COMPASS Pathways (CMPS) 10-K 29 Feb 24 2023 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Feb. 23, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2023
Document Transition Report	false
Entity File Number	001-39522
Entity Registrant Name	COMPASS Pathways plc
Entity Incorporation, State or Country Code	X0
Entity Address, Address Line One	33 Broadwick Street
Entity Address, City or Town	London
Entity Address, Postal Zip Code	W1F 0DQ
Entity Address, Country	GB
City Area Code	716
Local Phone Number	676-6461
Title of 12(b) Security	American Depositary Shares, each representing one ordinary share, par value of £0.008 per share
Trading Symbol	CMPS
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 215.7
Entity Common Stock, Shares Outstanding		64,227,371
Documents Incorporated by Reference	Portions of the Registrant’s Proxy Statement for the 2024 Annual Meeting of Shareholders are incorporated herein by reference into Part III of this Annual Report on Form 10-K to the extent stated herein. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the Registrant’s fiscal year ending December 31, 2023.
Entity Central Index Key	0001816590
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Auditor Information [Abstract]
Auditor Firm ID	876
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Reading, United Kingdom

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
CURRENT ASSETS:
Cash and cash equivalents	$ 220,198	$ 143,206
Restricted cash	440	175
Prepaid income tax	1,123	575
Prepaid expenses and other current assets	39,535	47,695
Total current assets	261,296	191,651
NON-CURRENT ASSETS:
Operating lease right-of-use assets	4,306	2,006
Deferred tax assets	3,336	2,224
Long-term prepaid expenses and other assets	7,049	1,413
Total assets	275,987	197,294
CURRENT LIABILITIES:
Accounts payable	5,892	4,761
Accrued expenses and other liabilities	11,301	9,325
Operating lease liabilities - current	2,411	1,510
Total current liabilities	19,604	15,596
NON-CURRENT LIABILITIES
Long-term debt	28,757	0
Operating lease liabilities - non-current	1,882	418
Total liabilities	50,243	16,014
Commitments and contingencies (Note 12)
SHAREHOLDERS' EQUITY:
Additional paid-in capital	621,645	458,825
Accumulated other comprehensive loss	(16,926)	(16,867)
Accumulated deficit	(379,610)	(261,146)
Total shareholders' equity	225,744	181,280
Total liabilities and shareholders' equity	275,987	197,294
Ordinary shares
SHAREHOLDERS' EQUITY:
Ordinary and deferred shares	635	440
Deferred Shares
SHAREHOLDERS' EQUITY:
Ordinary and deferred shares	$ 0	$ 28

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - £ / shares	Dec. 31, 2023	Dec. 31, 2022
Ordinary shares
Common stock, par value (in GBP per share)	£ 0.008	£ 0.008
Common stock, authorized (in shares)	61,943,471	42,631,794
Common stock, issued (in shares)	61,943,471	42,631,794
Common stock, outstanding (in shares)	61,943,471	42,631,794
Deferred Shares
Common stock, par value (in GBP per share)	£ 21,921.504	£ 21,921.504
Common stock, authorized (in shares)	0	1
Common stock, issued (in shares)	0	1
Common stock, outstanding (in shares)	0	1

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
OPERATING EXPENSES:
Research and development	$ 87,518	$ 65,053	$ 44,027
General and administrative	49,401	45,350	39,194
Total operating expenses	136,919	110,403	83,221
LOSS FROM OPERATIONS:	(136,919)	(110,403)	(83,221)
OTHER INCOME (EXPENSE), NET:
Other income	4,878	4,061	40
Interest expense	(2,204)	0	0
Foreign exchange gains	3,686	821	1,990
Benefit from R&D tax credit	12,875	14,424	9,648
Total other income, net	19,235	19,306	11,678
Loss before income taxes	(117,684)	(91,097)	(71,543)
Income tax expense	(780)	(408)	(199)
Net loss	$ (118,464)	$ (91,505)	$ (71,742)
Net loss per share attributable to ordinary shareholders - basic (in dollars per share)	$ (2.32)	$ (2.16)	$ (1.79)
Net loss per share attributable to ordinary shareholders - diluted (in dollars per share)	$ (2.32)	$ (2.16)	$ (1.79)
Weighted average ordinary shares outstanding - basic (in shares)	51,028,024	42,436,292	39,997,587
Weighted average ordinary shares outstanding - diluted (in shares)	51,028,024	42,436,292	39,997,587
Other comprehensive loss:
Foreign exchange translation adjustment	$ (59)	$ (25,707)	$ (5,745)
Comprehensive loss	$ (118,523)	$ (117,212)	$ (77,487)

Consolidated Statements of Shar

Consolidated Statements of Shareholders’ Equity - USD ($) $ in Thousands	Total	At-The-Market Offering	Private Investment In Public Entity Offering	2020 Award	ADDITIONAL PAID-IN CAPITAL	ADDITIONAL PAID-IN CAPITAL At-The-Market Offering	ADDITIONAL PAID-IN CAPITAL Private Investment In Public Entity Offering	ADDITIONAL PAID-IN CAPITAL 2020 Award	ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	ACCUMULATED DEFICIT	ORDINARY SHARES	ORDINARY SHARES COMMON STOCK	ORDINARY SHARES COMMON STOCK At-The-Market Offering	ORDINARY SHARES COMMON STOCK Private Investment In Public Entity Offering	ORDINARY SHARES COMMON STOCK 2020 Award	DEFERRED SHARES	DEFERRED SHARES COMMON STOCK
Beginning balance (in shares) at Dec. 31, 2020												35,930,331					1
Beginning balance at Dec. 31, 2020	$ 196,561				$ 279,480				$ 14,585	$ (97,899)		$ 367					$ 28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of share options (in shares)											1,476,936	1,244,709
Exercise of share options	1,905				1,891							$ 14
Issuance of ordinary shares under ATM facility or PIPE offering, net of issuance costs (in shares)												4,600,000			232,227
Issuance of ordinary shares under ATM facility or PIPE offering, net of issuance costs (in shares)	154,794			$ 0	154,743			$ (3)				$ 51			$ 3
Issuance of ordinary shares to settle vested restricted stock units (in shares)											12,607	12,607
Share-based compensation expense	8,639				8,639
Unrealized loss on foreign currency translation	(5,745)								(5,745)
Net loss	(71,742)									(71,742)
Ending balance (in shares) at Dec. 31, 2021												42,019,874					1
Ending balance at Dec. 31, 2021	284,412				444,750				8,840	(169,641)		$ 435					$ 28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of share options (in shares)											462,722	462,722
Exercise of share options	401				397							$ 4
Issuance of ordinary shares under ATM facility or PIPE offering, net of issuance costs (in shares)												44,416
Issuance of ordinary shares under ATM facility or PIPE offering, net of issuance costs (in shares)	440				439							$ 1
Issuance of ordinary shares to settle vested restricted stock units (in shares)											24,747	82,622
Issuance of ordinary shares under employee share purchase plan (in shares)												22,160
Issuance of ordinary shares under employee share purchase plan	199				199
Shares tendered for withholding taxes	83				83
Share-based compensation expense	13,123				13,123
Unrealized loss on foreign currency translation	(25,707)								(25,707)
Net loss	(91,505)									(91,505)
Ending balance (in shares) at Dec. 31, 2022											42,631,794	42,631,794				1	1
Ending balance at Dec. 31, 2022	$ 181,280				458,825				(16,867)	(261,146)		$ 440					$ 28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of share options (in shares)	166,801										166,801	166,801
Exercise of share options	$ 2											$ 2
Issuance of ordinary shares under ATM facility or PIPE offering, net of issuance costs (in shares)													2,937,622	16,076,750
Issuance of ordinary shares under ATM facility or PIPE offering, net of issuance costs (in shares)		$ 28,120	$ 116,815			$ 28,091	$ 116,652						$ 29	$ 163
Issuance of warrants to purchase ordinary shares	687				687
Issuance of ordinary shares to settle vested restricted stock units (in shares)											69,120	78,022
Issuance of ordinary shares to settle vested restricted stock units	0				(1)							$ 1
Cancellation of deferred share (in shares)																	(1)
Cancellation of deferred share	0				28												$ (28)
Issuance of ordinary shares under employee share purchase plan (in shares)												52,482
Issuance of ordinary shares under employee share purchase plan	351				351
Shares tendered for withholding taxes	265				265
Share-based compensation expense	17,277				17,277
Unrealized loss on foreign currency translation	(59)								(59)
Net loss	(118,464)									(118,464)
Ending balance (in shares) at Dec. 31, 2023											61,943,471	61,943,471				0	0
Ending balance at Dec. 31, 2023	$ 225,744				$ 621,645				$ (16,926)	$ (379,610)		$ 635					$ 0

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders’ Equity (Deficit) (Parenthetical) - £ / shares	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Aug. 31, 2020
ORDINARY SHARES
Common stock, par value (in GBP per share)	£ 0.008	£ 0.008	£ 0.008	£ 0.008	£ 0.008	£ 0.001
DEFERRED SHARES
Common stock, par value (in GBP per share)	£ 21,921.504	£ 21,921.504	£ 21,921.504	£ 21,921.504	£ 21,921.504

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (118,464)	$ (91,505)	$ (71,742)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	242	330	175
Non-cash interest	636	0	0
Loss on disposal of property and equipment	40	0	0
Non-cash (gain) loss on foreign currency remeasurement	(2,617)	1,141	22
Non-cash share-based compensation	17,277	13,123	8,639
Non-cash lease expenses	2,027	2,126	1,797
Changes in operating assets and liabilities
Prepaid expenses and other current assets	10,458	(28,760)	(8,984)
Deferred and prepaid tax assets	(1,661)	(1,701)	(877)
Long-term prepaid expenses and other assets	(5,842)	(307)	(160)
Operating lease liabilities	(1,959)	(2,081)	(1,880)
Accounts payable	864	2,497	(163)
Accrued expenses and other liabilities	1,623	(314)	5,428
Net cash used in operating activities	(97,376)	(105,451)	(67,745)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(66)	(596)	(334)
Proceeds from disposal of property and equipment	2	0	0
Net cash used in investing activities	(64)	(596)	(334)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of ordinary shares, net of issuance costs	144,935	440	154,794
Proceeds from the issuance of shares under the employee share purchase plan	351	199	0
Payments of withholding tax on stock award	(265)	0	0
Net proceeds from issuance of long-term debt	29,585	0	0
Payment of issuance cost of long-term debt	(778)	0	0
Proceeds from exercise of share options	2	401	1,852
Net cash provided by financing activities	173,830	1,040	156,646
Effect of exchange rate changes on cash, cash equivalents and restricted cash	867	(24,959)	(5,576)
Net increase/(decrease) in cash, cash equivalents and restricted cash	77,257	(129,966)	82,991
Cash, cash equivalents and restricted cash, beginning of the period	143,381	273,347	190,356
Cash, cash equivalents and restricted cash, end of the period	220,638	143,381	273,347
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid for interest	1,254	0	0
SUPPLEMENTAL NON-CASH TRANSACTIONS:
Right-of-use assets obtained in exchange for new operating lease liabilities	4,184	783	5,562
Unpaid withholding tax on stock award recognized in accrued and other liabilities	0	85	0
Proceeds from exercise of options received and recorded in other current assets	0	0	53
Deferred issuance costs included in accrued expenses	0	0	856
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	220,198	143,206	273,243
Short-term restricted cash	440	175	104
Total cash, cash equivalents and restricted cash	220,638	143,381	273,347
Long-term Debt Issuance
SUPPLEMENTAL NON-CASH TRANSACTIONS:
Issuance of warrants	687	0	0
Ordinary Shares Issuance
SUPPLEMENTAL NON-CASH TRANSACTIONS:
Issuance of warrants	$ 2,011	$ 0	$ 0

