclosures within the consolidated financial statements.

Net Loss Per Share - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net loss	$ (116,798)	$ (83,838)
Denominator:
Weighted-average shares used to compute net loss per share, basic	38,338,161	32,540,406
Weighted-average shares used to compute net loss per share, diluted	38,338,161	32,540,406
Net loss per share, basic	$ (3.05)	$ (2.58)
Net loss per share, diluted	$ (3.05)	$ (2.58)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued research and development expenses	$ 7,281	$ 3,473
Accrued compensation	6,303	4,618
Accrued professional and consulting services	341	327
Other	178	238
Total accrued expenses	$ 14,103	$ 8,656

Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

Fair value accounting is applied for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis (at least annually). Financial instruments include cash and cash equivalents, marketable securities, accounts payable and accrued expenses that approximate fair value due to their relatively short maturities.

Assets and liabilities recorded at fair value on a recurring basis in the balance sheet are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

Level 2—Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3—Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

The Company estimates the fair values of investments in corporate debt securities, commercial paper and U.S. government agency securities using valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data and other observable inputs.

Cash equivalents and marketable securities, all of which are classified as available-for-sale securities and measured at fair value on a recurring basis, consisted of the following (in thousands):


		As of December 31, 2023
	Fair Value Hierarchy Level	Amortized Cost			Unrealized Gains		Unrealized Losses			Fair Value
Financial assets:
Money market funds	Level 1	$	10,869		$	—	$	—		$	10,869
Corporate debt	Level 2		19,531			37		(9	)		19,559
Asset-backed securities	Level 2		5,242			7		(4	)		5,245
Commercial paper	Level 2		59,828			7		(8	)		59,827
U.S. government agency securities	Level 2		63,206			91		(18	)		63,279
Subtotal			158,676			142		(39	)		158,779
Less: Cash equivalents			(47,395	)		—		—			(47,395	)
Marketable securities		$	111,281		$	142	$	(39	)	$	111,384


		As of December 31, 2022
	Fair Value Hierarchy Level	Amortized Cost			Unrealized Gains		Unrealized Losses			Fair Value

Financial assets:
Money market funds	Level 1	$	38,658		$	—	$	—		$	38,658
Corporate debt	Level 2		71,149			30		(284	)		70,895
Asset-backed securities	Level 2		105			—		(1	)		104
Commercial paper	Level 2		71,328			—		—			71,328
U.S. government agency securities	Level 2		68,221			15		(441	)		67,795
Subtotal			249,461			45		(726	)		248,780
Less: Cash equivalents			(38,658	)		—		—			(38,658	)
Marketable securities		$	210,803		$	45	$	(726	)	$	210,122

As of December 31, 2023, the unrealized losses on the Company’s securities that were in an unrealized loss position were caused by interest rate changes and were not attributable to credit losses. The Company does not intend to sell the securities that are in an unrealized loss position and the Company believes it is more likely than not that the investments will be held until recovery of the amortized cost bases. The Company did not record an allowance for credit losses or other impairment charges related to its marketable securities as of December 31, 2023 and 2022.

The following table presents the remaining contractual maturities of the Company’s marketable securities as of December 31, 2023 (in thousands):


	December 31, 2023

Maturing in one year or less	$	97,039
Maturing after one year through five years		14,345
Total	$	111,384

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accrued Expenses

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	As of December 31,
	2023		2022
Accrued research and development expenses	$	7,281	$	3,473
Accrued compensation		6,303		4,618
Accrued professional and consulting services		341		327
Other		178		238
Total accrued expenses	$	14,103	$	8,656

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Loss per Share

The following table sets forth the computation of the basic and diluted net loss per share of the years ended December 31, 2023 and 2022 (in thousands, except share and per share data):


	Year Ended December 31,
	2023			2022
Numerator:
Net loss	$	(116,798	)	$	(83,838	)
Denominator:
Weighted-average shares used to compute net loss per share, basic and diluted		38,338,161			32,540,406
Net loss per share, basic and diluted	$	(3.05	)	$	(2.58	)

Potentially Dilutive Securities not Included in Diluted per Share Calculations

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:


	As of December 31,
	2023		2022
Stock options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan		4,099,947		2,993,280
Estimated shares issuable under the 2019 ESPP		21,904		14,276
RSUs subject to future vesting		13,500		27,000
Total		4,135,351		3,034,556

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Depreciation and amortization expenses	$ 1,216	$ 1,047

Stock-Based Compensation - Summary of RSU Activity (Details) - 2019 Plan - Restricted Stock Unit ("RSU")	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Outstanding, Beginning Balance \| shares	27,000
Number of Shares Outstanding, RSUs vested and settled \| shares	(13,500)
Number of Shares Outstanding, Ending Balance \| shares	13,500
Weighted Average Grant Date Fair Value Per Share, Beginning Balance \| $ / shares	$ 44.66
Weighted Average Grant Date Fair Value Per Share, RSUs vested and settled \| $ / shares	44.66
Weighted Average Grant Date Fair Value Per Share, Ending Balance \| $ / shares	$ 44.66

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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-Paragraph 2
-Subparagraph (f)(2)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(v)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Net Loss Per Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Net Loss Per Share

11. Net Loss Per Share

The following table sets forth the computation of the basic and diluted net loss per share of the years ended December 31, 2023 and 2022 (in thousands, except share and per share data):


	Year Ended December 31,
	2023			2022
Numerator:
Net loss	$	(116,798	)	$	(83,838	)
Denominator:
Weighted-average shares used to compute net loss per share, basic and diluted		38,338,161			32,540,406
Net loss per share, basic and diluted	$	(3.05	)	$	(2.58	)

For the years ended December 31, 2023 and 2022, 4,000,000 pre-funded warrants to purchase the Company's shares of common stock, issued in the May 2022 private placement financing (see Note 8), were included in the basic and diluted net loss per share calculation.

