Summary of Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2025
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) promulgated by the Financial Accounting Standards Board (“FASB”). All intercompany accounts and transactions have been eliminated in consolidation.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking accounts, certificates of deposit, money market funds and U.S. Treasury securities. Restricted cash represents cash held to secure a letter of credit associated with the Company’s facility lease for its corporate headquarters. The Company had $0.7 million, in restricted cash as of December 31, 2025 and 2024, which was classified as Other non-current assets on the Company’s consolidated balance sheets.
Investments in Marketable Securities	Investments in Marketable Securities The Company invests its excess cash in money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt securities and commercial paper. The Company’s investment policy limits investments to money market funds, certain types of debt securities issued by the U.S. Government and its agencies, corporate notes and commercial paper, and places restrictions on the credit ratings, maturities and concentration by type and issuer. Securities with original maturities of three months or less when purchased are included in cash and cash equivalents. We consider investments with original maturities greater than three months and remaining maturities less than one year to be short-term investments, while remaining maturities greater than one year are classified as long-term investments. As of December 31, 2025, all investments in U.S. Treasury securities were classified as available-for-sale securities, which are recorded at fair value. Unrealized holding gains and losses on available-for-sale securities are reported net of related income taxes in accumulated other comprehensive income until realized. Purchase premiums and discounts are amortized to interest income over the terms of the related securities.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and investments. The Company’s cash, cash equivalents, and investments are held by financial institutions primarily in the United States and the United Kingdom. Amounts on deposit may at times exceed federally insured limits. Management believes that the financial institutions are financially sound, and accordingly, the Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Segments	Segments Operating segments are defined as components of an enterprise with separate discrete information available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. We view our operations and manage our business as one segment.
Reclassifications	Reclassifications Certain amounts in the prior period financial statements have been reclassified to conform to the presentation of the current period financial statements. These reclassifications had no effect on previously reported net loss or comprehensive loss.
Foreign Currency Translation	Foreign Currency Translation The Company’s financial statements are presented in U.S. dollars (“USD”), the reporting currency of the Company. The functional currency of Centessa Pharmaceuticals plc is USD and the functional currency of the Centessa Subsidiaries is their respective local currency. Income and expenses have been translated into USD at average monthly exchange rates prevailing during the period. Assets and liabilities have been translated at the rates of exchange on the balance sheets dates and equity accounts at their respective historical rates. The resulting translation gain and loss adjustments are recorded directly as a separate component of shareholders’ equity as other comprehensive (loss) income. Transactions denominated in a currency other than the functional currency are remeasured based upon the exchange rate at the date of remeasurement with the resulting gain or loss included in the accompanying consolidated statements of operations and comprehensive loss within Other non-operating income (expense), net.
Use of Estimates	Use of Estimates The preparation of 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 revenues and expenses during the reporting periods. Significant areas that require management’s estimates include accrued research and development expenses, the note purchase agreement, research and development tax incentives and the recoverability of the Company’s net deferred tax assets and related valuation allowances. Estimates and assumptions 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.
Property and Equipment, net	Property and Equipment, net Property and equipment are recorded at cost and are depreciated using the straight-line method over the estimated useful lives of the respective assets. Property and equipment includes computer equipment, furniture and office equipment, which have a useful life of three to seven years. The costs of maintenance and repairs are expensed as incurred. Improvements and betterment that add new functionality or extend the useful life of the asset are capitalized. Capitalized software as a service costs representing costs incurred during the application development stage are included in “Other non-current assets” and the corresponding current portion, in “Prepaid expenses and other current assets” and is amortized using the straight line method over 5 years. Costs incurred during the preliminary project stage and the post-implementation-operation stage are expensed as incurred. Hosting fees associated with the hosting as a service arrangement are expensed on a straight line basis over the term of the hosting arrangement.
Leases	Leases In accordance with ASU No. 2016-02, Leases (“ASC 842”), the Company assesses whether an arrangement is a lease, or contains a lease at the inception of the arrangement. When an arrangement contains a lease, the Company categorizes leases with contractual terms longer than twelve months as either operating or finance. Finance leases are generally those leases that allow us to substantially utilize or pay for the entire asset over its estimated life. Assets acquired under finance leases are recorded in “Property and equipment, net.” All other leases are categorized as operating leases. The Company records right-of use ("ROU") assets and lease obligations for its finance and operating leases, which are initially recognized based on the discounted future lease payments over the term of the lease. As the rate implicit in the Company's leases may not be easily determinable, the Company uses its incremental borrowing rate to calculate the present value of the sum of the lease payments. Lease terms may include options to extend or terminate the lease. The Company will include such options in determining the lease term when it is reasonably certain that the Company will exercise such options. Operating and finance lease ROU assets are recognized net of any lease prepayments and incentives. The Company elected the practical expedient to not separate lease and non-lease components and, accordingly, accounts for them as a single lease component. Operating lease expense is recognized on a straight-line basis over the lease term. Finance lease expense is recognized based on the effective-interest method over the lease term. The Company elected not to recognize ROU assets and lease obligations for any short-term leases, which are defined as leases with an initial term of 12 months or less.
Long-Lived Assets	Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated undiscounted future cash flows, then an impairment charge is recognized for the amount by which the carrying value of the asset exceeds the estimated fair value of the asset. As of December 31, 2025, the Company believes that no revision of the remaining useful lives or write-down of long-lived assets is required.