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business Compass Pathways plc, or the Company, is a biotechnology company dedicated to accelerating patient access to evidence-based innovation in mental health. The Company is developing its investigational COMP360 psilocybin treatment through late-stage clinical trials in Europe and North America for patients with treatment-resistant depression. The Company is subject to risks and uncertainties common to clinical stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary intellectual property and technology, compliance with government regulations and the ability to secure additional capital to fund operations. Therapeutic candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s therapeutic development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from sales. The Company has funded its operations primarily with proceeds from the sale of its convertible preferred shares, the issuance of convertible notes, and through the sale of American Depository Shares, or ADSs, in connection with the Company’s initial public offering, or the IPO, in September 2020, and its May 2021 follow-on offering. On October 8, 2021, the Company entered into a Sales Agreement with Cowen and Company, LLC, or Cowen, under which the Company may issue and sell from time to time up to $150.0 million of its ADSs, each representing one ordinary share, through Cowen as the sales agent. Sales of the Company’s ADSs, if any, will be made at market prices. Through December 31, 2023, the Company sold 2,982,038 ADSs under the Sales Agreement, resulting in $28.6 million in net proceeds. On June 30, 2023 (the “Effective Date”), the Company entered into a Loan Agreement with Hercules, which provided for aggregate maximum borrowings of up to $50.0 million, including a term loan of $30.0 million, which was funded on the Effective Date. On August 16, 2023, the Company entered into a Securities Purchase Agreement, pursuant to which the Company agreed to sell and issue in a private placement transaction (the “PIPE”) (i) 16,076,750 ADSs and (ii) PIPE Warrants to purchase up to 16,076,750 ADSs, at a purchase price of approximately $7.78 per ADS and accompanying PIPE Warrant to purchase one ADS. Each PIPE Warrant has an exercise price of $9.93 per ADS and is exercisable for a three year period beginning in February 2024. The PIPE Warrants may be exercised on a cashless basis if there is no effective registration statement registering the shares underlying the PIPE Warrants. The Company has incurred recurring losses since its inception, including net losses of $118.5 million and $91.5 million for the years ended December 31, 2023 and 2022, respectively. In addition, as of December 31, 2023, the Company had an accumulated deficit of $379.6 million. The Company expects to continue to generate operating losses for the foreseeable future. The Company believes the cash and cash equivalents on hand as of December 31, 2023 of $220.2 million, together with the net proceeds raised to date during the first quarter, will be sufficient to fund its operating expenses and capital expenditure requirements into late 2025. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. The Company’s inability to raise capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies. There can be no assurance that the current operating plan will be achieved or that additional funding will be available on terms acceptable to the Company, or at all. The Company may raise additional capital through a combination of equity offerings, debt financings, collaborations, and other strategic transactions, including marketing, distribution or licensing arrangements. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial conditions. Market volatility, instability in the banking system, geopolitical tensions resulting from the ongoing war between Ukraine and Russia, the Israel-Hamas war, fluctuating inflation and interest rates and the related impact on U.S., U.K. and global economies, the risk of economic slowdown or recession or a potential government shutdown in the United States, the upcoming presidential election the United States or other factors could adversely impact our operations, financial results and ability to raise additional funding.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America, or U.S. GAAP. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated on 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 reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of income and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, research and development expenses and the research and development tax credit. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments that have maturities of three months or less when acquired to be cash equivalents. The Company does not currently have any material cash equivalents. Restricted Cash Restricted cash as of December 31, 2023 and 2022 represents a collateral deposit for employee credit cards. Investment The Company’s investment of $0.5 million to acquire 8% (on a fully diluted basis) shareholding in Delix Therapeutics, Inc., does not have a readily determinable fair value and it is carried at cost, less impairment, adjusted for subsequent changes to estimated fair value up to the original cost, in circumstances where the Company does not have the ability to exercise significant influence or control over the operating and financial policies of the investee. As of December 31, 2023, no impairment loss was recognized. Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under U.S. GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the inputs for the first two are considered observable and the inputs for the last are considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques The carrying amounts reflected in the consolidated balance sheets for the Company’s cash and cash equivalents, restricted cash, accounts payable and accrued expenses approximate fair value because of the short-term nature of these instruments. Concentration of Credit Risk Financial instruments that subject the Company to credit risk consist primarily of cash and cash equivalents. The Company places cash and cash equivalents in diversified and established financial institutions. Accounts at each institution are insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000. The Company has cash and cash equivalents in excess of the FDIC insured limit. The Company has no significant off-balance-sheet risk or concentration of credit risk, such as foreign exchange contracts, options contracts, or other foreign hedging arrangements. Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Estimated Useful Life Lab equipment 5 years Office equipment 3-5 years Furniture and fixtures 3 years Leasehold improvements Shorter of useful life or remaining lease term Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the consolidated statements of operations and comprehensive loss. Expenditures for repairs and maintenance are charged to expense as incurred. Impairment of Long-Lived Assets The Company evaluates assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses or had triggering events related to its underlying assets for the years ended December 31, 2023 and 2022. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage its business as a single operating segment, which carries out its operations in two geographic regions: the United Kingdom, or UK, and the United States. The Company’s property and equipment are primarily located in the UK. The Company’s singular concentration is focused on accelerating patient access to evidence-based innovation in mental health. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, share-based compensation and benefits, travel, and external costs of outside vendors engaged to conduct clinical development activities, clinical trials and the cost to manufacture clinical trial materials. Research Contract Costs, Prepayments and Accruals The Company has entered into various research and development-related contracts with research institutions and other companies. These agreements are generally cancellable, and related payments are recorded as research and development expenses as incurred. The Company records prepayments and accruals for estimated ongoing research costs and receives updated estimates of costs and amounts owed on a monthly basis from its third-party service providers. When evaluating the adequacy of the prepayments and accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted cost estimates from third-party service providers. Estimates are made in determining the prepaid and accrued balances at the end of any reporting period. The Company considers any prepayment that is more than 12 months in advance of the associated expense to be long-term. Actual results could differ from the Company’s estimates. The Company’s historical prepayments and accrual estimates have not been materially different from the actual costs. Share-Based Compensation The Company accounts for all share-based payment awards granted to employees and non-employees as share-based compensation expense at fair value. The Company grants equity awards under its share-based compensation programs, which may include share options and restricted share units. The measurement date for employee and non-employee awards is the date of grant, and share-based compensation costs are recognized as an expense over the requisite service period, which is the vesting period, on a straight-line basis. Share-based compensation expense is classified in the accompanying consolidated statements of operations and comprehensive loss based on the function to which the related services are provided. The Company recognizes share-based compensation expense for the portion of awards that have vested. Forfeitures are recorded as they occur. On October 1, 2021, the Company launched the Share Incentive Plan, or the SIP, and Employee Share Purchase Plan, or the ESPP, through which employees can purchase shares at a discounted price. The Company estimates the fair value of stock options and shares to be issued under the SIP and ESPP using the Black-Scholes option-pricing model on the date of grant. The fair value of shares to be issued under these plans are recognized and amortized on a straight-line basis over the purchase period, which is generally six months. There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 8 for the Company’s assumptions used in connection with option grants made during the periods covered by these consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility . The Company lacks sufficient company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The Company utilizes this method due to the lack of historical exercise data and the plain nature of its share-based awards. Risk-free interest rate . The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. In addition, the Loan Agreement with Hercules currently prohibits dividends that may be declared or paid on our ordinary shares. Fair value of ordinary shares. The fair value of ordinary shares is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the day prior to or day of the grant. Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and current and non-current lease liabilities, as applicable. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets and to allocate all the contract consideration to the lease component only. All the Company’s leases are classified as operating leases. Lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. When readily determinable, the discount rate used to calculate the lease liability is the rate implicit in the lease. As the Company’s leases do not typically provide an implicit rate, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. As the Company does not have a rating agency-based credit rating, quotes were obtained from lenders to establish an estimated secured rate to borrow based on Company and market-based factors as of the respective lease measurement dates. The Company has elected not to recognize leases with an original term of one year or less on the balance sheets. The Company typically only includes the non-cancelable lease term in its assessment of a lease arrangement unless there is an option to extend the lease that is reasonably certain of exercise. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date. Operating lease costs are recognized on a straight-line basis over the lease term, and they are categorized within research and development and general and administrative expenses in the consolidated statements of operations and comprehensive loss. The operating lease cash flows are categorized under net cash used in operating activities in the consolidated statements of cash flows. Foreign Currency Translation The functional currency is the currency of the primary economic environment in which an entity’s operations are conducted. On January 1, 2023, Compass Pathways plc and its wholly owned subsidiary Compass Pathfinder Holdings Limited changed their functional currency to the U.S. dollar. Compass Pathways plc and Compass Pathfinder Holdings Limited have no operating activities and their primary functions are to serve as a financing vehicle to fund the operations of the Company’s operating entities, to serve as the listing company needed to access U.S. capital markets, and to hold investments. Therefore, its financing source is the primary indicator of its cash flows and its functional currency. The change in functional currency from the British Pound Sterling is due to a change in the source of the Company’s financing and cash flows going forward, which will now primarily be U.S. Dollars (“USD”). The functional currency of Compass Pathfinder Holdings Limited’s wholly owned non-U.S. subsidiary, Compass Pathfinder Limited, is British Pound Sterling and the functional currency of its U.S. subsidiary, Compass Pathways Inc. is USD. The functional currency of these subsidiaries is the same as the local currency. The translated balances of monetary and non-monetary assets and liabilities recorded in the reporting entity’s consolidated financial statements as of the end of the prior reporting period become the new accounting basis for those assets and liabilities in the period of the change. To the extent that the distinct and separable operation has monetary assets and liabilities denominated in the old functional currency, such balances will create transaction gains and losses subsequent to the change in functional currency. The balance recorded in the cumulative translation adjustment account for prior periods is not reversed upon the change in functional currency. The Company translates the assets and liabilities of Compass Pathfinder Limited into USD at the exchange rate in effect on the balance sheet date. Income and expenses are translated at the average exchange rate in effect during the period. Unrealized translation gains and losses are recorded as a cumulative translation adjustment, which is included in the consolidated statements of shareholders’ equity as a component of accumulated other comprehensive income/(loss). Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in its tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that deferred tax assets will be recovered in the future to the extent management believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more- likely-than-not to be sustained, the tax position is then assessed as the amount of benefit to recognize in the consolidated financial statements. The amount of benefit that may be used is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate, as well as the related net interest and penalties. As of December 31, 2023 and 2022, the Company has not identified any material uncertain tax positions. The Company recognizes interest and penalties related to unrecognized tax benefits on the income tax expense line in the accompanying consolidated statements of operations and comprehensive loss. As of December 31, 2023 and 2022 no accrued interest or penalties are included on the related tax liability line in the consolidated balance sheets. Benefit from Research and Development Tax Credit As a company that carries out extensive research and development activities, the Company benefits from the UK research and development tax credit regime under the scheme for small or medium-sized enterprises, or SME. Under the SME regime, in effect through December 31, 2023, the Company is able to surrender some of its trading losses that arise from qualifying research and development activities for a cash rebate of a portion of such qualifying research and development expenditure. Up until April 1, 2023 the effective rate was 33.3% on in-house expenditures and 21.7% on work that was contracted out (to unconnected subcontractors). On and after April 1, 2023, the effective rates reduced to 18.6% and 12.1%, respectively. New rules were announced in the Finance Bill 2023-24 for an enhanced effective rate of relief for loss making research intensive SMEs, which would be 27.0% for qualifying in-house expenditures and 17.5% for qualifying subcontracted expenditures. The legislation was not substantively enacted at the balance sheet date, although based on the proposed rules, the Company does not believe that it would meet the criteria for the enhanced rate of relief for the year through December 31, 2023. After the Finance Bill has received Royal Assent, the R&D claim will be reviewed at a transaction level, and the threshold calculation prepared with more certainty to determine whether the enhanced rate can be applied for submission of the claim. The Company currently meets the conditions of the SME regime. A large portion of costs relating to research and development, clinical trials and manufacturing activities are eligible for inclusion within these tax credit cash rebate claims. The Company is subject to corporate taxation in the UK. Due to the nature of the business, the Company has generated losses since inception. The benefit from research and development, or R&D, tax credits is recognized in the consolidated statements of operations and comprehensive loss as a component of other income, net, and represents the sum of the research and development tax credits recoverable in the UK. The UK research and development tax credit is fully refundable to the Company and is not dependent on current or future taxable income. As a result, the Company has recorded the entire benefit from the UK research and development tax credit as a benefit which is included in net loss before income tax and accordingly, not reflected as part of the income tax provision. If, in the future, any UK research and development tax credits generated are needed to offset a corporation tax liability in the UK, that portion would be recorded as a benefit within the income tax provision and any refundable portion not dependent on taxable income would continue to be recorded within other income, net. The Company may not be able to continue to claim research and development tax credits under the SME regime in the future because it may no longer qualify as a small or medium-sized company. In addition, there is a maximum cap in respect of a given project of €7.5 million which may impact the Company’s ability to claim R&D tax credits in future. Further, the U.K. Finance Act of 2021 introduced a cap on credit claims under the SME Program in excess of £20,000 with effect from April 2021 by reference to, broadly, three times the total Pay As You Earn, or PAYE, and National Insurance Contributions, or NICs, liability of the company, subject to an exception which prevents the cap from applying. That exception requires the company to be creating, taking steps to create or managing intellectual property, as well as having qualifying research and development expenditure in respect of connected parties, which does not exceed 15% of the total claimed. If such exception does not apply, this could restrict the amount of payable credit that the Company claims. Unsurrendered UK losses may be carried forward indefinitely to be offset against future taxable profits, subject to numerous utilization criteria and restrictions. The amount that can be offset each year is limited to £5.0 million plus an incremental 50% of UK taxable profits. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in shareholders’ equity that result from transactions and economic events other than those with shareholders. For the years ended December 31, 2023 and 2022, the only component of accumulated other comprehensive loss is foreign currency translation adjustment. Net Loss per Share The Company has reported losses since inception and has computed basic net loss per share attributable to ordinary shareholders by dividing net loss attributable to ordinary shareholders by the weighted-average number of ordinary shares outstanding for the period, without consideration for potentially dilutive securities. The Company computes diluted net loss per ordinary share after giving consideration to all potentially dilutive ordinary shares, including unvested restricted shares, outstanding options and warrants. Because the Company has reported net losses since inception, these potential ordinary shares have been anti-dilutive and basic and diluted loss per share were the same for all periods presented. Derivatives The Company enters into foreign currency contracts to reduce the risk that its cash flows and earnings will be adversely affected by foreign currency exchange rate fluctuations. The Company does not enter into foreign currency contracts for speculative purposes. The Company recognizes derivative instruments, which do not qualify for hedge accounting, as either assets or liabilities on the balance sheet at fair value. The Company records changes in the fair value (gains or losses) of the derivatives in the accompanying consolidated statements of operations and comprehensive loss as other income, net. The Company did not enter into any contracts during the year ended December 31, 2023. During the year ended December 31, 2022, the Company entered into and settled a foreign forward agreement, resulting in a positive fair value change of $2.3 million in other income. During the year ended December 31, 2021, the Company did not enter into any contracts. Long-term Debt On June 30, 2023, the Company entered into the Loan Agreement with Hercules. The Company assessed all terms and features of the Loan Agreement in order to identify any potential embedded features that would require bifurcation. As part of this analysis, the Company assessed the economic characteristics and risks of the debt. The Company determined that all features of the Loan Agreement are clearly and closely associated with a debt host and, as such, do not require separate accounting as a derivative liability. Debt issuance costs consist of costs incurred in obtaining long-term financing. These costs are classified on the consolidated balance sheet as a direct deduction from the carrying amount of the related debt liability. These expenses are deferred and amortized as part of interest expense in the consolidated statement of operations using the effective interest rate method over the term of the debt agreement. Warrants On June 30, 2023, the Company entered into a warrant agreement with Hercules. The Company assessed all terms and features of the Warrant Agreement in order to determine accounting classification of the warrants as equity or liability. As part of this analysis, the Company determined it appropriate to account for the warrants issued under the Loan Agreement as equity. On August 18, 2023, in connection with the PIPE, the Company issued and sold PIPE Warrants to purchase up to 16,076,750 ADSs, each representing one ordinary share, at an exercise price of $9.93 per ADS. The PIPE Warrants are exercisable for a three year period beginning in February 2024. The Company assessed all terms and features of the PIPE Warrant Agreement in order to determine accounting classification of the warrants as equity or liability. As part of this analysis, the Company determined it appropriate to account for the PIPE Warrants as equity. The Company measures warrants at inception at fair value using the Black-Scholes valuation model. Assumptions used in the warrant pricing model include the following: Expected volatility . The Company lacks sufficient company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Hercules warrants is ten years. The expected term of the PIPE Warrants is three and a half years. Risk-free interest rate . The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of the issuance for time periods that are approximately equal to the expected term of the warrant. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. In addition, the Loan Agreement with Hercules currently prohibits, and any future debt financing arrangements may contain terms prohibiting or limiting the number of dividends that may be declared or paid on our ordinary shares. Fair value of ordinary shares. The fair value of the warrants is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the day of issuance. Recently Issued Accounting Pronouncements In November 2023, the Financial Accounting Standard Board ("FASB") issued new guidance designed to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant expenses per segment. The guidance is effective for all fiscal years beginning after December 15, 2023, and for interim periods beginning after December 15, 2024. The new standard must be adopted on a retrospective basis and early adoption is permitted. The Company is not early adopting the standard. We are currently evaluating this guidance to determine its impact on our consolidated financial statements. In December 2023, the FASB issued new guidance designed to improve income tax disclosure requirements, primarily through increased disaggregation disclosures within the effective tax rate reconciliation as well as enhanced disclosures on income taxes paid. The guidance is effective for all fiscal years beginning after December 15, 2024. The new standard can be adopted on a prospective basis with an option to be adopted retrospectively and early adoption is permitted. The Company is not early adopting the standard. We are currently evaluating this guidance to determine its impact on our consolidated financial statements.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2023 2022 UK R&D tax credit $ 27,877 $ 13,972 Prepaid insurance premium 1,885 2,818 Prepaid research and development 6,826 28,211 VAT recoverable 1,052 1,652 Other current assets 1,895 1,042 $ 39,535 $ 47,695