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:


	As of December 31,
	2023		2022
Stock options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan		4,099,947		2,993,280
Estimated shares issuable under the 2019 ESPP		21,904		14,276
RSUs subject to future vesting		13,500		27,000
Total		4,135,351		3,034,556

Stock-Based Compensation - Summary of Option Plans (Details) - Option Plans - Share-based Payment Arrangement, Option - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Outstanding, Beginning Balance	2,993,280
Number of Shares Outstanding, Stock options granted	1,218,608
Number of Shares Outstanding, Stock options exercised	(51,027)
Number of Shares Outstanding, Stock options cancelled	(60,914)
Number of Shares Outstanding, Ending Balance	4,099,947	2,993,280
Number of Shares Outstanding, Vested and expected to vest	4,099,947
Number of Shares Outstanding, Exercisable	2,366,831
Weighted Average Exercise Price Per Share, Beginning Balance	$ 18.95
Weighted Average Exercise Price Per Share, Stock options granted	25.61
Weighted Average Exercise Price Per Share, Stock options exercised	9.45
Weighted Average Exercise Price Per Share, Stock options cancelled	22.23
Weighted Average Exercise Price Per Share, Ending Balance	21.00	$ 18.95
Weighted Average Exercise Price Per Share, Vested and expected to vest	21.00
Weighted Average Exercise Price Per Share, Exercisable	$ 19.27
Average Remaining Contractual Term (Years), Balance	7 years 7 months 6 days	7 years 10 months 24 days
Average Remaining Contractual Term (Years), Vested and expected to vest	7 years 7 months 6 days
Average Remaining Contractual Term (Years), Exercisable	6 years 9 months 18 days
Aggregate Intrinsic Value	$ 23,206	$ 9,425
Aggregate Intrinsic Value, Vested and expected to vest	23,206
Aggregate Intrinsic Value, Exercisable	$ 17,598

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 47,478	$ 38,946
Marketable securities	111,384	210,122
Prepaid expenses and other current assets	2,920	3,626
Total current assets	161,782	252,694
Property and equipment, net	2,448	2,539
Operating lease right-of-use assets	5,228	6,940
Other assets	3,871	4,036
Total assets	173,329	266,209
Current liabilities:
Accounts payable	5,176	3,365
Accrued expenses	14,103	8,656
Operating lease liabilities, current	2,448	2,171
Other current liabilities	109	32
Total current liabilities	21,836	14,224
Operating lease liabilities, non-current	4,458	6,819
Total liabilities	26,294	21,043
Commitments (see note 6)
Stockholders' equity:
Preferred stock, $0.0001 par value: 50,000,000 shares authorized; no shares issued and outstanding at December 31, 2023 and 2022
Common stock, $0.0001 par value; 500,000,000 shares authorized; 34,398,312 and 34,254,314 shares issued and outstanding at December 31, 2023 and 2022, respectively	3	3
Additional paid-in capital	631,611	613,073
Accumulated other comprehensive gain (loss)	103	(26)
Accumulated deficit	(484,682)	(367,884)
Total stockholders' equity	147,035	245,166
Total liabilities and stockholders' equity	$ 173,329	$ 266,209