Fair Value Measurement	Fair Value Measurement Fair value is the price that could be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value determination in accordance with applicable accounting guidance requires that a number of significant judgments be made. Additionally, fair value is used on a nonrecurring basis to evaluate assets for impairment or as required for disclosure purposes by applicable accounting guidance on disclosures about fair value of financial instruments. Depending on the nature of the assets and liabilities, various valuation techniques and assumptions are used when estimating fair value. The carrying amounts of certain of the Company’s financial instruments, including cash and cash equivalents, prepaid expense and accounts payable, are shown at cost, which approximates fair value due to the short-term nature of these instruments. The Company follows the provisions of FASB ASC Topic 820, Fair Value Measurement, for financial assets and liabilities measured on a recurring basis. The guidance requires fair value measurements be classified and disclosed in one of the following three categories: Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. Level 2: Quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liabilities. Level 3: Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity).
Debt Issuance Costs	Debt Issuance Costs For debt issuances that are not accounted for under the fair value option, such as the Loan and Security Agreement, any debt issuance costs are capitalized, recorded as an offset to the Company’s debt balances and amortized as interest expense over the term of the associated debt instrument using the effective interest method. If the maturity of the debt is accelerated as a result of default or early debt repayment, the amortization would then be accelerated. Amounts paid related to debt financing activities are presented on the consolidated balance sheet as a direct deduction from the debt liability.
License and other revenue	License and other revenue The Company recognizes revenues from collaboration, license or other research or sale arrangements when or as performance obligations are satisfied. For milestone payments, the Company assesses, at contract inception, whether the milestones are considered probable of being achieved. If it is probable that a significant revenue reversal will occur, the Company will not record revenue until the uncertainty has been resolved. Milestone payments that are contingent upon regulatory approval are not considered probable until the approvals are obtained as it is outside of the control of the Company. If it is probable that significant revenue reversal will not occur, the Company will estimate the milestone payments using the most likely amount method. The Company reassesses the milestones each reporting period to determine the probability of achievement. Any potential consideration received in the form of royalty or sales-based milestones will be recorded when the customer’s subsequent sales or usages occur. For accounting treatment related to the Genmab agreement, see Note 3 - “Revenue Recognition”.
Collaborative Arrangements	Collaborative Arrangements The Company enters into collaborative arrangements to develop and commercialize intellectual property. These arrangements typically involve two (or more) parties who are active participants in the collaboration and are exposed to significant risks and rewards dependent on the commercial success of the activities. These collaborations usually involve various activities by one or more parties, including research and development, marketing and selling and distribution. Often, these collaborations require upfront, milestone and royalty or profit share payments, contingent upon the occurrence of certain future events linked to the success of the asset in development. Amounts due to collaborative partners related to development activities are generally reflected as research and development expense.
Research and Development Expenses and Accruals and Research and Development Tax Incentives	Research and Development Expenses and Accruals All research and development costs are expensed in the period incurred and consist primarily of salaries, payroll taxes, employee benefits, stock-based compensation charges for those individuals involved in research and development efforts, third-party license fees, external research and development costs incurred under agreements with contract research organizations and consultants to conduct and support the Company’s ongoing clinical trials as well as external costs of outside vendors engaged to manufacture research and development materials. The Company has entered into various research and development contracts with clinical research organizations, clinical development and manufacturing organizations and other companies. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred. Payments made in advance of performance are reflected in the accompanying balance sheets as prepaid expenses, while payments made after performance are reflected as accrued liabilities in the accompanying balance sheets. The Company records accruals for estimated costs incurred for ongoing research and development activities. When recording accruals for ongoing research and development activities, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Nonrefundable advance payments for goods and services, including fees for process development or manufacturing and distribution of clinical supplies that will be used in future research and development activities, are recognized as expense in the period that the related goods are consumed or services are performed. Milestone payments within the Company’s licensing arrangements are recognized when achievement of the milestone is deemed probable to occur. To the extent products are commercialized and future economic benefit has been established, commercial milestones that become probable are capitalized and amortized over the estimated remaining useful life of the intellectual property. Significant judgments and estimates may be made in determining the prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. Research and Development Tax Incentives The Company participates in research tax incentive programs that are granted to companies by the United Kingdom tax authorities in order to encourage them to conduct technical and scientific research. Expenditures that meet the required criteria are eligible to receive a tax credit that is reimbursed in cash, upon surrender of loss carryforwards. Estimates of the amount of the cash refund expected to be received are determined at each reporting period and recorded as reductions to research and development expenses. The Company recorded research and development tax incentives of $22.7 million and $30.9 million during the years ended December 31, 2025 and December 31, 2024, respectively. Through December 31, 2024, the Company claimed relief under the Small and Medium Enterprise (“SME”) scheme. Beginning January 1, 2025, changes to the program in the UK have aligned the tax incentives earned for SME and large entities. The merged scheme provides relief for qualifying R&D expenditure. If the company is loss-making, a cash credit can be obtained. If the company continues to meet the SME thresholds and is loss making, then a higher rate of credit may be available under the new Enhanced R&D Intensive Support (ERIS). The Company expects eligible R&D expenditures qualifying for the credit outside of the UK will be more limited as a result of these legislative changes and it expects to recognize less tax incentives in the United Kingdom.