Long-term Prepaid Expenses and

Long-term Prepaid Expenses and Other Assets	12 Months Ended
	Dec. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Long-term Prepaid Expenses and Other Assets	Long-term Prepaid Expenses and Other Assets Long-term prepaid expenses and other assets consisted of the following (in thousands): December 31, 2023 2022 Prepaid research and development - long-term 5,955 — Property and equipment 423 617 Other investment 469 469 Other assets 202 327 $ 7,049 $ 1,413

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	12 Months Ended
	Dec. 31, 2023
Other Liabilities Disclosure [Abstract]
Accrued Expenses and Other Liabilities	Accrued Expenses and Other Liabilities Accrued expenses and other liabilities consisted of the following (in thousands): December 31, 2023 2022 Accrued research and development expense $ 2,117 $ 1,684 Accrued professional expenses 1,077 1,284 Accrued compensation and benefit costs 7,069 5,534 Payroll tax payable 13 167 Other liabilities 1,025 656 $ 11,301 $ 9,325

Debt

Debt	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Debt	Debt On June 30, 2023, the Company entered into the Loan Agreement with Hercules, which provided for aggregate maximum borrowings of up to $50.0 million, consisting of (i) a term loan of $30.0 million, which was funded on the Effective Date, (ii) subject to the Company achieving certain performance milestones and available until December 15, 2024, an additional term loan of $10.0 million, and (iii) subject to the approval of Hercules’ investment committee in its sole discretion, and available during the interest-only period, an additional term loan of $10.0 million. The term loan will mature on July 1, 2027. The outstanding principal balance of the term loan bears interest at an annual rate equal to the greater of either (i) the prime rate as reported in The Wall Street Journal plus 1.50% or (ii) 9.75%. Accrued interest is payable monthly following the funding of each term loan. In addition to accrued interest, payment-in-kind (PIK) interest of 1.40% will be added to the balance of the loan. Payments under the Loan Agreement are interest only until the first principal payment is due on July 1, 2025 (or if the Borrowers achieve certain performance milestones, the interest only period may be extended to January 2, 2026 and, upon the achievement of certain additional performance milestones, the interest only period may be extended to July 1, 2026), followed by equal monthly payments of principal and interest through the scheduled maturity date, July 1, 2027. The Company incurred fees and transaction costs totaling $3.3 million associated with the initial term loan, which are recorded as a reduction to the carrying value of the long-term debt in the consolidated balance sheet. These fees included $0.4 million of facility fees, $0.8 million of company fees, $0.7 million in warrants, and $1.4 million of end of term charges. The fees, transaction costs, and the end of term charge are amortized to interest expense through the maturity date using the effective interest method. The effective interest rate of the Loan Agreement was 15.8% as of December 31, 2023. The Company issued warrants to Hercules to purchase the Company’s Ordinary Shares equal to the quotient derived by dividing (i) the amount equal to (a) 2.5% times (b) the aggregate principal amount of term loan advances made and funded under the Loan Agreement by (ii) the exercise price of the warrants. Upon receipt of the first term loan, 94,222 shares became exercisable to Hercules with a fair market value of $0.7 million. The Loan Agreement includes a financial covenant requiring us to maintain a minimum level of $22.5 million of cash during the period commencing on July 1, 2024 (subject to adjustment if certain performance milestones are met). If the Company meets the performance milestones, the minimum cash covenant will not apply if its market capitalization is at least $750.0 million. The Company was in compliance with all covenants of the Loan Agreement as of December 31, 2023. Long-term debt consisted of the following (in thousands): December 31, 2023 Term loan payable $ 30,000 End of term charge 1,425 Future principal payments and end of term charge $ 31,425 PIK interest payable 216 Unamortized debt issuance costs (2,884) Carrying value of long-term debt $ 28,757 Future principal payments, including End of Term Charge, are as follows (in thousands): December 31, 2024 — December 31, 2025 6,572 December 31, 2026 14,166 December 31, 2027 10,687 Total $ 31,425