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and include the consolidated accounts of the Company and its wholly-owned subsidiary, RAPT Therapeutics Australia Pty Ltd., which was established in 2018 and deregistered during the quarter ended June 30, 2023. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its critical accounting policies or estimates related to revenue recognition, clinical trial accruals, fair value of assets and liabilities and stock-based compensation. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s balance sheets and the amounts of expenses and revenue reported for each of the periods presented are affected by estimates and assumptions. Actual results could differ from such estimates or assumptions.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products and protection of proprietary technology. If the Company does not successfully obtain regulatory approval, commercialize or partner any of its product candidates, it will be unable to generate revenue from product sales or achieve profitability. Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents and marketable securities. Substantially all the Company’s cash is held by two financial institutions. Such deposits may, at times, exceed federally insured limits. The Company invests its cash equivalents in highly rated money market funds and short-term marketable securities comprising commercial paper, corporate bonds and U.S. government agency securities.
Segments	Segments The Company operates as a single operating segment. The Company’s chief operating decision maker, its President and Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources, making operating decisions and evaluating financial performance.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amount of the Company’s financial instruments, including certain prepaid and accrued expenses, approximates fair value due to their short-term maturities.
Cash Equivalents	Cash Equivalents The Company considers all highly liquid investments with original maturities of 90 days or less from the date of purchase to be cash equivalents.
Marketable Securities	Marketable Securities Marketable securities primarily consist of commercial paper, corporate debt securities and U.S. government agency securities. The Company has classified its marketable securities as available-for-sale and may sell these securities prior to their stated maturities. The Company views these marketable securities as available to support current operations and classifies marketable securities with maturities beyond 12 months as current assets. The Company’s marketable securities are carried at estimated fair value, which is derived from independent pricing sources based on quoted prices in active markets for similar securities. Unrealized gains and losses are reported as a component of accumulated other comprehensive income (loss). The cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in other income, net on the consolidated statements of operations. All of the Company's available-for-sale investments are subject to a periodic impairment review. For each available-for-sale investment whose fair value is below its amortized cost, the Company determines if the impairment is a result of a credit-related loss or other factors using both quantitative and qualitative factors, including the length of time and extent to which the market value has been less than amortized cost, the financial condition and near-term prospects of the issuer and the Company’s intent and ability to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in market value. If the impairment is a result of a credit-related loss, the Company recognizes an allowance for credit losses. If the impairment is not a result of a credit loss, the Company recognizes the loss in other comprehensive loss.
Property and Equipment	Property and Equipment Property and equipment consist of computer equipment, laboratory equipment, leasehold improvements and furniture and fixtures, and is recorded at cost, less accumulated depreciation and amortization. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the improvements. Depreciation and amortization begin at the time the asset is placed in service. Maintenance and repairs are charged to expense as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in the results of operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets for impairment annually or more frequently whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparing the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. For the years ended December 31, 2023 and 2022, the Company did not record any impairment losses on long-lived assets.
Leases	Leases The Company adopted ASU No. 2016-02, Leases (Topic 842) on January 1, 2022 using the modified retrospective approach. The Company elected to apply the modified retrospective approach that allowed it to continue applying the guidance in effect, at the time of adoption, in the comparative periods presented in the Consolidated Balance Sheets and recognize a cumulative-effect adjustment to the opening balance of accumulated deficit on the date of adoption. The Company elected the package of practical expedients, which permits it not to reassess under the new standard the prior conclusions about lease identification, lease classification and initial direct costs. The Company also elected to combine lease components (for example, fixed rent payments) with non-lease components (for example, common-area maintenance costs) on the facilities asset class. Lastly, the Company elected the short-term lease practical expedients allowed under the standard and the practical expedient to use hindsight in determining the lease term for all its operating leases. At inception of a contract, the Company determines whether an arrangement is or contains a lease. For all leases, the Company determines the classification as either operating leases or financing leases. Operating leases are included in operating lease right-of-use (“ROU”) assets and operating lease liabilities in the Company’s consolidated balance sheets. Lease recognition occurs at the commencement date and lease liability amounts are based on the present value of lease payments over the lease term. The lease term may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. The Company uses an implicit rate when readily available, or its incremental borrowing rate based on the information available at lease commencement date, in determining the present value of lease payments. ROU assets represent the Company's right to use underlying assets for the lease term and operating lease liabilities represent the Company's obligation to make lease payments under the lease. ROU assets also include any lease payments made prior to the commencement date and exclude lease incentives received. Operating lease expense is recognized on a straight-line basis over the lease term. Lease agreements with both lease and nonlease components are generally accounted for together as a single lease component.
Revenue	Revenue License and collaborative agreements revenue consists of license, milestone and royalty payments generated through agreements with strategic partners for the development and commercialization of certain product candidates. The terms of an agreement may include a non-refundable upfront fee, payments based upon achievement of milestones and royalties on net product sales. If a portion of the nonrefundable upfront fee or other payments received is allocated to continuing performance obligations under the terms of an agreement, such portion is recorded as deferred revenue and recognized as revenue when or as the underlying performance obligation is satisfied. The Company recognizes revenue when it transfers promised goods or services to customers or counterparties in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized, the Company performs the following steps: (i) identification of the promised goods or services in the agreement; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the agreement; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to performance obligations based on estimated selling prices; and (v) recognition of revenue when or as the Company satisfies each performance obligation. Licenses: If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in an agreement, the Company will recognize revenue from the nonrefundable, upfront fee allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. If a license is bundled with other performance obligations, the Company utilizes judgment to assess the nature of the combined performance obligations to determine whether the combined performance obligations are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: If an agreement includes event-based or milestone payments, the Company evaluates whether the events or milestones are considered likely to be achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is unlikely that a significant revenue reversal of cumulative revenue recognized would occur, the value of the associated event-based or milestone payments is included in the transaction price. Event-based or milestone payments that are not within the control of the Company are not included in the transaction price until they become likely to be achieved. Royalties: If an agreement includes sales-based royalties and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and benefits of research and development personnel, costs related to research activities, preclinical studies, clinical trials, drug manufacturing and allocated overhead and facility-related expenses. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations (“CROs”) and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses information it receives from internal personnel and outside service providers to estimate the clinical trial costs incurred.
Share-Based Compensation	Stock-Based Compensation The Company determines employee, nonemployee and director stock-based compensation expense for all stock-based awards based on their grant date fair value using the Black-Scholes option-pricing model. For stock-based awards with service conditions only, stock-based compensation expense is recognized over the requisite service period using the straight-line method. Forfeitures are recognized as they occur. The fair value of restricted stock awards granted is determined based on the stock price on the date of grant. The estimated fair value is amortized as compensation expense over the service period of the award.
Foreign Currency Transactions	Foreign Currency Transactions The functional currency of RAPT Therapeutics Australia Pty Ltd., the Company’s wholly-owned subsidiary, was the Australian dollar. Accordingly, all monetary assets and liabilities of the subsidiary were translated into U.S. dollars at the current period-end exchange rates and non-monetary assets were translated using historical exchange rates. Income and expense elements were remeasured to U.S. dollars using the average exchange rates in effect during the period. Remeasurement gains and losses are recorded as other income (expense), net. The Company is subject to foreign currency risk with respect to its clinical contracts denominated in currencies other than the U.S. dollar. Payments on contracts denominated in foreign currencies are made at the spot rate on the day of payment. The cumulative adjustment resulting from the translation of financial statements to the reporting currency is recorded in other comprehensive income (loss).
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period such tax rate changes are enacted. The Company recognizes the effect of income tax positions only if those positions are more likely than not to be sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely to be realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Valuation allowances are established when necessary to reduce deferred tax assets to amounts more likely than not to be realized. Interest and penalties related to unrecognized tax benefits are recognized as a component of income tax expense.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ deficit that are excluded from net loss, primarily unrealized gains and losses from marketable securities and foreign currency translation adjustments.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per common share is computed by dividing the net loss by the sum of the weighted average number of common shares outstanding during the period plus the number of potential dilutive securities outstanding during the period calculated in accordance with the treasury stock method. Diluted net loss per share is the same as basic net loss per share since the effect of potentially dilutive securities is anti-dilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which provides updates to qualitative and quantitative reportable segment disclosure requirements, including enhanced disclosures about significant segment expenses and increased interim disclosure requirements, among others. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and interim periods in fiscal years beginning after December 15, 2024. Early adoption is permitted, and the amendments should be applied retrospectively. The Company believes the adoption of this standard will not have a material impact on its consolidated financial statement disclosures. In December 2023, the FASB issued ASU No. 2023-09, Improvements to Income Tax Disclosures, which requires disclosure of disaggregated income taxes paid, prescribes standard categories for the components of the effective tax rate reconciliation, and modifies other income tax-related disclosures. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024 and allows for adoption on a prospective basis, with a retrospective option. Early adoption is permitted. The Company is currently evaluating the impact of this standard on the income tax disclosures within the consolidated financial statements.

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of Domestic and Foreign Components of Income (Loss) before Income Taxes

The following table presents domestic and foreign components of income (loss) before income taxes for the periods presented (in thousands):


	December 31,
	2023			2022
United States	$	(116,798	)	$	(89,223	)
Foreign		—			5,385
	$	(116,798	)	$	(83,838	)

Schedule of Effective Income Tax Rate Reconciliation

A reconciliation of the statutory U.S. federal rate and effective rate is as follows:


	December 31,
	2023			2022
Federal tax		21.0	%		21.0	%
Stock-based compensation		(0.9	)		(0.7	)
Research and development tax credit		2.4			2.5
Foreign losses not benefited		—			1.8
Global Intangible Low-taxed Income (GILTI)		—			(1.4	)
Change in valuation allowance		(22.4	)		(24.5	)
Other		(0.1	)		1.3
Income tax expense		—	%		—	%

Schedule of Components of Deferred Tax Assets and Liabilities

The components of the Company’s deferred tax assets and liabilities are as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carryforwards	$	58,248		$	52,818
Federal and state research and development tax credits		12,601			9,834
Accrued liabilities and reserves		1,234			983
Stock-based compensation		6,238			3,871
Depreciation and amortization		689			672
Lease liability		1,450			1,888
Research and development capitalized expenditures		27,290			11,834
Gross deferred tax assets		107,750			81,900
Valuation allowance		(106,652	)		(80,443	)
Deferred tax liabilities:
Right of use asset		(1,098	)		(1,457	)
Gross deferred tax liabilities		(1,098	)		(1,457	)
Net deferred taxes	$	—		$	—

Schedule of Reconciliation of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amounts of unrecognized tax benefits for the years ended December 31, 2023 and 2022 resulting primarily from research and development tax credits claimed for both U.S. and foreign operations on the Company’s annual tax returns were as follows (in thousands):