Share-Based Compensation	Share-Based Compensation The Company measures share-based awards, including restricted shares, restricted stock units and stock options, at their grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards. The Company determines the fair value of share-based compensation awards using the market closing price of the Company’s ADSs on the date of grant. Forfeitures of stock options are recognized in the period the forfeiture occurs. The Company classifies stock-based compensation expense in its consolidated financial statement of operations in the same manner in which the award recipient’s salary or service payments are classified. The fair value of each stock option awards is estimated on the date of grant using the Black-Scholes option pricing model, which requires inputs of subjective assumptions, including: (i) the expected volatility of the Company’s stock; (ii) the expected term of the award; (iii) the risk-free interest rate; and (iv) expected dividends. Due to the lack of Company-specific historical and implied volatility data, the Company determines the volatility for awards granted based on an analysis of reported data for a group of guideline publicly-traded companies that issued options with substantially similar terms. For this analysis, the Company selects companies with comparable characteristics including enterprise value, risk profiles, and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company determines expected volatility using a weighted average of the historical volatilities of the guideline group of companies. The Company expects to continue to apply this process until such time as it has adequate historical data regarding the volatility of its own traded stock price. As permitted under ASC 718, the Company has elected to use the contractual term as the expected term for certain non-employee awards, on an award-by-award basis. For all other awards, the expected term of the Company’s stock options has been determined utilizing the “simplified” method whereby the expected term equals the average of the vesting term and the original contractual term of the option, on a weighted basis based on the vesting of each tranche. The Company utilizes this method as it has insufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. 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 instruments with a term commensurate with the expected term assumption. The expected dividend yield is assumed to be zero as the Company has never paid dividends, and does not have current plans to pay any dividends on its common stock. The grant date fair value of restricted stock awards and restricted stock units is estimated based on the fair value of the Company's underlying common stock on the date of grant.
Retirement Plans	Retirement Plans The Company provided defined contribution plans to its employees beginning in 2021. In the U.S., the primary plan sponsored by the Company is a safe harbor, 401k plan with a 4% employer match, no waiting period and immediate vesting on the match. In the UK, the primary plan sponsored by the Company is a money purchase plan, which requires a minimum 8% contribution, including a minimum employer contribution of 4% and employee contribution of 4%.
Income Taxes	Income Taxes The Company follows the asset and liability method of accounting for income taxes under ASC 740, Income Taxes. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statements carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that included the enactment date. Valuation allowances are established, when necessary, to reduce deferred tax assets to the amount expected to be realized. The Company regularly assesses its ability to realize its deferred tax assets. Assessing the realization of deferred tax assets requires significant judgment. In determining whether its deferred tax assets are more likely than not realizable, the Company evaluated all available positive and negative evidence, and weighed the evidence based on its objectivity. After consideration of the evidence, the Company believes it would more likely than not be able to utilize existing loss carryforwards and research and development tax credits to offset future income in the United States. The operating entity in the United States has a history of cumulative net profits as it carries out services for other entities in the group and recognizes most of the interest income earned from cash, cash equivalents, and investments. ASC 740 prescribes a recognition threshold and a measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. The Company recognizes accrued interest and penalties related to unrecognized tax benefits as income tax expense. The Company is currently not aware of any issues under review that could result in significant payments, accruals or material deviation from its position. The Company is subject to income tax examinations by major taxing authorities since inception.
Net Loss Per Ordinary Share	Net Loss Per Ordinary Share Basic loss per ordinary share is computed by dividing net loss by the aggregate weighted-average number of ordinary shares outstanding. Diluted loss per ordinary share includes the effect, if any, from the potential exercise or conversion of securities, such as stock options, unvested restricted ordinary shares and restricted stock units which would result in the issuance of incremental ordinary shares. For diluted net loss per ordinary share, the weighted-average number of ordinary shares is the same for basic net loss per ordinary share due to the fact that when a net loss exists, dilutive securities are not included in the calculation as the impact is anti-dilutive.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In November 2024, the FASB issued ASU No. 2024-03, Income Statement - Reporting Comprehensive Income - Expense Recognition Disclosures. This ASU will require entities to provide enhanced disclosures related to certain expense categories included in income statement captions. The ASU aims to increase transparency and provide investors with more detailed information about the nature of expenses reported on the face of the income statement. The new standard does not change the requirements for the presentation of expenses on the face of the income statement. Under this ASU, entities are required to disaggregate, in a tabular format, expense captions presented on the face of the income statement - excluding earnings or losses from equity method investments - if they include any of the following expense categories: purchases of inventory, employee compensation, depreciation, intangible asset amortization, and depreciation or depletion. For any remaining items within each relevant expense caption, entities must provide a qualitative description of the nature of those expenses. The new ASU is effective for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of this standard on the related disclosures. In December 2023, the FASB issued ASU No. 2023-09, Improvements to Income Tax Disclosures. This ASU does not change accounting for income taxes but requires new disclosures focusing on two areas, the effective rate reconciliation and taxes paid. This new standard is effective for the Company for annual periods beginning after December 15, 2025. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of this standard on the related disclosures.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2025