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity Ordinary Shares On May 4, 2021, the Company sold 4,000,000 ordinary shares in connection with its follow-on offering. On May 19, 2021 the underwriters exercised their option to purchase an additional 600,000 ordinary shares. This capital raise resulted in net proceeds of approximately $154.8 million after deducting underwriting fees and offering costs. Each ordinary share entitles the holder to one vote on all matters submitted to a vote of the Company’s shareholders. Ordinary shareholders are entitled to receive dividends, if any, as may be declared by the board of directors. Through December 31, 2023 , no cash dividends had been declared or paid by the Company. On October 8, 2021, the Company entered into a Sales Agreement with Cowen and Company, LLC, or Cowen, under which the Company may issue and sell from time to time up to $150.0 million of its ADSs, each representing one ordinary share, through Cowen as the sales agent. Sales of the Company’s ADSs, if any, will be made at market prices. Through December 31, 2023, we sold 2,982,038 ADSs, resulting in $28.6 million in net proceeds. During the years ended December 31, 2023, 2022 and 2021 , the Company issued ordinary shares in the amount of 166,801, 462,722 and 1,476,936, respectively, to settle share options exercised by employees and non-employees. During the year ended December 31, 2023, a total of 96,177 restricted share units vested, of which 69,120 shares were issued and 27,057 shares were settled. During the year ended December 31, 2023, a total of 78,022 ordinary shares were issued in settlement of restricted share units, of which 8,902 shares were vested and not issued at December 31, 2022. During the year ended December 31, 2022, a total of 42,635 restricted share units vested, of which 24,747 shares were vested and issued in settlement, 8,902 shares were vested but had not been issued and 8,986 shares were settled at December 31, 2022. During the year ended December 31, 2022, a total of 82,622 shares were issued in settlement, of which 57,875 vested in 2021 and 24,747 vested in 2022. During the year ended December 31, 2021, a total of 70,482 restricted share units vested, of which 12,607 shares were vested and issued in settlement and 57,875 shares were vested but had not been issued at December 31, 2021. During the years ended December 31, 2023, 2022, and 2021 the Company issued in total 52,482, 22,160 and nil shares, respectively, under the employee share purchase plan. Deferred Shares Immediately prior to the completion of the Company’s IPO in September 2020, the different classes of issued share capital of Compass Pathways plc were reorganized by way of a reverse share split, which was retroactively restated in our consolidated financial statements. As part of this reverse share split, the nominal value of Compass Pathways plc’s ordinary shares changed from £0.001 per share to £0.008 per share and a single, non-voting deferred share with a nominal value of £21,921.504 in the capital of the Company was created and transferred to the Company. On June 28, 2023, the single deferred share was cancelled. Warrants On June 30, 2023, the Company entered into a Warrant Agreement with Hercules, which provides Hercules with the right to purchase a number of shares of the Company’s Ordinary Shares equal to the quotient derived by dividing (i) the amount equal to (a) 2.5% times (b) the aggregate principal amount of term loan advances made and funded under the Loan Agreement by (ii) the exercise price. Upon receipt of each term loan, the Warrant will automatically become exercisable and will expire in 10 years (on June 30, 2033). On June 30, 2023, with the receipt of the first term loan, 94,222 shares became exercisable to Hercules with a fair market value of $0.7 million. On August 18, 2023, in connection with the PIPE, the Company issued and sold warrants to purchase up to 16,076,750 ADSs, each representing one ordinary share, at a purchase price of $9.93 per ADS. The PIPE Warrants will become exercisable for a three year period beginning in February 2024.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Share-Based Compensation	Share-Based Compensation 2017 Equity Incentive Plan Under the Company’s historical shareholder and subscription agreements, the Company was authorized to issue restricted shares, restricted share units, as well as options, as incentives to its employees, non-employees and members of its board of directors. To the extent such incentives were in the form of share options, the options were granted pursuant to the terms of the 2017 Equity Incentive Plan, or the 2017 Plan. In July 2019, the Company’s board of directors adopted the 2017 Plan. The 2017 Plan provided for the grant of Enterprise Management Incentive, or EMI, options, to its UK employees, for the grant of options to its U.S. employees and non-employees of the Company. The 2017 Plan was administered by the board of directors. Options granted under the 2017 Plan, typically vest over a three The options granted on June 30, 2020 were subject to 25% vesting upon the earlier occurrence of (i) the one year anniversary of the date of grant, or (ii) the date of the listing of the Company's ordinary shares on any stock exchange, followed by straight line vesting for three years for the remaining 75% of the allocation until vested in full. The restricted share units granted on June 30, 2020 were subject to 25% vesting upon the earlier of (i) the one year anniversary of the date of grant, or (ii) the first day following the six-month anniversary of the listing of the Company's ordinary shares on any stock exchange on which the closing price of the shares is 20% higher than the listing price for at least five consecutive trading days. As of December 31, 2023, the Company was authorized to issue a total of 1,437,252 ordinary shares underlying outstanding options granted under the 2017 Plan prior to the IPO. 2020 Employee Share Purchase Plan The Company’s 2020 Employee Share Purchase Plan, or the ESPP, was adopted by the Board in September 2020 and approved by shareholders in September 2020 and became effective upon the effectiveness of the Company’s Registration Statement on Form F-1 in connection with the IPO. The ESPP initially reserved and authorized the issuance of up to a total of 340,053 ordinary shares to participating employees. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2022 and each January 1 thereafter through termination of the 2020 Plan, by the lesser of (i) 1% of the outstanding number of ordinary shares on the immediately preceding December 31, (ii) 510,080 ordinary shares or (iii) such lesser number of ordinary shares as determined by the plan administrator. The number of shares reserved under the ESPP is subject to change in the event of a share split, share dividend or other change in our capitalization. On October 1, 2021, the Company launched the SIP and the ESPP, through which employees can purchase shares at a discounted price. At the end of six months, shares will automatically be purchased at the lower of the opening and closing price of the shares for the saving period minus a 15% discount. 2020 Share Option Plan In September 2020, the Company’s board of directors adopted, and the Company’s shareholders approved, the 2020 Share Option and Incentive Plan, or the 2020 Plan, which became effective upon the effectiveness of the Company’s Registration Statement on Form F-1 in connection with the IPO. The 2020 Plan allows the compensation and leadership development committee to make equity-based and cash-based incentive awards to the Company’s officers, employees, directors and other key persons (including consultants). Options granted under the 2020 Plan generally expire 10 years from the date of grant and typically vest over a 4 year service period with 25% of the options vesting on the first anniversary of the commencement date and the balance vesting monthly over the remaining years. The Company initially reserved 2,074,325 of its ordinary shares for the issuance of awards under the 2020 Plan. The 2020 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2022, by up to 4% of the outstanding number of ordinary shares on the immediately preceding December 31, or such lesser number of shares as determined by our compensation and leadership development committee. This number is subject to adjustment in the event of a sub-division, consolidation, share dividend or other change in our capitalization. The total number of ordinary shares that may be issued under the 2020 Plan is 3,755,119 shares as of December 31, 2023 , of which 183,933 shares remained available for future grant. The options granted in 2023 under the 2020 Plan to employees generally expire 10 years from the date of grant. There are three potential vesting terms for the 2023 grants including: (i) 25% per year over four year service period, (ii) four year service period with 25% of the vesting on the first anniversary of the commencement date and the balance vesting monthly over the remaining years; and (iii) monthly vesting over four year service period. During the years ended December 31, 2023, 2022 and 2021 , the Company granted options to purchase 2,560,916, 2,120,783 and 1,043,702 ordinary shares to employees and non-employees, respectively. 2022 Inducement Option Award During 2022, the Company granted a non-qualified share option to purchase up to 600,000 ordinary shares as an inducement grant to our chief executive officer. The non-qualified share option has a 10 year term and one-fourth vested on August 1, 2023 and the remaining three-fourths will vest in equal monthly installments over the following 36 months. The non-qualified share option has other terms that mirror those of non-qualified share options granted under the Company’s 2020 Plan and the Company’s standard form of non-qualified share option agreement. Restricted Share Units A summary of the changes in the Company’s unvested restricted share units during the years ended December 31, 2023 and 2022 are as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested and Outstanding as of December 31, 2022 271,135 $ 12.23 Granted 175,750 10.85 Vested (96,177) 11.48 Forfeited (30,505) 11.26 Unvested and Outstanding as of December 31, 2023 320,203 $ 11.79 As of December 31, 2023 and 2022, there was $3.0 million and $2.6 million of unrecognized compensation cost related to unvested restricted share units, respectively, which is expected to be recognized over a weighted-average period of 2.6 years and 3.0 years, respectively. The exercise price of restricted share units is at a nominal value less than £0.01 per share. The following table summarizes the Company’s share options activity for the years ended December 31, 2023 and 2022: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2022 5,092,732 $ 13.55 8.38 $ 13,013 Granted 2,560,916 $ 10.08 Exercised (166,801) $ 0.01 Cancelled or forfeited (517,519) $ 18.85 Outstanding as of December 31, 2023 6,969,328 $ 13.14 7.73 $ 14,070 Exercisable as of December 31, 2023 3,553,227 $ 12.93 6.78 $ 12,341 Unvested as of December 31, 2023 3,416,101 $ 13.35 8.72 $ 1,729 The aggregate intrinsic value of options exercised during the years ended December 31, 2023, and 2022 was $1.4 million and $5.5 million, respectively. The aggregate intrinsic value of share options is calculated as the difference between the exercise price of the share options and the fair value of the Company’s ordinary shares for those share options that had exercise prices lower than the fair value of the Company’s ordinary shares. The weighted average grant-date fair value of share options granted was $7.70 and $10.00 per share during the years ended December 31, 2023 and 2022. As of December 31, 2023 and 2022, there was $29.7 million and $30.4 million of unrecognized compensation cost related to unvested share options, which is expected to be recognized over a weighted-average period of 2.5 years and 2.8 years, respectively. Share Option Valuation The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees and directors during the years ended December 31, 2023, 2022 and 2021 were as follows: Year Ended December 31, 2023 2022 2021 Expected option life (years) 5.70 years 5.95 years 5.73 years Expected volatility 87.33 % 80.76 % 67.36 % Risk-free interest rate 3.63 % 2.26 % 0.95 % Expected dividend yield — % — % — % Fair value of underlying ordinary shares $ 10.32 $ 14.06 $ 35.21 Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands): Year Ended December 31, 2023 2022 2021 Research and development 8,910 7,358 4,569 General and administrative 8,367 5,765 4,070 Total stock based compensation expense $ 17,277 $ 13,123 $ 8,639

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income (loss) before provision for income taxes consisted of the following (in thousands): Year Ended December 31, 2023 2022 2021 United Kingdom (120,320) (92,841) (72,397) Foreign 2,636 1,744 854 Loss before provision for income taxes (117,684) (91,097) (71,543) The provision for income taxes for the years ended December 31, 2023, 2022 and 2021 was computed at the UK statutory income tax rate. The income tax provision for the years then ended comprised (in thousands): Year Ended December 31, 2023 2022 2021 Current income tax provision United Kingdom $ — $ — $ — Foreign 1,893 1,865 744 Total current expense: $ 1,893 $ 1,865 $ 744 Deferred income tax benefit: United Kingdom — — — Foreign (1,113) (1,457) (545) Total deferred income tax benefit: $ (1,113) $ (1,457) $ (545) Total provision for income taxes $ 780 $ 408 $ 199 A reconciliation of income tax expense computed at the statutory UK corporation tax rate to income taxes as reflected in the consolidated financial statements is as follows (in thousands): Year Ended December 31, 2023 2022 Corporation tax at UK statutory rate $ (27,656) $ (17,309) $ (13,592) Permanent differences 1 14 69 UK R&D tax credit 10,720 5,423 3,747 Change in valuation allowance 20,971 15,038 29,180 State income taxes 23 10 1 Deferred tax asset true-up 187 8 80 Return to provision (2,259) 1,580 (854) Equity compensation 33 (782) (8,302) Change in UK tax rate (1,258) (3,609) (10,147) Other 18 35 17 $ 780 $ 408 $ 199 Significant components of the Company’s deferred tax assets and liabilities as of December 31, 2023, 2022 and 2021 consist of the following (in thousands): Year Ended December 31, 2023 2022 2021 Net operating loss carryforward $ 64,747 $ 44,227 $ 35,947 Reserves and accruals 564 695 169 Share-based compensation 14,159 9,332 6,232 Charitable contributions 36 33 — Total deferred tax assets 79,506 54,287 42,348 Valuation allowance $ (76,072) $ (51,909) $ (41,483) Depreciation (98) (154) (99) Total deferred tax liabilities (98) (154) (99) Net deferred tax assets $ 3,336 $ 2,224 $ 766 As of December 31, 2023, 2022 and 2021, the Company had UK net operating loss carryforwards of approximately $259.0 million, $176.9 million and $144.0 million, respectively, that can be carried forward indefinitely. Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2023, 2022 and 2021 related primarily to the increases in net operating loss and were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Valuation allowance at beginning of year $ 51,909 $ 41,483 $ 13,000 Increases recorded to income tax provision 20,971 15,038 29,180 Increases recorded to CTA 3,192 — — Decreases recorded to CTA — (4,612) (697) Valuation allowance at end of year $ 76,072 $ 51,909 $ 41,483 Future realization of the tax benefits of existing temporary differences and net operating loss carryforwards ultimately depends on the existence of sufficient taxable income within the carryforward period. As of December 31, 2023, 2022 and 2021, the Company performed an evaluation to determine whether a valuation allowance was needed. The Company considered all available evidence, both positive and negative, which included the results of operations for the current and preceding years. The Company determined that it was not possible to reasonably quantify future taxable income and determined that it is more likely than not that all of the deferred tax assets will not be realized. Accordingly, the Company maintained a full valuation allowance against its net UK deferred tax assets as of December 31, 2023, 2022 and 2021. The deferred tax asset recognized relates entirely to the US entity. The Company applies the authoritative guidance on accounting for and disclosure of uncertainty in tax positions, which requires the Company to determine whether a tax position of the Company is more likely than not to be sustained upon examination, including resolution of any related appeals of litigation processes, based on the technical merits of the position. For tax positions meeting the more likely than not threshold, the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than fifty percent likelihood of being realized upon the ultimate settlement with the relevant taxing authority. There were no material uncertain tax positions as of December 31, 2023, 2022 and 2021. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense when in a taxable income position. As of December 31, 2023, 2022 and 2021, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations and comprehensive loss. The Company and its subsidiaries file corporation tax returns in the U.K. and income tax returns in the U.S. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the federal, state, or foreign tax authorities, if such tax attributes are utilized in a future period. During the second quarter of 2021, the Finance Act 2021 (the Act) was enacted in the U.K.. The Act increased the main corporation tax rate from 19% to 25% effective April 1, 2023 and enhanced the first-year capital allowance on qualifying new plant and machinery assets effective April 1, 2021. The effects on the Company’s existing deferred tax balances have been recorded and are offset by the valuation allowance maintained against the Company’s U.K. net deferred tax assets.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic and diluted net loss per share attributable to ordinary shareholders was calculated as follows (in thousands, except share and per share amounts): Year Ended December 31, 2023 2022 2021 Numerator Net loss $ (118,464) $ (91,505) $ (71,742) Net loss attributable to ordinary shareholders - basic and diluted $ (118,464) $ (91,505) $ (71,742) Denominator Weighted-average number of ordinary shares used in net loss per share - basic and diluted 51,028,024 42,436,292 39,997,587 Net loss per share - basic and diluted $ (2.32) $ (2.16) $ (1.79) The Company’s potentially dilutive securities, which include unvested ordinary shares, unvested restricted share units, options granted and warrants have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of ordinary shares outstanding used to calculate both basic and diluted net loss per share attributable to ordinary shareholders is the same. The Company excluded the following potential ordinary shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to ordinary shareholders for the years ended December 31, 2023, 2022 and 2021 because including them would have had an anti-dilutive effect: Year Ended December 31, 2023 2022 2021 Unvested restricted share units 320,203 271,135 115,140 Vested restricted share units, for which shares are not in issue — 17,888 57,875 Share options 6,969,328 5,092,732 3,915,503 Warrants 16,170,972 — — 23,460,503 5,381,755 4,088,518