	December 31,
	2023			2022
Balance at beginning of year	$	3,663		$	4,434
Additions on tax positions related to prior years		(3	)		(1,530	)
Additions on tax positions related to current year		1,014			759
Balance at end of year	$	4,674		$	3,663

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating activities
Net loss	$ (116,798)	$ (83,838)
Adjustments to reconcile net loss to net cash used in operating activities:
Accretion of discounts on marketable securities	(5,736)	(296)
Depreciation and amortization	1,216	1,047
Stock-based compensation expense	17,091	11,264
Gain (loss) on foreign currency translation	(655)	627
Non- cash operating lease expense	2,335	1,760
Changes in operating assets and liabilities:
Prepaid expenses and other assets	871	(1,421)
Accounts payable, accrued expenses, and other current liabilities	7,335	3,710
Deferred revenue	0	(1,527)
Operating lease liabilities	(2,707)	(2,097)
Net cash used in operating activities	(97,048)	(70,771)
Investing activities
Purchase of marketable securities	(161,497)	(190,856)
Proceeds from maturities of marketable securities	266,755	146,211
Purchase of property and equipment	(1,125)	(845)
Net cash provided by (used in) investing activities	104,133	(45,490)
Financing activities
Proceeds from issuance of common stock under employee stock plans	1,447	1,392
Net cash provided by financing activities	1,447	131,180
Net increase in cash and cash equivalents	8,532	14,919
Cash and cash equivalents at beginning of period	38,946	24,027
Cash and cash equivalents at end of period	47,478	38,946
Supplemental disclosures of non-cash investing information
Right-of-use asset obtained in exchange for lease obligation	0	8,063
Public Offering
Financing activities
Proceeds from equity offerings, net of issuance costs	0	124,810
At The Market
Financing activities
Proceeds from equity offerings, net of issuance costs	$ 0	$ 4,978

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
Revenue	$ 0	$ 1,527
Operating expenses:
Research and development	101,002	67,082
General and administrative	26,060	20,240
Total operating expenses	127,062	87,322
Loss from operations	(127,062)	(85,795)
Other income, net	10,264	1,957
Net loss	(116,798)	(83,838)
Other comprehensive income (loss):
Foreign currency translation gain (loss)	(655)	627
Unrealized gain (loss) on marketable securities	784	(447)
Total comprehensive loss	$ (116,669)	$ (83,658)
Net loss per share, basic	$ (3.05)	$ (2.58)
Net loss per share, diluted	$ (3.05)	$ (2.58)
Weighted average number of shares used in computing net loss per share, basic	38,338,161	32,540,406
Weighted average number of shares used in computing net loss per share, diluted	38,338,161	32,540,406

Commitments - Additional Information (Details)	1 Months Ended			12 Months Ended
Commitments - Additional Information (Details)	Nov. 30, 2022 ft²	Apr. 30, 2018 ft²	May 31, 2015 ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Lessee Lease Description [Line Items]
Contingency losses, accrued \| $				$ 0	$ 0
Lease expiration period	2025-07
Additional laboratory and office facilities under lease \| ft²		6,378
Increased of leased premises \| ft²		36,754
Lessee operating lease extended lease term		2026-11
Lease existence of option to extend	true		true
Lessee operating lease option to extend	6 months		5 years
Lease expense \| $				2,300,000	1,700,000
Rent expense \| $				2,900,000	$ 2,200,000
Cash paid for operating lease liabilities \| $				$ 2,700,000
Operating lease, weighted average remaining lease term				2 years 7 months 24 days
Operating lease, weighted average discount rate, percent					8.21%
South San Francisco and California
Lessee Lease Description [Line Items]
Laboratory and office facilities under lease \| ft²			30,376
Additional office facilities under lease \| ft²	13,232

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	As of December 31,
	2023		2022
Accrued research and development expenses	$	7,281	$	3,473
Accrued compensation		6,303		4,618
Accrued professional and consulting services		341		327
Other		178		238
Total accrued expenses	$	14,103	$	8,656

Property and Equipment

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment

4. Property and Equipment

Property and equipment consisted of the following (in thousands):


	As of December 31,
	2023			2022
Laboratory equipment	$	7,399		$	6,558
Leasehold improvements		3,295			3,295
Computer equipment		727			578
Furniture and fixtures		394			357
Total property and equipment		11,815			10,788
Less accumulated depreciation and amortization		(9,367	)		(8,249	)
Property and equipment, net	$	2,448		$	2,539

Depreciation and amortization expenses were $1.2 million and $1.0 million for the years ended December 31, 2023 and 2022, respectively.

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Schedule of Cash Equivalents and Marketable Securities Classified as Available-for-Sale Securities Measured at Fair Value on Recurring Basis

Cash equivalents and marketable securities, all of which are classified as available-for-sale securities and measured at fair value on a recurring basis, consisted of the following (in thousands):


		As of December 31, 2023
	Fair Value Hierarchy Level	Amortized Cost			Unrealized Gains		Unrealized Losses			Fair Value
Financial assets:
Money market funds	Level 1	$	10,869		$	—	$	—		$	10,869
Corporate debt	Level 2		19,531			37		(9	)		19,559
Asset-backed securities	Level 2		5,242			7		(4	)		5,245
Commercial paper	Level 2		59,828			7		(8	)		59,827
U.S. government agency securities	Level 2		63,206			91		(18	)		63,279
Subtotal			158,676			142		(39	)		158,779
Less: Cash equivalents			(47,395	)		—		—			(47,395	)
Marketable securities		$	111,281		$	142	$	(39	)	$	111,384


		As of December 31, 2022
	Fair Value Hierarchy Level	Amortized Cost			Unrealized Gains		Unrealized Losses			Fair Value

Financial assets:
Money market funds	Level 1	$	38,658		$	—	$	—		$	38,658
Corporate debt	Level 2		71,149			30		(284	)		70,895
Asset-backed securities	Level 2		105			—		(1	)		104
Commercial paper	Level 2		71,328			—		—			71,328
U.S. government agency securities	Level 2		68,221			15		(441	)		67,795
Subtotal			249,461			45		(726	)		248,780
Less: Cash equivalents			(38,658	)		—		—			(38,658	)
Marketable securities		$	210,803		$	45	$	(726	)	$	210,122

Schedule of Remaining Contractual Maturities of Marketable Securities

The following table presents the remaining contractual maturities of the Company’s marketable securities as of December 31, 2023 (in thousands):


	December 31, 2023

Maturing in one year or less	$	97,039
Maturing after one year through five years		14,345
Total	$	111,384