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) promulgated by the Financial Accounting Standards Board (“FASB”). All intercompany accounts and transactions have been eliminated in consolidation.

Cash, Cash Equivalents, and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking accounts, certificates of deposit, money market funds and U.S. Treasury securities.

Restricted cash represents cash held to secure a letter of credit associated with the Company’s facility lease for its corporate headquarters. The Company had $0.7 million, in restricted cash as of December 31, 2025 and 2024, which was classified as Other non-current assets on the Company’s consolidated balance sheets.

Investments in Marketable Securities

The Company invests its excess cash in money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt securities and commercial paper. The Company’s investment policy limits investments to money market funds, certain types of debt securities issued by the U.S. Government and its agencies, corporate notes and commercial paper, and places restrictions on the credit ratings, maturities and concentration by type and issuer. Securities with original maturities of three months or less when purchased are included in cash and cash equivalents. We consider investments with original maturities greater than three months and remaining maturities less than one year to be short-term investments, while remaining maturities greater than one year are classified as long-term investments.

As of December 31, 2025, all investments in U.S. Treasury securities were classified as available-for-sale securities, which are recorded at fair value. Unrealized holding gains and losses on available-for-sale securities are reported net of related income taxes in accumulated other comprehensive income until realized. Purchase premiums and discounts are amortized to interest income over the terms of the related securities.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and investments. The Company’s cash, cash equivalents, and investments are held by financial institutions

primarily in the United States and the United Kingdom. Amounts on deposit may at times exceed federally insured limits. Management believes that the financial institutions are financially sound, and accordingly, the Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

Segments

Operating segments are defined as components of an enterprise with separate discrete information available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. We view our operations and manage our business as one segment.