Right of use of assets

Right of use of assets	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Right of use assets	Right of use assets New York, USA In August 2022, the Company entered into a twelve month membership agreement with WeWork for rentable office space. The membership was cancellable with 90 days’ notice. This membership was accounted for as a short-term lease as the Company was not reasonably certain to extend the lease beyond twelve months and was therefore not recognized on the Company’s consolidated balance sheets. On October 31, 2023, the Company terminated the membership agreement with WeWork for rentable office space in New York, NY. The Company is not required to pay any membership fees, for any period, following the termination date. In September 2023, the Company entered into a lease agreement for office space located in New York, NY, that was undergoing construction to get the space ready for use. The required improvements were subsequently completed in October 2023 and the space was made available for use, resulting in the lease commencing on October 9, 2023. The stated lease term is three years. Lease payments will be made on a monthly basis and increase approximately 3.5% each year over the lease term. The total commitment for lease payments over the stated term is $0.7 million. The lease agreement has a noncancellable lease term of 2 years due to a one-time termination option, which becomes effective following the two-year anniversary of the commencement date. If exercised, the Company would pay the landlord a termination fee equal to three months of the lease payments in effect at the time of termination. Soho, London, UK In July 2021, the Company entered into a two-year operating lease with Fora Space Limited commencing on September 1, 2021. The noncancellable term is 24 months and there was no option to extend the lease. The recurring residency fee per month is £136,200, and the Company paid a refundable deposit of £136,200 at the execution of the agreement. Additionally, at the start of each calendar year, the monthly residency fee was subject to an automatic inflation linked increase of the previous years’ amount. In April 2023, the Company entered into a two-year operating lease with Fora Space Limited commencing on September 1, 2023. The noncancellable term is 24 months and there is no option to extend the lease. The recurring residency fee per month is £130,000, and the Company paid a refundable deposit of £156,000 at the execution of the agreement. Denmark Hill, London, UK In March 2022, the Company entered into an agreement for a lease with South London and Maudsley NHS Foundation Trust for land and buildings at 5 Windsor Walk, Maudsley Hospital, Denmark Hill, London, UK. The lease commenced on June 21, 2022 and has a contractual term of five years. The rent is £180,000 per year, with no deposit payable. The following table summarizes our costs included in our consolidated statements of operations and comprehensive loss related to right of use lease assets we have entered for the years ended December 31, 2023, 2022 and 2021 (in thousands): Year Ended December 31, 2023 2022 2021 Lease cost Operating lease cost $ 2,331 $ 2,263 $ 1,844 Short-term lease cost 279 256 86 $ 2,610 $ 2,519 $ 1,930 Other information: Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 2,264 $ 2,219 $ 1,971 Right-of-use assets obtained in exchange for new operating lease liabilities 4,184 783 4,513 Weighted average remaining lease term (in years) 1.96 1.58 1.64 Weighted average discount rate 8.49% 5.70% 4.99% The following table summarizes the future minimum lease payments due under operating leases as of December 31, 2023, (in thousands): December 31, 2024 2,506 December 31, 2025 1,822 December 31, 2026 229 December 31, 2027 95 Total future minimum lease payments $ 4,652 Less: imputed interest (359) Total $ 4,293

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings From time to time, the Company may be a party to litigation or subject to claims incident to the ordinary course of business. The Company was not a party to any material litigation and did not have material contingency reserves established for any liabilities as of December 31, 2023, 2022 or 2021. Indemnification In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. In accordance with its Articles of Association, the Company has indemnification obligations to its officers and directors for certain events or occurrences, subject to certain limits, while they are serving at the Company’s request in such capacity. There have been no claims to date, and the Company has director and officer insurance that may enable it to recover a portion of any amounts paid for future potential claims.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events During the first quarter quarter of 2024, through February 23, 2024, under our Sales Agreement with Cowen and Company, LLC, or Cowen, under which the Company may issue and sell its ADSs, each representing one ordinary share, we sold 2,154,798 ADSs, resulting in $22.4 million in net proceeds. On February 27, 2024, we received warrant exercise notices from an investor that participated in our August 2023 PIPE indicating its intention to exercise warrants for 901,050 ADSs. On February 28, 2024, we received the full exercise proceeds of $8.9 million for the notice to exercise warrants. The exercise of the warrants has not settled and the underlying ADSs have not yet been issued. The ADSs issuable upon exercise of these warrants are registered for resale pursuant to a resale registration statement on Form S-3 (File No. 333-274436) which was declared by the Securities and Exchange Commission (SEC) on September 18, 2023.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net loss	$ (118,464)	$ (91,505)	$ (71,742)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation
Principles of Consolidation	Principles of 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 reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of income and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, research and development expenses and the research and development tax credit. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments that have maturities of three months or less when acquired to be cash equivalents. The Company does not currently have any material cash equivalents.
Restricted Cash	Restricted Cash
Investment	Investment
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under U.S. GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the inputs for the first two are considered observable and the inputs for the last are considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques The carrying amounts reflected in the consolidated balance sheets for the Company’s cash and cash equivalents, restricted cash, accounts payable and accrued expenses approximate fair value because of the short-term nature of these instruments.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that subject the Company to credit risk consist primarily of cash and cash equivalents. The Company places cash and cash equivalents in diversified and established financial institutions. Accounts at each institution are insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000. The Company has cash and cash equivalents in excess of the FDIC insured limit. The Company has no significant off-balance-sheet risk or concentration of credit risk, such as foreign exchange contracts, options contracts, or other foreign hedging arrangements.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Estimated Useful Life Lab equipment 5 years Office equipment 3-5 years Furniture and fixtures 3 years Leasehold improvements Shorter of useful life or remaining lease term
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses or had triggering events related to its underlying assets for the years ended December 31, 2023 and 2022.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage its business as a single operating segment, which carries out its operations in two geographic regions: the United Kingdom, or UK, and the United States. The Company’s property and equipment are primarily located in the UK. The Company’s singular concentration is focused on accelerating patient access to evidence-based innovation in mental health.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, share-based compensation and benefits, travel, and external costs of outside vendors engaged to conduct clinical development activities, clinical trials and the cost to manufacture clinical trial materials.
Research Contract Costs, Prepayments and Accruals	Research Contract Costs, Prepayments and Accruals The Company has entered into various research and development-related contracts with research institutions and other companies. These agreements are generally cancellable, and related payments are recorded as research and development expenses as incurred. The Company records prepayments and accruals for estimated ongoing research costs and receives updated estimates of costs and amounts owed on a monthly basis from its third-party service providers. When evaluating the adequacy of the prepayments and accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted cost estimates from third-party service providers. Estimates are made in determining the prepaid and accrued balances at the end of any reporting period. The Company considers any prepayment that is more than 12 months in advance of the associated expense to be long-term. Actual results could differ from the Company’s estimates. The Company’s historical prepayments and accrual estimates have not been materially different from the actual costs.
Share-Based Compensation	Share-Based Compensation The Company accounts for all share-based payment awards granted to employees and non-employees as share-based compensation expense at fair value. The Company grants equity awards under its share-based compensation programs, which may include share options and restricted share units. The measurement date for employee and non-employee awards is the date of grant, and share-based compensation costs are recognized as an expense over the requisite service period, which is the vesting period, on a straight-line basis. Share-based compensation expense is classified in the accompanying consolidated statements of operations and comprehensive loss based on the function to which the related services are provided. The Company recognizes share-based compensation expense for the portion of awards that have vested. Forfeitures are recorded as they occur. On October 1, 2021, the Company launched the Share Incentive Plan, or the SIP, and Employee Share Purchase Plan, or the ESPP, through which employees can purchase shares at a discounted price. The Company estimates the fair value of stock options and shares to be issued under the SIP and ESPP using the Black-Scholes option-pricing model on the date of grant. The fair value of shares to be issued under these plans are recognized and amortized on a straight-line basis over the purchase period, which is generally six months. There have been no performance conditions attached to the share options granted by the Company to date. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 8 for the Company’s assumptions used in connection with option grants made during the periods covered by these consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility . The Company lacks sufficient company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The Company utilizes this method due to the lack of historical exercise data and the plain nature of its share-based awards. Risk-free interest rate . The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. In addition, the Loan Agreement with Hercules currently prohibits dividends that may be declared or paid on our ordinary shares. Fair value of ordinary shares. The fair value of ordinary shares is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the day prior to or day of the grant.
Leases	Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and current and non-current lease liabilities, as applicable. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets and to allocate all the contract consideration to the lease component only. All the Company’s leases are classified as operating leases. Lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. When readily determinable, the discount rate used to calculate the lease liability is the rate implicit in the lease. As the Company’s leases do not typically provide an implicit rate, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. As the Company does not have a rating agency-based credit rating, quotes were obtained from lenders to establish an estimated secured rate to borrow based on Company and market-based factors as of the respective lease measurement dates. The Company has elected not to recognize leases with an original term of one year or less on the balance sheets. The Company typically only includes the non-cancelable lease term in its assessment of a lease arrangement unless there is an option to extend the lease that is reasonably certain of exercise. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date. Operating lease costs are recognized on a straight-line basis over the lease term, and they are categorized within research and development and general and administrative expenses in the consolidated statements of operations and comprehensive loss. The operating lease cash flows are categorized under net cash used in operating activities in the consolidated statements of cash flows.
Foreign Currency Translation	Foreign Currency Translation The functional currency is the currency of the primary economic environment in which an entity’s operations are conducted. On January 1, 2023, Compass Pathways plc and its wholly owned subsidiary Compass Pathfinder Holdings Limited changed their functional currency to the U.S. dollar. Compass Pathways plc and Compass Pathfinder Holdings Limited have no operating activities and their primary functions are to serve as a financing vehicle to fund the operations of the Company’s operating entities, to serve as the listing company needed to access U.S. capital markets, and to hold investments. Therefore, its financing source is the primary indicator of its cash flows and its functional currency. The change in functional currency from the British Pound Sterling is due to a change in the source of the Company’s financing and cash flows going forward, which will now primarily be U.S. Dollars (“USD”). The functional currency of Compass Pathfinder Holdings Limited’s wholly owned non-U.S. subsidiary, Compass Pathfinder Limited, is British Pound Sterling and the functional currency of its U.S. subsidiary, Compass Pathways Inc. is USD. The functional currency of these subsidiaries is the same as the local currency. The translated balances of monetary and non-monetary assets and liabilities recorded in the reporting entity’s consolidated financial statements as of the end of the prior reporting period become the new accounting basis for those assets and liabilities in the period of the change. To the extent that the distinct and separable operation has monetary assets and liabilities denominated in the old functional currency, such balances will create transaction gains and losses subsequent to the change in functional currency. The balance recorded in the cumulative translation adjustment account for prior periods is not reversed upon the change in functional currency. The Company translates the assets and liabilities of Compass Pathfinder Limited into USD at the exchange rate in effect on the balance sheet date. Income and expenses are translated at the average exchange rate in effect during the period. Unrealized translation gains and losses are recorded as a cumulative translation adjustment, which is included in the consolidated statements of shareholders’ equity as a component of accumulated other comprehensive income/(loss).
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in its tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that deferred tax assets will be recovered in the future to the extent management believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more- likely-than-not to be sustained, the tax position is then assessed as the amount of benefit to recognize in the consolidated financial statements. The amount of benefit that may be used is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate, as well as the related net interest and penalties. As of December 31, 2023 and 2022, the Company has not identified any material uncertain tax positions. The Company recognizes interest and penalties related to unrecognized tax benefits on the income tax expense line in the accompanying consolidated statements of operations and comprehensive loss. As of December 31, 2023 and 2022 no accrued interest or penalties are included on the related tax liability line in the consolidated balance sheets.
Benefit from Research and Development Tax Credit	Benefit from Research and Development Tax Credit As a company that carries out extensive research and development activities, the Company benefits from the UK research and development tax credit regime under the scheme for small or medium-sized enterprises, or SME. Under the SME regime, in effect through December 31, 2023, the Company is able to surrender some of its trading losses that arise from qualifying research and development activities for a cash rebate of a portion of such qualifying research and development expenditure. Up until April 1, 2023 the effective rate was 33.3% on in-house expenditures and 21.7% on work that was contracted out (to unconnected subcontractors). On and after April 1, 2023, the effective rates reduced to 18.6% and 12.1%, respectively. New rules were announced in the Finance Bill 2023-24 for an enhanced effective rate of relief for loss making research intensive SMEs, which would be 27.0% for qualifying in-house expenditures and 17.5% for qualifying subcontracted expenditures. The legislation was not substantively enacted at the balance sheet date, although based on the proposed rules, the Company does not believe that it would meet the criteria for the enhanced rate of relief for the year through December 31, 2023. After the Finance Bill has received Royal Assent, the R&D claim will be reviewed at a transaction level, and the threshold calculation prepared with more certainty to determine whether the enhanced rate can be applied for submission of the claim. The Company currently meets the conditions of the SME regime. A large portion of costs relating to research and development, clinical trials and manufacturing activities are eligible for inclusion within these tax credit cash rebate claims. The Company is subject to corporate taxation in the UK. Due to the nature of the business, the Company has generated losses since inception. The benefit from research and development, or R&D, tax credits is recognized in the consolidated statements of operations and comprehensive loss as a component of other income, net, and represents the sum of the research and development tax credits recoverable in the UK. The UK research and development tax credit is fully refundable to the Company and is not dependent on current or future taxable income. As a result, the Company has recorded the entire benefit from the UK research and development tax credit as a benefit which is included in net loss before income tax and accordingly, not reflected as part of the income tax provision. If, in the future, any UK research and development tax credits generated are needed to offset a corporation tax liability in the UK, that portion would be recorded as a benefit within the income tax provision and any refundable portion not dependent on taxable income would continue to be recorded within other income, net. The Company may not be able to continue to claim research and development tax credits under the SME regime in the future because it may no longer qualify as a small or medium-sized company. In addition, there is a maximum cap in respect of a given project of €7.5 million which may impact the Company’s ability to claim R&D tax credits in future. Further, the U.K. Finance Act of 2021 introduced a cap on credit claims under the SME Program in excess of £20,000 with effect from April 2021 by reference to, broadly, three times the total Pay As You Earn, or PAYE, and National Insurance Contributions, or NICs, liability of the company, subject to an exception which prevents the cap from applying. That exception requires the company to be creating, taking steps to create or managing intellectual property, as well as having qualifying research and development expenditure in respect of connected parties, which does not exceed 15% of the total claimed. If such exception does not apply, this could restrict the amount of payable credit that the Company claims. Unsurrendered UK losses may be carried forward indefinitely to be offset against future taxable profits, subject to numerous utilization criteria and restrictions. The amount that can be offset each year is limited to £5.0 million plus an incremental 50% of UK taxable profits.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in shareholders’ equity that result from transactions and economic events other than those with shareholders. For the years ended December 31, 2023 and 2022, the only component of accumulated other comprehensive loss is foreign currency translation adjustment.
Net Loss per Share	Net Loss per Share The Company has reported losses since inception and has computed basic net loss per share attributable to ordinary shareholders by dividing net loss attributable to ordinary shareholders by the weighted-average number of ordinary shares outstanding for the period, without consideration for potentially dilutive securities. The Company computes diluted net loss per ordinary share after giving consideration to all potentially dilutive ordinary shares, including unvested restricted shares, outstanding options and warrants. Because the Company has reported net losses since inception, these potential ordinary shares have been anti-dilutive and basic and diluted loss per share were the same for all periods presented.
Derivatives	Derivatives
Long-term Debt	Long-term Debt On June 30, 2023, the Company entered into the Loan Agreement with Hercules. The Company assessed all terms and features of the Loan Agreement in order to identify any potential embedded features that would require bifurcation. As part of this analysis, the Company assessed the economic characteristics and risks of the debt. The Company determined that all features of the Loan Agreement are clearly and closely associated with a debt host and, as such, do not require separate accounting as a derivative liability. Debt issuance costs consist of costs incurred in obtaining long-term financing. These costs are classified on the consolidated balance sheet as a direct deduction from the carrying amount of the related debt liability. These expenses are deferred and amortized as part of interest expense in the consolidated statement of operations using the effective interest rate method over the term of the debt agreement.
Warrants	Warrants On June 30, 2023, the Company entered into a warrant agreement with Hercules. The Company assessed all terms and features of the Warrant Agreement in order to determine accounting classification of the warrants as equity or liability. As part of this analysis, the Company determined it appropriate to account for the warrants issued under the Loan Agreement as equity. On August 18, 2023, in connection with the PIPE, the Company issued and sold PIPE Warrants to purchase up to 16,076,750 ADSs, each representing one ordinary share, at an exercise price of $9.93 per ADS. The PIPE Warrants are exercisable for a three year period beginning in February 2024. The Company assessed all terms and features of the PIPE Warrant Agreement in order to determine accounting classification of the warrants as equity or liability. As part of this analysis, the Company determined it appropriate to account for the PIPE Warrants as equity. The Company measures warrants at inception at fair value using the Black-Scholes valuation model. Assumptions used in the warrant pricing model include the following: Expected volatility . The Company lacks sufficient company-specific historical and implied volatility information for its ordinary shares. Therefore, it estimates its expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. Expected term. The expected term of the Hercules warrants is ten years. The expected term of the PIPE Warrants is three and a half years. Risk-free interest rate . The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of the issuance for time periods that are approximately equal to the expected term of the warrant. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. In addition, the Loan Agreement with Hercules currently prohibits, and any future debt financing arrangements may contain terms prohibiting or limiting the number of dividends that may be declared or paid on our ordinary shares. Fair value of ordinary shares. The fair value of the warrants is determined by reference to the closing price of ADSs on the Nasdaq Global Select Market on the day of issuance.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In November 2023, the Financial Accounting Standard Board ("FASB") issued new guidance designed to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant expenses per segment. The guidance is effective for all fiscal years beginning after December 15, 2023, and for interim periods beginning after December 15, 2024. The new standard must be adopted on a retrospective basis and early adoption is permitted. The Company is not early adopting the standard. We are currently evaluating this guidance to determine its impact on our consolidated financial statements. In December 2023, the FASB issued new guidance designed to improve income tax disclosure requirements, primarily through increased disaggregation disclosures within the effective tax rate reconciliation as well as enhanced disclosures on income taxes paid. The guidance is effective for all fiscal years beginning after December 15, 2024. The new standard can be adopted on a prospective basis with an option to be adopted retrospectively and early adoption is permitted. The Company is not early adopting the standard. We are currently evaluating this guidance to determine its impact on our consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Schedule of Property and Equipment	Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Estimated Useful Life Lab equipment 5 years Office equipment 3-5 years Furniture and fixtures 3 years Leasehold improvements Shorter of useful life or remaining lease term