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 9
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

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Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
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-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Summary of Option Plans

Stock Options

Stock option activity under the 2019 Plan is set forth below for the year ended December 31, 2023:


				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Shares			Price Per		Term		Value
	Outstanding			Share		(Years)		(in thousands)
Balances at December 31, 2022		2,993,280		$	18.95		7.9	$	9,425
Stock options granted		1,218,608			25.61
Stock options exercised		(51,027	)		9.45
Stock options cancelled		(60,914	)		22.23
Balances at December 31, 2023		4,099,947		$	21.00		7.6	$	23,206
Vested and expected to vest at December 31, 2023		4,099,947			21.00		7.6	$	23,206
Exercisable at December 31, 2023		2,366,831			19.27	6.8		$	17,598

Summary of RSU Activity

Restricted Stock Units (“RSU”) activity under the 2019 Plan is set forth below for the year ended December 31, 2023:


				Weighted
				Average
	Number of			Grant Date
	Shares			Fair Value
	Outstanding			Per Share
Balances at December 31, 2022		27,000		$	44.66
RSUs granted		—			—
RSUs vested and settled		(13,500	)		44.66
RSUs forfeited		—			—
Balances at December 31, 2023		13,500		$	44.66

Summary of Assumptions Used to Value Under Stock Option Plans

The fair value of the rights granted to employees under the 2019 ESPP was estimated using a Black-Scholes option-pricing model with the following valuation assumptions:


	For the Year Ended December 31,
	2023	2022
Fair value	$4.79 - $12.12	$6.53 - $14.89
Expected term (in years)	0.50 - 2.00	0.50 - 2.00
Volatility	64.3% - 93.2%	91.0% - 101.5%
Risk-free interest rate	4.14% - 5.51%	1.49% - 4.75%
Dividend yield	—	—

Summary of Stock-based Compensation Expense

Total stock-based compensation expense recognized for stock options and RSUs granted to both employees and non-employees and for the employee stock purchase plan was as follows (in thousands):


	For the Year Ended December 31,
	2023		2022
Research and development	$	7,941	$	5,206
General and administrative		9,150		6,058
Total stock-based compensation expense	$	17,091	$	11,264

Employee and Non-employees

Summary of Assumptions Used to Value Under Stock Option Plans


	For the Year Ended December 31,
	2023	2022
Fair value	$11.25 - $23.70	$10.35 - $28.63
Expected term (in years)	5.87 - 6.06	5.79 - 6.08
Volatility	94.9% - 97.8%	89.8% - 94.3%
Risk-free interest rate	3.46% - 4.71%	1.42% - 4.09%
Dividend yield	—	—

Income Taxes - Schedule of Domestic and Foreign Components of Income (Loss) before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
United States	$ (116,798)	$ (89,223)
Foreign		5,385
Net loss before taxes	$ (116,798)	$ (83,838)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(11))
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+ Details

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

The following table presents domestic and foreign components of income (loss) before income taxes for the periods presented (in thousands):


	December 31,
	2023			2022
United States	$	(116,798	)	$	(89,223	)
Foreign		—			5,385
	$	(116,798	)	$	(83,838	)

A reconciliation of the statutory U.S. federal rate and effective rate is as follows:


	December 31,
	2023			2022
Federal tax		21.0	%		21.0	%
Stock-based compensation		(0.9	)		(0.7	)
Research and development tax credit		2.4			2.5
Foreign losses not benefited		—			1.8
Global Intangible Low-taxed Income (GILTI)		—			(1.4	)
Change in valuation allowance		(22.4	)		(24.5	)
Other		(0.1	)		1.3
Income tax expense		—	%		—	%

The Company has incurred net operating losses for all periods since inception. The Company has not reflected any benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets.

The components of the Company’s deferred tax assets and liabilities are as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carryforwards	$	58,248		$	52,818
Federal and state research and development tax credits		12,601			9,834
Accrued liabilities and reserves		1,234			983
Stock-based compensation		6,238			3,871
Depreciation and amortization		689			672
Lease liability		1,450			1,888
Research and development capitalized expenditures		27,290			11,834
Gross deferred tax assets		107,750			81,900
Valuation allowance		(106,652	)		(80,443	)
Deferred tax liabilities:
Right of use asset		(1,098	)		(1,457	)
Gross deferred tax liabilities		(1,098	)		(1,457	)
Net deferred taxes	$	—		$	—

In accordance with the 2017 Tax Act, research and experimentation (R&E) expenses under Internal Revenue Code Section 174 are required to be capitalized beginning in 2022. R&E expenses are required to be amortized over a period of 5 years for domestic expenses and 15 years for foreign expenses. As a result of this provision of the 2017 Tax Act, deferred tax assets related to capitalized research expenses increased by $15.5 million and $11.8 million during the years ended December 31, 2023 and 2022, respectively.

Realization of deferred tax assets is dependent upon future taxable income, if any. The Company has established a valuation allowance to offset deferred tax assets as of December 31, 2023 and 2022, due to the uncertainty of realizing future tax benefits from its net operating loss carryforwards and other deferred tax assets. The valuation allowance increased by approximately $26.2 million and $19.0 million during the years ended December 31, 2023 and 2022, respectively. The increase in the valuation allowance is mainly related to the capitalization of research and development expenses under Internal Revenue Code Section 174 and an increase in net operating loss carryforwards incurred during the respective taxable years.

As of December 31, 2023 and 2022, the Company had federal net operating loss carryforwards of approximately $273.3 million and $247.5 million, respectively. The federal net operating loss carryforwards generated during and after fiscal 2018 are carried forward indefinitely, while all others, along with the federal tax credit carryforwards, expire in years beginning in 2035. As of December 31, 2023 and 2022, the Company had state net operating loss carryforwards of approximately $12.1 million, which begin to expire in 2035 and are available to offset future taxable income. As of December 31, 2023 and 2022, the Company had federal research and development tax credit carryforwards of approximately $10.2 million and $7.8 million, respectively. As of December 31, 2023 and 2022, the Company had state research and development tax credit carryforwards of approximately $8.4 million and $6.7 million, respectively. Moreover, as of December 31, 2023, the Company recorded federal and state reserves of approximately $2.6 million and $2.1 million, respectively, as uncertain tax positions. If not utilized, the federal credit carryforwards will begin expiring in 2035. The state credits carry forward indefinitely.