Reclassifications

Certain amounts in the prior period financial statements have been reclassified to conform to the presentation of the current period financial statements. These reclassifications had no effect on previously reported net loss or comprehensive loss.

Foreign Currency Translation

The Company’s financial statements are presented in U.S. dollars (“USD”), the reporting currency of the Company. The functional currency of Centessa Pharmaceuticals plc is USD and the functional currency of the Centessa Subsidiaries is their respective local currency. Income and expenses have been translated into USD at average monthly exchange rates prevailing during the period. Assets and liabilities have been translated at the rates of exchange on the balance sheets dates and equity accounts at their respective historical rates. The resulting translation gain and loss adjustments are recorded directly as a separate component of shareholders’ equity as other comprehensive (loss) income.

Transactions denominated in a currency other than the functional currency are remeasured based upon the exchange rate at the date of remeasurement with the resulting gain or loss included in the accompanying consolidated statements of operations and comprehensive loss within Other non-operating income (expense), net.

Use of Estimates

The preparation of 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 revenues and expenses during the reporting periods. Significant areas that require management’s estimates include accrued research and development expenses, the note purchase agreement, research and development tax incentives and the recoverability of the Company’s net deferred tax assets and related valuation allowances. Estimates and assumptions 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.

Property and Equipment, net

Property and equipment are recorded at cost and are depreciated using the straight-line method over the estimated useful lives of the respective assets. Property and equipment includes computer equipment, furniture and office equipment, which have a useful life of three to seven years. The costs of maintenance and repairs are expensed as incurred. Improvements and betterment that add new functionality or extend the useful life of the asset are capitalized.

Capitalized software as a service costs representing costs incurred during the application development stage are included in “Other non-current assets” and the corresponding current portion, in “Prepaid expenses and other current assets” and is amortized using the straight line method over 5 years. Costs incurred during the preliminary project stage and the post-implementation-operation stage are expensed as incurred. Hosting fees associated with the hosting as a service

arrangement are expensed on a straight line basis over the term of the hosting arrangement.

Leases

In accordance with ASU No. 2016-02, Leases (“ASC 842”), the Company assesses whether an arrangement is a lease, or contains a lease at the inception of the arrangement. When an arrangement contains a lease, the Company categorizes leases with contractual terms longer than twelve months as either operating or finance. Finance leases are generally those leases that allow us to substantially utilize or pay for the entire asset over its estimated life. Assets acquired under finance leases are recorded in “Property and equipment, net.” All other leases are categorized as operating leases.

The Company records right-of use ("ROU") assets and lease obligations for its finance and operating leases, which are initially recognized based on the discounted future lease payments over the term of the lease. As the rate implicit in the Company's leases may not be easily determinable, the Company uses its incremental borrowing rate to calculate the present value of the sum of the lease payments. Lease terms may include options to extend or terminate the lease. The Company will include such options in determining the lease term when it is reasonably certain that the Company will exercise such options. Operating and finance lease ROU assets are recognized net of any lease prepayments and incentives. The Company elected the practical expedient to not separate lease and non-lease components and, accordingly, accounts for them as a single lease component. Operating lease expense is recognized on a straight-line basis over the lease term. Finance lease expense is recognized based on the effective-interest method over the lease term. The Company elected not to recognize ROU assets and lease obligations for any short-term leases, which are defined as leases with an initial term of 12 months or less.

Long-Lived Assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated undiscounted future cash flows, then an impairment charge is recognized for the amount by which the carrying value of the asset exceeds the estimated fair value of the asset. As of December 31, 2025, the Company believes that no revision of the remaining useful lives or write-down of long-lived assets is required.

Fair Value Measurement

Fair value is the price that could be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value determination in accordance with applicable accounting guidance requires that a number of significant judgments be made. Additionally, fair value is used on a nonrecurring basis to evaluate assets for impairment or as required for disclosure purposes by applicable accounting guidance on disclosures about fair value of financial instruments. Depending on the nature of the assets and liabilities, various valuation techniques and assumptions are used when estimating fair value. The carrying amounts of certain of the Company’s financial instruments, including cash and cash equivalents, prepaid expense and accounts payable, are shown at cost, which approximates fair value due to the short-term nature of these instruments. The Company follows the provisions of FASB ASC Topic 820, Fair Value Measurement, for financial assets and liabilities measured on a recurring basis. The guidance requires fair value measurements be classified and disclosed in one of the following three categories:

Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.