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2023 2022 UK R&D tax credit $ 27,877 $ 13,972 Prepaid insurance premium 1,885 2,818 Prepaid research and development 6,826 28,211 VAT recoverable 1,052 1,652 Other current assets 1,895 1,042 $ 39,535 $ 47,695

Long-term Prepaid Expenses an_2

Long-term Prepaid Expenses and Other Assets (Tables)	12 Months Ended
	Dec. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Long-term Prepaid Expenses and Other Assets	Long-term prepaid expenses and other assets consisted of the following (in thousands): December 31, 2023 2022 Prepaid research and development - long-term 5,955 — Property and equipment 423 617 Other investment 469 469 Other assets 202 327 $ 7,049 $ 1,413

Accrued Expenses and Other Li_2

Accrued Expenses and Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Other Liabilities Disclosure [Abstract]
Schedule of Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consisted of the following (in thousands): December 31, 2023 2022 Accrued research and development expense $ 2,117 $ 1,684 Accrued professional expenses 1,077 1,284 Accrued compensation and benefit costs 7,069 5,534 Payroll tax payable 13 167 Other liabilities 1,025 656 $ 11,301 $ 9,325

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Long-term debt consisted of the following (in thousands): December 31, 2023 Term loan payable $ 30,000 End of term charge 1,425 Future principal payments and end of term charge $ 31,425 PIK interest payable 216 Unamortized debt issuance costs (2,884) Carrying value of long-term debt $ 28,757
Schedule of Maturities of Long-Term Debt	Future principal payments, including End of Term Charge, are as follows (in thousands): December 31, 2024 — December 31, 2025 6,572 December 31, 2026 14,166 December 31, 2027 10,687 Total $ 31,425

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Nonvested Restricted Share Units Activity	A summary of the changes in the Company’s unvested restricted share units during the years ended December 31, 2023 and 2022 are as follows: Number of Shares Weighted Average Grant Date Fair Value Unvested and Outstanding as of December 31, 2022 271,135 $ 12.23 Granted 175,750 10.85 Vested (96,177) 11.48 Forfeited (30,505) 11.26 Unvested and Outstanding as of December 31, 2023 320,203 $ 11.79
Schedule of Share-based Payment Arrangement, Option Activity	The following table summarizes the Company’s share options activity for the years ended December 31, 2023 and 2022: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2022 5,092,732 $ 13.55 8.38 $ 13,013 Granted 2,560,916 $ 10.08 Exercised (166,801) $ 0.01 Cancelled or forfeited (517,519) $ 18.85 Outstanding as of December 31, 2023 6,969,328 $ 13.14 7.73 $ 14,070 Exercisable as of December 31, 2023 3,553,227 $ 12.93 6.78 $ 12,341 Unvested as of December 31, 2023 3,416,101 $ 13.35 8.72 $ 1,729
Schedule of Valuation Assumptions	The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees and directors during the years ended December 31, 2023, 2022 and 2021 were as follows: Year Ended December 31, 2023 2022 2021 Expected option life (years) 5.70 years 5.95 years 5.73 years Expected volatility 87.33 % 80.76 % 67.36 % Risk-free interest rate 3.63 % 2.26 % 0.95 % Expected dividend yield — % — % — % Fair value of underlying ordinary shares $ 10.32 $ 14.06 $ 35.21
Schedule of Share-based Compensation Expense	Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands): Year Ended December 31, 2023 2022 2021 Research and development 8,910 7,358 4,569 General and administrative 8,367 5,765 4,070 Total stock based compensation expense $ 17,277 $ 13,123 $ 8,639

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	Income (loss) before provision for income taxes consisted of the following (in thousands): Year Ended December 31, 2023 2022 2021 United Kingdom (120,320) (92,841) (72,397) Foreign 2,636 1,744 854 Loss before provision for income taxes (117,684) (91,097) (71,543)
Schedule of Components of Income Tax Expense (Benefit)	The income tax provision for the years then ended comprised (in thousands): Year Ended December 31, 2023 2022 2021 Current income tax provision United Kingdom $ — $ — $ — Foreign 1,893 1,865 744 Total current expense: $ 1,893 $ 1,865 $ 744 Deferred income tax benefit: United Kingdom — — — Foreign (1,113) (1,457) (545) Total deferred income tax benefit: $ (1,113) $ (1,457) $ (545) Total provision for income taxes $ 780 $ 408 $ 199
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of income tax expense computed at the statutory UK corporation tax rate to income taxes as reflected in the consolidated financial statements is as follows (in thousands): Year Ended December 31, 2023 2022 Corporation tax at UK statutory rate $ (27,656) $ (17,309) $ (13,592) Permanent differences 1 14 69 UK R&D tax credit 10,720 5,423 3,747 Change in valuation allowance 20,971 15,038 29,180 State income taxes 23 10 1 Deferred tax asset true-up 187 8 80 Return to provision (2,259) 1,580 (854) Equity compensation 33 (782) (8,302) Change in UK tax rate (1,258) (3,609) (10,147) Other 18 35 17 $ 780 $ 408 $ 199
Schedule of Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax assets and liabilities as of December 31, 2023, 2022 and 2021 consist of the following (in thousands): Year Ended December 31, 2023 2022 2021 Net operating loss carryforward $ 64,747 $ 44,227 $ 35,947 Reserves and accruals 564 695 169 Share-based compensation 14,159 9,332 6,232 Charitable contributions 36 33 — Total deferred tax assets 79,506 54,287 42,348 Valuation allowance $ (76,072) $ (51,909) $ (41,483) Depreciation (98) (154) (99) Total deferred tax liabilities (98) (154) (99) Net deferred tax assets $ 3,336 $ 2,224 $ 766
Summary of Valuation Allowance	Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2023, 2022 and 2021 related primarily to the increases in net operating loss and were as follows (in thousands): Year Ended December 31, 2023 2022 2021 Valuation allowance at beginning of year $ 51,909 $ 41,483 $ 13,000 Increases recorded to income tax provision 20,971 15,038 29,180 Increases recorded to CTA 3,192 — — Decreases recorded to CTA — (4,612) (697) Valuation allowance at end of year $ 76,072 $ 51,909 $ 41,483

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted net loss per share attributable to ordinary shareholders was calculated as follows (in thousands, except share and per share amounts): Year Ended December 31, 2023 2022 2021 Numerator Net loss $ (118,464) $ (91,505) $ (71,742) Net loss attributable to ordinary shareholders - basic and diluted $ (118,464) $ (91,505) $ (71,742) Denominator Weighted-average number of ordinary shares used in net loss per share - basic and diluted 51,028,024 42,436,292 39,997,587 Net loss per share - basic and diluted $ (2.32) $ (2.16) $ (1.79)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The Company excluded the following potential ordinary shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to ordinary shareholders for the years ended December 31, 2023, 2022 and 2021 because including them would have had an anti-dilutive effect: Year Ended December 31, 2023 2022 2021 Unvested restricted share units 320,203 271,135 115,140 Vested restricted share units, for which shares are not in issue — 17,888 57,875 Share options 6,969,328 5,092,732 3,915,503 Warrants 16,170,972 — — 23,460,503 5,381,755 4,088,518

Right of use of assets (Tables)

Right of use of assets (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Schedule of Costs Included in Operating Expenses Related To Right of Use Assets	The following table summarizes our costs included in our consolidated statements of operations and comprehensive loss related to right of use lease assets we have entered for the years ended December 31, 2023, 2022 and 2021 (in thousands): Year Ended December 31, 2023 2022 2021 Lease cost Operating lease cost $ 2,331 $ 2,263 $ 1,844 Short-term lease cost 279 256 86 $ 2,610 $ 2,519 $ 1,930 Other information: Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows used in operating leases $ 2,264 $ 2,219 $ 1,971 Right-of-use assets obtained in exchange for new operating lease liabilities 4,184 783 4,513 Weighted average remaining lease term (in years) 1.96 1.58 1.64 Weighted average discount rate 8.49% 5.70% 4.99%
Schedule of Future Minimum Lease Payments Due Under Operating Leases	The following table summarizes the future minimum lease payments due under operating leases as of December 31, 2023, (in thousands): December 31, 2024 2,506 December 31, 2025 1,822 December 31, 2026 229 December 31, 2027 95 Total future minimum lease payments $ 4,652 Less: imputed interest (359) Total $ 4,293