Federal and state laws impose substantial restrictions on the utilization of net operating loss and tax credit carryforwards in the event of an ownership change for tax purposes, as defined in Section 382 of the Internal Revenue Code. As a result of such ownership changes, the Company’s ability to realize the potential future benefit of tax losses and tax credits that existed at the time of the ownership change may be significantly reduced. The Company’s deferred tax asset and related valuation allowance would be reduced as a result. The Company has not yet performed a Section 382 study to determine the amount of reduction, if any. The annual limitation may result in the expiration of net operating losses and credits before utilization. Under the new enacted law, the carryforward period of net operating losses generated from 2018 forward is indefinite; however, the carryforward period for net operating losses generated prior to 2018 remains the same. Therefore, the annual limitation may still result in the expiration of certain net operating losses and tax credit carryforwards before their utilization. On February 9, 2022, California Senate Bill 113 “SB 113” was signed into law. SB 113 lifted the limitation for California NOL and Credit utilization disallowed by California Assembly Bill 85. Given the Company’s loss position, the new legislations did not impact the Company's tax provision. The Company will continue to monitor possible California net operating loss and credit limitation in future periods.

Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50 percent likely of being realized upon effective settlement.


	December 31,
	2023			2022
Balance at beginning of year	$	3,663		$	4,434
Additions on tax positions related to prior years		(3	)		(1,530	)
Additions on tax positions related to current year		1,014			759
Balance at end of year	$	4,674		$	3,663

The Company does not expect that its uncertain tax positions will materially change in the next 12 months. The reversal of uncertain tax benefits would not impact the Company’s effective tax rate as the Company continues to maintain a full valuation allowance against its deferred tax assets. In accordance with ASC 740, the Company would classify interest and penalties related to uncertain tax positions in income tax expense, if applicable. There was no interest expense or penalties related to unrecognized tax benefits through December 31, 2023.

The Company files income tax returns with varying statutes of limitations in the United States and various states. The Company is not currently under examination by income tax authorities in federal, state or other jurisdictions. All tax returns remain open for examination by federal and state authorities. The tax years from inception in 2015 forward remain open to examination due to the carryover of unused net operating losses and tax credits.

The Inflation Reduction Act of 2022 was signed into law on August 16, 2022, and contained several tax provisions to curb inflation by reducing the deficit, lowering prescription drug prices, investing into domestic energy production while promoting clean energy, and introduced the topic of corporate alternative minimum tax on applicable corporations. There is no impact to the Company’s current tax provision from this new legislation.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (b)
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Commitments - Summary of Maturities of Lease Liabilities (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2024	$ 2,855
2025	2,662
2026	2,137
Total future undiscounted lease payments	7,654
Less: Imputed interest	(748)
Total lease liabilities	$ 6,906

Common Stock (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Summary of Reserved Shares of Common Stock on Converted Basis for Future Issuance

The Company had reserved the following shares of common stock, on an as-converted basis, for future issuance as follows:


	Year Ended December 31,
	2023		2022
Options issued and outstanding under the 2019 Equity Incentive Plan and 2015 Stock Plan		4,099,947		2,993,280
Restricted stock units issued and outstanding under the 2019 Equity Incentive Plan		13,500		27,000
Options available for future grants		3,032,820		2,820,341
Pre-funded warrants issued and outstanding		4,000,000		4,000,000
Shares reserved under the 2019 Employee Stock Purchase Plan		410,522		498,193
Total		11,556,789		10,338,814

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	34,398,312	34,254,314
Common stock, shares outstanding	34,398,312	34,254,314

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Mar. 04, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Trading Symbol	RAPT
Entity Registrant Name	RAPT THERAPEUTICS, INC.
Entity Central Index Key	0001673772
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Document Financial Statement Error Correction	false
Entity File Number	001-38997
Entity Tax Identification Number	47-3313701
Entity Address, Address Line One	561 Eccles Avenue
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	489-9000
Entity Common Stock, Shares Outstanding		34,797,702
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 399
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	San Mateo, California
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Registrant’s Definitive Proxy Statement for the 2024 Annual Meeting of Stockholders to be filed with the U.S. Securities and Exchange Commission pursuant to Regulation 14A within 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K are incorporated by reference in Part III, Items 10-14 of this Annual Report on Form 10-K.

Collaboration Agreements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Apr. 30, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized	$ 0	$ 1,527,000
Collaboration and License Agreement \| Hanmi Pharmaceutical Co., LTD
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront and near-term milestone payment	10,400,000			$ 10,000,000.0
Upfront fee	4,000,000.0			4,000,000.0
Development milestone payment			$ 6,000,000.0
Unconstrained development milestone payment	6,000,000.0
Increase in transaction price	400,000
Revenue recognized	0	$ 1,500,000
Deferred revenue	$ 0
Collaboration and License Agreement \| Hanmi Pharmaceutical Co., LTD \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments upon achievement of specified milestones				$ 108,000,000.0

Collaboration Agreements

12 Months Ended

Dec. 31, 2023

Collaboration Agreements [Abstract]

Collaboration Agreements

7. Collaboration Agreements

Collaboration and License Agreement with Hanmi

In December 2019, the Company entered into a Collaboration and License Agreement (the “Hanmi Agreement”), with Hanmi Pharmaceutical Ltd. ("Hanmi"), pursuant to which the Company granted Hanmi an exclusive license to develop, manufacture and commercialize tivumecirnon and related compounds and products with respect to human cancers in the Republic of Korea, the Republic of China (Taiwan) and the People’s Republic of China, including the special administrative regions of Macau and Hong Kong (the “Hanmi Territory”), and certain sublicense rights.

In consideration of such rights, under the Hanmi Agreement, the Company was entitled to $10.0 million, which consisted of an upfront payment of $4.0 million and a development milestone payment of $6.0 million that were received in December 2019 and April 2020, respectively. Additionally, the Company is eligible to receive contingent payments of up to $108.0 million upon the achievement of specified milestones, as well as double-digit royalties on future net sales of tivumecirnon in the Hanmi Territory.

The Company identified the following promised goods and services at the inception of the Hanmi Agreement, including (1) the exclusive development, manufacturing and commercialization license in the Hanmi Territory; (2) the transfer of know-how, technology, research data and information, and any improvements in technology; (3) the obligation to participate in the joint steering committee and appoint an alliance manager; (4) the responsibility to complete certain Phase 2 clinical trials; and (5) the supply of tivumecirnon for use in Hanmi’s Phase 2 clinical trials for which Hanmi will reimburse the Company for the supply of tivumecirnon.

The Company determined that the identified performance obligations, except for the supply of tivumecirnon, are not distinct and should be combined into one distinct performance obligation. The Company considered factors such as the novelty of the drug candidate and that the promised goods and services are highly interdependent and are expected to significantly modify one another.

The Company determined that the transaction price was $10.4 million, which consisted of the upfront fee of $4.0 million and an unconstrained development milestone payment of $6.0 million. In addition, Hanmi requested the Company to supply tivumecirnon, and as a result, the Company increased the transaction price by $0.4 million. Other future development milestones were constrained as their achievement was highly dependent on factors outside the Company’s control. The Company expects that the revenue from sales milestone and royalty payments will be recognized when the sales occur or the milestone is achieved. The Company will re-evaluate the transaction price at each reporting period.

The Company recognizes revenue for the performance obligation by applying the cost-based input method over the estimated service period. The Company determined that this method most faithfully depicts the transfer of its performance

obligations to Hanmi as it reflects the progress made towards providing Hanmi with the necessary know-how to continue developing tivumecirnon in the Hanmi Territory.

The Company did not recognize revenue for the year ended December 31, 2023, and recognized revenue of $1.5 million for the year ended December 31, 2022 , pursuant to the Hanmi Agreement. As of December 31, 2023, there was no remaining deferred revenue related to the Hanmi Agreement, as the performance obligation of providing Hanmi with the necessary know-how to develop tivumecirnon in the Hanmi Territory was substantially complete as of the second quarter of 2022.

Clinical Trial Collaboration and Supply Agreement with Merck

In November 2018, the Company entered into a clinical trial collaboration and supply agreement with an affiliate of Merck (known as MSD outside the United States and Canada) under which the Company will conduct a clinical trial evaluating tivumecirnon in combination with pembrolizumab (KEYTRUDA®), Merck’s anti-PD-1 therapy, in patients with advanced cancers. The Company is the sponsor of the clinical trial, and Merck will supply pembrolizumab for use in the clinical trial. In March 2022 and February 2024, the Company and Merck amended the agreement to provide for additional supply of pembrolizumab.

Net Loss Per Share - Potentially Dilutive Securities not Included in Diluted per Share Calculations (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	4,135,351	3,034,556
Stock Options Issued And Outstanding Equity Incentive Plan And Under 2019 Equity Incentive Plan And 2015 Stock Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	4,099,947	2,993,280
Estimated Shares Issuable Under Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	21,904	14,276
RSUs Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	13,500	27,000

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Institution	Dec. 31, 2022 USD ($)
Significant Accounting Policies [Line Items]
Number of financial institutions \| Institution	2
Impairment losses on long-lived assets \| $	$ 0	$ 0
Minimum [Member]
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	3 years
Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	5 years

Organization

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Organization

1. Organization

Description of the Business

RAPT Therapeutics, Inc. (“RAPT” or the “Company”) is a clinical-stage, immunology-based biopharmaceutical company focused on discovering, developing and commercializing oral small molecule therapies for patients with significant unmet needs in inflammatory diseases and oncology. Utilizing its proprietary drug discovery and development engine, the Company develops highly selective small molecules that are designed to modulate the critical immune responses underlying these diseases. The Company is located in South San Francisco, California.

Liquidity and Management Plans

The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern. Since inception, the Company has incurred net losses and negative cash flows from operations. During the year ended December 31, 2023, the Company incurred a net loss of $116.8 million and used $97.0 million of cash in operations. At December 31, 2023, the Company had cash and cash equivalents and marketable securities of $158.9 million and working capital of $139.9 million.

Management plans to continue to incur substantial costs in order to conduct research and development activities and additional capital will be needed to undertake these activities. The Company intends to raise such capital through the issuance of additional equity, borrowings and strategic alliances with other companies. However, if such arrangements are not available at adequate levels or on acceptable terms, the Company would be required to significantly reduce operating expenses and delay or reduce the scope of or eliminate some of its development programs. Management believes that the Company’s current cash and cash equivalents and marketable securities will provide sufficient funds to enable the Company to meet its obligations for at least 12 months from the filing date of this report.

Management’s evaluation was based on the facts known as of the date of filing of this Annual Report on Form 10-K, including the impacts of the clinical hold that FDA has placed on the Phase 2b trial of zelnecirnon in AD and the Phase 2a trial in asthma.

Commitments

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments

6. Commitments

The Company enters into contracts in the normal course of business with CROs for preclinical studies and clinical trials. These agreements provide for notice of termination by either party and are, therefore, cancelable contracts.

From time to time, the Company may be subject to various legal proceedings and claims arising in the ordinary course of business. The Company assesses contingencies to determine the degree of probability and range of possible loss for potential accrual in its financial statements. An estimated loss contingency is accrued in the financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. The Company is not subject to any current pending legal matters or claims and no contingency losses were accrued at either December 31, 2023 and 2022.

Leases

In May 2015, the Company entered into an operating lease for 30,376 square feet of laboratory and office facilities in South San Francisco, California. In April 2018, the Company amended the lease agreement to include an additional 6,378 square feet of laboratory and office space increasing the total leased premises to 36,754 square feet. The lease amendment extended the lease term to November 2026 and contained scheduled rent increases over the lease term and an option for the Company to extend the lease for an additional five-year term.

In November 2022, the Company entered into an operating lease for 13,232 square feet of office facilities in South San Francisco, California, which expires in July 2025. The lease agreement contained an option to extend the lease for an additional six-month term.

Cash paid for amounts included in the measurement of operating lease liabilities for the year ended December 31, 2023 was $2.7 million and was included in net cash used in operating activities in the Company’s consolidated statements of cash flows.

As of December 31, 2023, the weighted-average remaining lease term and discount rate for the Company’s operating leases was 2.65 years and 8.21%, respectively.

The following table summarizes maturities of operating lease liabilities as of December 31, 2023 (in thousands):


2024	$	2,855
2025		2,662
2026		2,137
Thereafter		—
Total future undiscounted lease payments		7,654
Less: Imputed interest		(748	)
Total lease liabilities	$	6,906

The following table summarizes the supplemental balance sheet information related to operating leases at December 31, 2023 (in thousands):


Operating leases
Operating lease right-of-use assets	$	5,228

Operating lease liabilities, current		2,448
Operating lease liabilities, non-current		4,458
Total operating lease liabilities	$	6,906

For the years ended December 31, 2023 and 2022, the Company incurred $2.3 million and $1.7 million, respectively, of lease expense included in operating expenses in the consolidated statement of operations in relation to the operating lease. Variable lease expense was insignificant for the years ended December 31, 2023 and 2022. Rent expense was $2.9 million and $2.2 million in the years ended December 31, 2023 and 2022, respectively. The Company does not have any financing lease agreements as of December 31, 2023.