Nature of Business (Details)

Nature of Business (Details) $ / shares in Units, $ in Thousands

1 Months Ended

2 Months Ended

12 Months Ended

27 Months Ended

Feb. 27, 2024 shares

Aug. 18, 2023 $ / shares shares

Aug. 16, 2023 $ / shares shares

Oct. 08, 2021 USD ($)

May 19, 2021 USD ($)

Feb. 23, 2024 USD ($) shares

Dec. 31, 2023 USD ($)

Dec. 31, 2022 USD ($)

Dec. 31, 2021 USD ($)

Dec. 31, 2023 USD ($) shares

Dec. 31, 2023 USD ($) shares

Feb. 29, 2024

Jun. 30, 2023 USD ($)

Conversion of Stock [Line Items]

Ordinary share conversion ratio

1

1

Net loss

$ 118,464

$ 91,505

$ 71,742

Accumulated deficit

379,610

261,146

$ 379,610

$ 379,610

Cash and cash equivalents

$ 220,198

$ 143,206

$ 273,243

$ 220,198

$ 220,198

Subsequent event

Conversion of Stock [Line Items]

Ordinary share conversion ratio

1

PIPE Warrants

Conversion of Stock [Line Items]

Term of warrants and rights outstanding

3 years 6 months

3 years 6 months

3 years 6 months

PIPE Warrants | Subsequent event

Conversion of Stock [Line Items]

Term of warrants and rights outstanding

3 years

Loan Agreement

Conversion of Stock [Line Items]

Convertible notes, face amount

$ 50,000

Loan Agreement, Term Loan One

Conversion of Stock [Line Items]

Convertible notes, face amount

$ 30,000

Initial Public Offering

Conversion of Stock [Line Items]

Consideration received on transaction

$ 154,800

At-The-Market Offering

Conversion of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares) | shares

2,982,038

2,982,038

Consideration received on transaction

$ 28,600

$ 28,600

At-The-Market Offering | Subsequent event

Conversion of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares) | shares

2,154,798

Consideration received on transaction

$ 22,400

Private Placement

Conversion of Stock [Line Items]

Ordinary share conversion ratio

1

Sale of stock, shares issued in transaction (in shares) | shares

16,076,750

16,076,750

Sale of stock, price per share (in dollars per share) | $ / shares

$ 7.78

Purchase price (in dollars per share) | $ / shares

$ 9.93

$ 9.93

Private Placement | Subsequent event

Conversion of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares) | shares

901,050

Private Placement | PIPE Warrants | Subsequent event

Conversion of Stock [Line Items]

Term of warrants and rights outstanding

3 years

American Depositary Shares | Initial Public Offering

Conversion of Stock [Line Items]

Maximum amount of stock that may be sold

$ 150,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Property, Plant and Equipment (Details)	Dec. 31, 2023
Lab equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Office equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Office equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	Useful Life, Shorter of Lease Term or Asset Utility [Member]

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Narrative (Details) $ / shares in Units, £ in Thousands, € in Millions					2 Months Ended	12 Months Ended
	Feb. 27, 2024 shares	Aug. 18, 2023 $ / shares shares	Aug. 16, 2023 $ / shares shares	Oct. 08, 2021	Feb. 23, 2024	Dec. 31, 2023 EUR (€) region	Dec. 31, 2023 GBP (£) region	Dec. 31, 2022 USD ($)	Dec. 31, 2021	Feb. 29, 2024	Dec. 31, 2023 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity security without readily determinable fair value											$ 500,000
Impairment loss											$ 0
Number of geographic regions | region						2	2
Expected dividend yield (in percent)						0%	0%	0%	0%
Maximum qualifying research and development expenditures with connected parties, percent						15%	15%
Gain on sale of derivatives								$ 2,300,000
Ordinary share conversion ratio		1		1
Delix Therapeutics, Inc.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ownership percentage in Delix Therapeutics, Inc											8%
Subsequent event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ordinary share conversion ratio					1
Measurement Input, Expected Dividend Rate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Measurement input, warrants and rights											0
PIPE Warrants
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Term of warrants and rights outstanding											3 years 6 months
PIPE Warrants | Subsequent event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Term of warrants and rights outstanding										3 years
Hercules Warrants
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Term of warrants and rights outstanding											10 years
Private Placement
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sale of stock, shares issued in transaction (in shares) | shares		16,076,750	16,076,750
Ordinary share conversion ratio			1
Purchase price (in dollars per share) | $ / shares		$ 9.93	$ 9.93
Private Placement | Subsequent event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sale of stock, shares issued in transaction (in shares) | shares	901,050
Private Placement | PIPE Warrants | Subsequent event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Term of warrants and rights outstanding										3 years
United Kingdom Research and Development Tax Credit Regime, Small or Medium-Sized Enterprises (SME)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total aid claimable (in Euros) | €						€ 7.5
Cap on payable claims (in GBP) | £							£ 20
United Kingdom Research and Development Tax Credit Regime
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Annual offset amount (in GBP) | £							£ 5,000
Percentage of taxable profits (in percent)						50%	50%

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
UK R&D tax credit	$ 27,877	$ 13,972
Prepaid insurance premium	1,885	2,818
Prepaid research and development	6,826	28,211
VAT recoverable	1,052	1,652
Other current assets	1,895	1,042
Prepaid expenses and other current assets	$ 39,535	$ 47,695

Long-term Prepaid Expenses an_3

Long-term Prepaid Expenses and Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research and development - long-term	$ 5,955	$ 0
Property and equipment	423	617
Other investment	469	469
Other assets	202	327
Long-term prepaid expenses and other assets	$ 7,049	$ 1,413

Accrued Expenses and Other Li_3

Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Other Liabilities Disclosure [Abstract]
Accrued research and development expense	$ 2,117	$ 1,684
Accrued professional expenses	1,077	1,284
Accrued compensation and benefit costs	7,069	5,534
Payroll tax payable	13	167
Other liabilities	1,025	656
Total accrued expenses and other liabilities	$ 11,301	$ 9,325

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
	Jun. 30, 2023	Dec. 31, 2023
Debt Instrument [Line Items]
Debt issuance costs		$ 3.3
Number of shares available for purchase, percent of principal amount of term loan (as a percent)		0.025
Number of options exercisable (in shares)		94,222
Fair value of exercisable options		$ 0.7
Debt interest expense		2.2
Facility Fees
Debt Instrument [Line Items]
Debt issuance costs		0.4
Company Fees
Debt Instrument [Line Items]
Debt issuance costs		0.8
Warrants
Debt Instrument [Line Items]
Debt issuance costs		0.7
End of Term Charge
Debt Instrument [Line Items]
Debt issuance costs		$ 1.4
Loan Agreement
Debt Instrument [Line Items]
Convertible notes, face amount	$ 50
Stated interest rate	9.75%
Paid-in-kind interest rate	0.0140
Effective interest rate		15.80%
Market capitalization		$ 750
Loan Agreement | Prime Rate
Debt Instrument [Line Items]
Interest rate, prime margin (as a percent)	1.50%
Loan Agreement, Term Loan One
Debt Instrument [Line Items]
Convertible notes, face amount	$ 30
Loan Agreement, Term Loan Two
Debt Instrument [Line Items]
Convertible notes, face amount	10
Loan Agreement, Term Loan Three
Debt Instrument [Line Items]
Convertible notes, face amount	$ 10
Debt instrument covenant, cash on hand		$ 22.5

Debt - Components of Debt (Deta

Debt - Components of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Term loan payable	$ 30,000
End of term charge	1,425
Future principal payments and end of term charge	31,425
PIK interest payable	216
Unamortized debt issuance costs	(2,884)
Carrying value of long-term debt	$ 28,757	$ 0

Debt - Schedule of Principal Pa

Debt - Schedule of Principal Payments (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
December 31, 2024	$ 0
December 31, 2025	6,572
December 31, 2026	14,166
December 31, 2027	10,687
Future principal payments and end of term charge	$ 31,425

Shareholders' Equity (Details)

Shareholders' Equity (Details)

1 Months Ended

2 Months Ended

12 Months Ended

27 Months Ended

Feb. 27, 2024 shares

Aug. 18, 2023 $ / shares shares

Aug. 16, 2023 $ / shares shares

Oct. 08, 2021 USD ($)

May 19, 2021 shares

May 04, 2021 shares

May 19, 2021 USD ($)

Feb. 23, 2024 USD ($) shares

Dec. 31, 2023 USD ($) vote shares

Dec. 31, 2022 £ / shares shares

Dec. 31, 2021 £ / shares shares

Dec. 31, 2023 USD ($) shares

Dec. 31, 2023 USD ($) shares

Feb. 29, 2024

Dec. 31, 2023 £ / shares

Dec. 31, 2023 USD ($) shares

Jun. 30, 2023 USD ($) shares

Dec. 31, 2020 £ / shares

Sep. 30, 2020 £ / shares

Aug. 31, 2020 £ / shares

Class of Stock [Line Items]

Cash dividend declared or paid | $

$ 0

Ordinary share conversion ratio

1

1

Exercise of share options (in shares)

166,801

Number of shares available for purchase, percent of principal amount of term loan (as a percent)

0.025

Number of options exercisable (in shares)

94,222

Fair value of exercisable options | $

$ 700,000

Subsequent event

Class of Stock [Line Items]

Ordinary share conversion ratio

1

PIPE Warrants

Class of Stock [Line Items]

Term of warrants and rights outstanding

3 years 6 months

PIPE Warrants | Subsequent event

Class of Stock [Line Items]

Term of warrants and rights outstanding

3 years

Hercules Capital, Inc.

Class of Stock [Line Items]

Number of shares available for purchase, percent of principal amount of term loan (as a percent)

0.025

Term of warrants and rights outstanding

10 years

Number of options exercisable (in shares)

94,222

Fair value of exercisable options | $

$ 700,000

Employee Stock Purchase Plan

Class of Stock [Line Items]

Shares issued under employee share purchase plans (in shares)

52,482

22,160

0

Initial Public Offering

Class of Stock [Line Items]

Consideration received on transaction | $

$ 154,800,000

At-The-Market Offering

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

2,982,038

2,982,038

Consideration received on transaction | $

$ 28,600,000

$ 28,600,000

At-The-Market Offering | Subsequent event

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

2,154,798

Consideration received on transaction | $

$ 22,400,000

Private Placement

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

16,076,750

16,076,750

Ordinary share conversion ratio

1

Purchase price (in dollars per share) | $ / shares

$ 9.93

$ 9.93

Private Placement | Subsequent event

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

901,050

Private Placement | PIPE Warrants | Subsequent event

Class of Stock [Line Items]

Term of warrants and rights outstanding

3 years

Ordinary shares

Class of Stock [Line Items]

Sale of stock, shares issued in transaction (in shares)

600,000

4,000,000

Number of votes | vote

1

Exercise of share options (in shares)

166,801

462,722

1,476,936

Vested (in shares)

96,177

42,635

70,482

Issuance of ordinary shares to settle vested restricted stock units (in shares)

69,120

24,747

12,607

Shares settled during period (in shares)

27,057

8,986

Restricted share units vested (in shares)

78,022

Vested (in shares)

8,902

57,875

Common stock, par value (in GBP per share) | £ / shares

£ 0.008

£ 0.008

£ 0.008

£ 0.008

£ 0.008

£ 0.001

Ordinary shares | 2021 And 2022

Class of Stock [Line Items]

Issuance of ordinary shares to settle vested restricted stock units (in shares)

82,622

American Depositary Shares | Initial Public Offering

Class of Stock [Line Items]

Amount of stock authorized | $

$ 150,000,000

DEFERRED SHARES

Class of Stock [Line Items]

Common stock, par value (in GBP per share) | £ / shares

£ 21,921.504

£ 21,921.504

£ 21,921.504

£ 21,921.504

£ 21,921.504

Share-Based Compensation - 2017

Share-Based Compensation - 2017 Equity Incentive Plan (Details) - 2017 Equity Incentive Plan	12 Months Ended
	Dec. 31, 2023 day shares
Vested restricted share units, for which shares are not in issue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Number of shares authorized (in shares) | shares	1,437,252
Vested restricted share units, for which shares are not in issue | Options Granted Before June 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage (in percent)	33.30%
Vested restricted share units, for which shares are not in issue | Grant Date June 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Award vesting percentage (in percent)	25%
Vested restricted share units, for which shares are not in issue | Share-based Payment Arrangement, Tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage (in percent)	25%
Vested restricted share units, for which shares are not in issue | Share-based Payment Arrangement, Tranche two | Grant Date June 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Award vesting percentage (in percent)	75%
Vested restricted share units, for which shares are not in issue | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Vested restricted share units, for which shares are not in issue | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Award vesting percentage (in percent)	25%
Restricted Stock Units (RSUs) | Share-based Payment Arrangement, Tranche one | Grant Date June 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage (in percent)	25%
Expiration period	1 year
Percentage amount closing price is higher than listing price	20%
Threshold consecutive trading days | day	5