Organization - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net loss	$ 116,798	$ 83,838
Cash used in operations	97,048	$ 70,771
Cash and cash equivalents and marketable securities	158,900
Working capital	$ 139,900

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal tax	21.00%	21.00%
Stock-based compensation	(0.90%)	(0.70%)
Research and development tax credit	2.40%	2.50%
Foreign losses not benefited		1.80%
Global Intangible Low-taxed Income (GILTI)		(1.40%)
Change in valuation allowance	(22.40%)	(24.50%)
Other	(0.10%)	1.30%

Fair Value Measurements - Schedule of Cash Equivalents and Marketable Securities Classified as Available-for-Sale Securities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 158,676	$ 249,461
Unrealized Gains	142	45
Unrealized Losses	(39)	(726)
Fair Value	158,779	248,780
Less: Cash equivalents	(47,395)	(38,658)
Marketable securities, Amortized Cost	111,281	210,803
Marketable securities, Unrealized Gains	142	45
Marketable securities, Unrealized Losses	(39)	(726)
Marketable securities, Fair Value	111,384	210,122
Level 1 \| Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	10,869	38,658
Fair Value	10,869	38,658
Level 2 \| Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,531	71,149
Unrealized Gains	37	30
Unrealized Losses	(9)	(284)
Fair Value	19,559	70,895
Level 2 \| Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,242	105
Unrealized Gains	7
Unrealized Losses	(4)	(1)
Fair Value	5,245	104
Level 2 \| Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	59,828	71,328
Unrealized Gains	7
Unrealized Losses	(8)
Fair Value	59,827	71,328
Level 2 \| U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	63,206	68,221
Unrealized Gains	91	15
Unrealized Losses	(18)	(441)
Fair Value	$ 63,279	$ 67,795

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following (in thousands):


	As of December 31,
	2023			2022
Laboratory equipment	$	7,399		$	6,558
Leasehold improvements		3,295			3,295
Computer equipment		727			578
Furniture and fixtures		394			357
Total property and equipment		11,815			10,788
Less accumulated depreciation and amortization		(9,367	)		(8,249	)
Property and equipment, net	$	2,448		$	2,539

Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 58,248	$ 52,818
Federal and state research and development tax credits	12,601	9,834
Accrued liabilities and reserves	1,234	983
Stock-based compensation	6,238	3,871
Depreciation and amortization	689	672
Lease liabilities	1,450	1,888
Research and development capitalized expenditures	27,290	11,834
Gross deferred tax assets	107,750	81,900
Valuation allowance	(106,652)	(80,443)
Deferred tax liabilities:
Right-of-use asset	(1,098)	(1,457)
Gross deferred tax liabilities	(1,098)	(1,457)
Net deferred taxes	$ 0	$ 0

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 3,663	$ 4,434
Additions on tax positions related to prior years	(3)	(1,530)
Additions on tax positions related to current year	1,014	759
Balance at end of year	$ 4,674	$ 3,663

Fair Value Measurements - Additional Information (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Allowance for credit losses or other impairment charges related to marketable securities	$ 0	$ 0

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2019	Dec. 31, 2023	Dec. 31, 2022	Jan. 01, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common stock reserved for issuance		11,556,789	10,338,814
Cash received from stock option exercises		$ 500	$ 700
Stock-based compensation expense		$ 17,091	$ 11,264
Weighted-average grant-date fair value per share		$ 20.20	$ 14.82
Stock options grant date fair value		$ 24,600	$ 16,800
Number of stock options, exercises intrinsic value		700	1,300
Stock option vested aggregate fair value		15,200	9,700
Expected dividend yield		0
Unrecognized stock-based compensation cost related to outstanding unvested stock options and RSUs that are expected to vest		$ 29,200
Unrecognized stock-based compensation cost, expected period to be recognized		2 years 7 months 6 days
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in shares reserved for issuance on common stock outstanding	1.00%
Total shares reserved	240,336			0
Increase in shares at the beginning of each calendar year	240,336
Maximum employee subscription rate on salary	15.00%
Offering period	24 months
Purchase period	6 months
Purchase price of common stock as percentage of fair market value	85.00%
Stock-based compensation expense		$ 1,300	$ 900
Share-based compensation, employee purchased shares		87,671	59,066
Share-based compensation, shares at weighted average exercise price		$ 12.34	$ 12.86
Option Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for grant		3,032,820
Option Plans \| Employees, Officers, Directors, Advisors, and Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period		4 years
Additional common stock reserved for issuance				1,370,173
Option Plans \| Maximum \| Employees, Officers, Directors, Advisors, and Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted, expiration period		10 years
2019 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in shares reserved for issuance on common stock outstanding		4.00%

Fair Value Measurements - Schedule of Remaining Contractual Maturities of Marketable Securities (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Investments, Debt and Equity Securities [Abstract]
Maturing in one year or less	$ 97,039
Maturing after one year through five years	14,345
Total	$ 111,384

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Line Items]
Increase in valuation allowance	$ 26,200,000	$ 19,000,000.0
Interest expense or penalties related to unrecognized tax benefits	0
Increase in deferred tax assets related to capitalized research expenses	15,500,000	11,800,000
Federal
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 273,300,000	247,500,000
Operating loss carryforwards expiration beginning year	2035
Uncertain tax positions reserves	$ 2,100,000
Research and experimental expenses required to amortized term	5 years
Federal \| Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards amount	$ 10,200,000	7,800,000
State
Income Tax Disclosure [Line Items]
Operating loss carryforwards	$ 12,100,000	12,100,000
Operating loss carryforwards expiration beginning year	2035
Uncertain tax positions reserves	$ 2,600,000
State \| Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards amount	$ 6,700,000	$ 6,700,000
Foreign
Income Tax Disclosure [Line Items]
Research and experimental expenses required to amortized term	15 years

Common Stock - Summary of Reserved Shares of Common Stock on Converted Basis for Future Issuance (Detail) - shares	Dec. 31, 2023	Dec. 31, 2022
Class Of Stock [Line Items]
Total shares reserved	11,556,789	10,338,814
Options Available for Future Grants
Class Of Stock [Line Items]
Total shares reserved	3,032,820	2,820,341
Pre-funded warrants issued and outstanding
Class Of Stock [Line Items]
Total shares reserved	4,000,000	4,000,000
2019 Equity Incentive Plan and 2015 Stock Plan \| Options Issued and Outstanding
Class Of Stock [Line Items]
Total shares reserved	4,099,947	2,993,280
2019 Equity Incentive Plan \| Restricted Stock Units Issued and Outstanding
Class Of Stock [Line Items]
Total shares reserved	13,500	27,000
2019 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total shares reserved	410,522	498,193

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details