Share-Based Compensation - 2020

Share-Based Compensation - 2020 Employee Share Purchase Plan (Details) - Employee Stock Purchase Plan - shares		12 Months Ended
	Oct. 01, 2021	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)		340,053
Allowable increase in shares authorized for issuance, percentage of outstanding stock (in percent)		1%
Maximum increase in shares available for issuance (in shares)		510,080
Stock plan, offering period	6 months
Saving period (in percent)	15%

Share-Based Compensation - 20_2

Share-Based Compensation - 2020 Share Option Plan (Details) - shares	1 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)		2,560,916
2020 Share Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years	10 years
Award vesting period	4 years
Award vesting percentage (in percent)	25%
Shares issued (in shares)		3,755,119
2020 Share Option Plan | Vesting condition one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
Award vesting percentage (in percent)		25%
2020 Share Option Plan | Vesting condition two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
Award vesting percentage (in percent)		25%
2020 Share Option Plan | Vesting condition three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
Ordinary shares | 2020 Share Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)	2,074,325
Maximum percentage of shares outstanding number of shares reserved for issuance may increase (in percent)	4%
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)		175,750
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)		183,933
Granted (in shares)		2,560,916	2,120,783	1,043,702

Share-Based Compensation - 2022

Share-Based Compensation - 2022 Inducement Grant Option Award (Details) - 2022 Inducement Grant Option Award - Ordinary shares - shares	Aug. 01, 2022	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)		600,000
Expiration period	10 years
Award vesting period	36 months

Share-Based Compensation - Rest

Share-Based Compensation - Restricted Share Units (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) £ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Number of Shares
Granted (in shares) | shares	2,560,916	2,560,916
Unvested and Outstanding, ending balance (in shares) | shares	3,416,101	3,416,101
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	$ 7.70		$ 10
Weighted Average Grant Date Fair Value, ending balance (in dollars per share) | $ / shares	$ 13.35
Restricted Stock Units (RSUs)
Number of Shares
Unvested and Outstanding, beginning balance (in shares) | shares	271,135	271,135
Granted (in shares) | shares	175,750	175,750
Vested (in shares) | shares	(96,177)	(96,177)
Forfeited (in shares) | shares	(30,505)	(30,505)
Unvested and Outstanding, ending balance (in shares) | shares	320,203	320,203	271,135
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, beginning balance (in dollars per share) | $ / shares	$ 12.23
Weighted Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	10.85
Weighted Average Grant Date Fair Value, Vested (in dollars per share) | $ / shares	11.48
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share) | $ / shares	11.26
Weighted Average Grant Date Fair Value, ending balance (in dollars per share) | $ / shares	$ 11.79		$ 12.23
Unrecognized compensation cost | $	$ 3,000,000	$ 3,000,000	$ 2,600,000
Period for recognition (in years)	2 years 7 months 6 days	2 years 7 months 6 days	3 years
Exercise price (in pound sterling per share) | £ / shares		$ 0.01

Share-based Compensation - Shar

Share-based Compensation - Share Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Number of Shares
Granted (in shares)	2,560,916
Exercised (in shares)	(166,801)
Cancelled or forfeited (in shares)	(517,519)
Outstanding, ending balance (in shares)	6,969,328
Exercisable (in shares)	3,553,227
Unvested (in shares)	3,416,101
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 13.55
Granted (in dollars per share)	10.08
Exercised (in dollars per share)	0.01
Forfeited (in dollars per share)	18.85
Outstanding, ending balance (in dollars per share)	13.14	$ 13.55
Exercisable (in dollars per share)	12.93
Unvested (in dollars per share)	$ 13.35
Weighted Average Remaining Contractual Term (Years) and Aggregate Intrinsic Value
Outstanding balance (in years)	7 years 8 months 23 days	8 years 4 months 17 days
Exercisable (in years)	6 years 9 months 10 days
Unvested (in years)	8 years 8 months 19 days
Outstanding, aggregate intrinsic value	$ 14,070	$ 13,013
Exercisable, aggregate intrinsic value	12,341
Unvested, aggregate intrinsic value	1,729
Aggregate intrinsic value of options exercised during the period	$ 1,400	$ 5,500
Weighted Average Grant Date Fair Value, Granted (in dollars per share)	$ 7.70	$ 10
Unrecognized compensation cost of options	$ 29,700	$ 30,400
Ordinary shares
Number of Shares
Exercised (in shares)	(166,801)	(462,722)	(1,476,936)
Employee Stock Option
Weighted Average Remaining Contractual Term (Years) and Aggregate Intrinsic Value
Period for recognition (in years)	2 years 6 months	2 years 9 months 18 days
Employee Stock Option | Ordinary shares
Number of Shares
Outstanding, beginning balance (in shares)	5,092,732
Outstanding, ending balance (in shares)		5,092,732

Share-Based Compensation - Sche

Share-Based Compensation - Schedule of Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Payment Arrangement [Abstract]
Expected option life (years)	5 years 8 months 12 days	5 years 11 months 12 days	5 years 8 months 23 days
Expected volatility (in percent)	87.33%	80.76%	67.36%
Risk-free interest rate	3.63%	2.26%	0.95%
Expected dividend yield (in percent)	0%	0%	0%
Fair value of underlying ordinary shares	$ 10.32	$ 14.06	$ 35.21

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 17,277	$ 13,123	$ 8,639
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	8,910	7,358	4,569
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 8,367	$ 5,765	$ 4,070

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Tax Income (Loss) Before Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
United Kingdom	$ (120,320)	$ (92,841)	$ (72,397)
Foreign	2,636	1,744	854
Loss before income taxes	$ (117,684)	$ (91,097)	$ (71,543)

Income Taxes - Schedule of Co_2

Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current income tax provision
United Kingdom	$ 0	$ 0	$ 0
Foreign	1,893	1,865	744
Total current expense:	1,893	1,865	744
Deferred income tax benefit:
United Kingdom	0	0	0
Foreign	(1,113)	(1,457)	(545)
Total deferred income tax benefit:	(1,113)	(1,457)	(545)
Total provision for income taxes	$ 780	$ 408	$ 199

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Expense Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Corporation tax at UK statutory rate	$ (27,656)	$ (17,309)	$ (13,592)
Permanent differences	1	14	69
UK R&D tax credit	10,720	5,423	3,747
Change in valuation allowance	20,971	15,038	29,180
State income taxes	23	10	1
Deferred tax asset true-up	187	8	80
Return to provision	(2,259)	1,580	(854)
Equity compensation	33	(782)	(8,302)
Change in UK tax rate	(1,258)	(3,609)	(10,147)
Other	18	35	17
Total provision for income taxes	$ 780	$ 408	$ 199

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Net operating loss carryforward	$ 64,747	$ 44,227	$ 35,947
Reserves and accruals	564	695	169
Share-based compensation	14,159	9,332	6,232
Charitable contributions	36	33	0
Total deferred tax assets	79,506	54,287	42,348
Valuation allowance	(76,072)	(51,909)	(41,483)	$ (13,000)
Depreciation	(98)	(154)	(99)
Total deferred tax liabilities	(98)	(154)	(99)
Net deferred tax assets	$ 3,336	$ 2,224	$ 766

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 259,000,000	$ 176,900,000	$ 144,000,000
Accrued interest and penalties related to unrecognized tax benefits	0	0	0
Accrued interest or penalties related to uncertain tax positions	$ 0	$ 0	$ 0

Income Taxes - Summary of Valua

Income Taxes - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Valuation Allowance [Roll Forward]
Valuation allowance at beginning of year	$ 51,909	$ 41,483	$ 13,000
Valuation allowance at end of year	76,072	51,909	41,483
Increases recorded to income tax provision
Valuation Allowance [Roll Forward]
Valuation allowance, increase (decrease), amount	20,971	15,038	29,180
Increases recorded to CTA
Valuation Allowance [Roll Forward]
Valuation allowance, increase (decrease), amount	3,192	0	0
Decreases recorded to CTA
Valuation Allowance [Roll Forward]
Valuation allowance, increase (decrease), amount	$ 0	$ (4,612)	$ (697)

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (118,464)	$ (91,505)	$ (71,742)
Net loss attributable to ordinary shareholders - basic	(118,464)	(91,505)	(71,742)
Net loss attributable to ordinary shareholders - diluted	$ (118,464)	$ (91,505)	$ (71,742)
Weighted average ordinary shares outstanding - basic (in shares)	51,028,024	42,436,292	39,997,587
Weighted average ordinary shares outstanding - diluted (in shares)	51,028,024	42,436,292	39,997,587
Net loss per share - basic (in dollars per share)	$ (2.32)	$ (2.16)	$ (1.79)
Net loss per share - diluted (in dollars per share)	$ (2.32)	$ (2.16)	$ (1.79)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	23,460,503	5,381,755	4,088,518
Unvested restricted share units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	320,203	271,135	115,140
Vested Restricted Share Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	17,888	57,875
Share options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	6,969,328	5,092,732	3,915,503
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	16,170,972	0	0

Right of use of assets - Narrat

Right of use of assets - Narrative (Details) $ in Thousands		1 Months Ended			12 Months Ended
	Oct. 09, 2023 USD ($)	Apr. 30, 2023 GBP (£)	Aug. 31, 2022	Jul. 31, 2021	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 GBP (£)	Jun. 21, 2022
Lessee, Lease, Description [Line Items]
Lease term	3 years
Annual increase in lease payments (as a percent)	0.035
Total lease commitments | $	$ 700					$ 4,652
Operating leases, noncancelable term	2 years
Minimum lease term before option to terminate	2 years
Termination fee, monthly rent equivalent period	3 months
Deposit payable							£ 0
WeWork
Lessee, Lease, Description [Line Items]
Lease term			12 months
Lease cancellation notification period (in days)			90 days
Soho, London, UK
Lessee, Lease, Description [Line Items]
Lease term		2 years		2 years
Operating leases, noncancelable term				24 months
Operating lease, monthly payment					£ 136,200
Refundable lease deposit					136,200
Denmark Hill, London, UK
Lessee, Lease, Description [Line Items]
Lease term								5 years
Annual lease payment					£ 180,000
Second Soho London, UK Lease
Lessee, Lease, Description [Line Items]
Operating leases, noncancelable term		24 months
Operating lease, monthly payment		£ 130,000
Refundable lease deposit		£ 156,000

Right of use of assets - Summar

Right of use of assets - Summary of costs included in operating expenses related to right of use assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lease cost
Operating lease cost	$ 2,331	$ 2,263	$ 1,844
Short-term lease cost	279	256	86
Total lease cost	2,610	2,519	1,930
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows used in operating leases	2,264	2,219	1,971
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 4,184	$ 783	$ 4,513
Weighted average remaining lease term (in years)	1 year 11 months 15 days	1 year 6 months 29 days	1 year 7 months 20 days
Weighted average discount rate	8.49%	5.70%	4.99%

Right of use of assets - Summ_2

Right of use of assets - Summary of future minimum lease payments due to operating leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Oct. 09, 2023
Leases [Abstract]
December 31, 2024	$ 2,506
December 31, 2025	1,822
December 31, 2026	229
December 31, 2027	95
Total future minimum lease payments	4,652	$ 700
Less: imputed interest	359
Total	$ 4,293

Subsequent Events (Details)

Subsequent Events (Details) $ in Millions						2 Months Ended	27 Months Ended
	Feb. 28, 2024 USD ($)	Feb. 27, 2024 shares	Aug. 18, 2023 shares	Aug. 16, 2023 shares	Oct. 08, 2021	Feb. 23, 2024 USD ($) shares	Dec. 31, 2023 USD ($) shares	Dec. 31, 2023 USD ($) shares
Subsequent Event [Line Items]
Ordinary share conversion ratio			1		1
At-The-Market Offering
Subsequent Event [Line Items]
Sale of stock, shares issued in transaction (in shares)							2,982,038	2,982,038
Consideration received on transaction | $							$ 28.6	$ 28.6
Private Placement
Subsequent Event [Line Items]
Ordinary share conversion ratio				1
Sale of stock, shares issued in transaction (in shares)			16,076,750	16,076,750
Subsequent event
Subsequent Event [Line Items]
Ordinary share conversion ratio						1
Proceeds from exercise of warrants | $	$ 8.9
Subsequent event | At-The-Market Offering
Subsequent Event [Line Items]
Sale of stock, shares issued in transaction (in shares)						2,154,798
Consideration received on transaction | $						$ 22.4
Subsequent event | Private Placement
Subsequent Event [Line Items]
Sale of stock, shares issued in transaction (in shares)		901,050