Level 2: Quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liabilities.

Level 3: Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity).

Debt Issuance Costs

For debt issuances that are not accounted for under the fair value option, such as the Loan and Security Agreement, any debt issuance costs are capitalized, recorded as an offset to the Company’s debt balances and amortized as interest expense over the term of the associated debt instrument using the effective interest method. If the maturity of the debt is accelerated as a result of default or early debt repayment, the amortization would then be accelerated. Amounts paid related to debt financing activities are presented on the consolidated balance sheet as a direct deduction from the debt liability.

License and other revenue

The Company recognizes revenues from collaboration, license or other research or sale arrangements when or as performance obligations are satisfied. For milestone payments, the Company assesses, at contract inception, whether the milestones are considered probable of being achieved. If it is probable that a significant revenue reversal will occur, the Company will not record revenue until the uncertainty has been resolved. Milestone payments that are contingent upon regulatory approval are not considered probable until the approvals are obtained as it is outside of the control of the Company. If it is probable that significant revenue reversal will not occur, the Company will estimate the milestone payments using the most likely amount method. The Company reassesses the milestones each reporting period to determine the probability of achievement. Any potential consideration received in the form of royalty or sales-based milestones will be recorded when the customer’s subsequent sales or usages occur. For accounting treatment related to the Genmab agreement, see Note 3 - “Revenue Recognition”.

Collaborative Arrangements

The Company enters into collaborative arrangements to develop and commercialize intellectual property. These arrangements typically involve two (or more) parties who are active participants in the collaboration and are exposed to significant risks and rewards dependent on the commercial success of the activities. These collaborations usually involve various activities by one or more parties, including research and development, marketing and selling and distribution. Often, these collaborations require upfront, milestone and royalty or profit share payments, contingent upon the occurrence of certain future events linked to the success of the asset in development. Amounts due to collaborative partners related to development activities are generally reflected as research and development expense.

Research and Development Expenses and Accruals and Research and Development Tax Incentives

Research and Development Expenses and Accruals

All research and development costs are expensed in the period incurred and consist primarily of salaries, payroll taxes, employee benefits, stock-based compensation charges for those individuals involved in research and development efforts, third-party license fees, external research and development costs incurred under agreements with contract research organizations and consultants to conduct and support the Company’s ongoing clinical trials as well as external costs of outside vendors engaged to manufacture research and development materials.

The Company has entered into various research and development contracts with clinical research organizations, clinical development and manufacturing organizations and other companies. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred. Payments made in advance of performance are reflected in the accompanying balance sheets as prepaid expenses, while payments made after performance are reflected as accrued liabilities in the accompanying balance sheets. The Company records accruals for estimated costs incurred for ongoing research and development activities. When recording accruals for ongoing research and development activities, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Nonrefundable advance payments for goods and services, including fees for process development or manufacturing and distribution of clinical supplies that will be used in future research and development activities, are recognized as expense in the period that the related goods are consumed or services are performed.

Milestone payments within the Company’s licensing arrangements are recognized when achievement of the milestone is deemed probable to occur. To the extent products are commercialized and future economic benefit has been established, commercial milestones that become probable are capitalized and amortized over the estimated remaining useful life of the intellectual property. Significant judgments and estimates may be made in determining the prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates.

Research and Development Tax Incentives

The Company participates in research tax incentive programs that are granted to companies by the United Kingdom tax authorities in order to encourage them to conduct technical and scientific research. Expenditures that meet the required criteria are eligible to receive a tax credit that is reimbursed in cash, upon surrender of loss carryforwards. Estimates of the amount of the cash refund expected to be received are determined at each reporting period and recorded as reductions to research and development expenses. The Company recorded research and development tax incentives of $22.7 million and $30.9 million during the years ended December 31, 2025 and December 31, 2024, respectively.

Through December 31, 2024, the Company claimed relief under the Small and Medium Enterprise (“SME”) scheme. Beginning January 1, 2025, changes to the program in the UK have aligned the tax incentives earned for SME and large entities. The merged scheme provides relief for qualifying R&D expenditure. If the company is loss-making, a cash credit can be obtained. If the company continues to meet the SME thresholds and is loss making, then a higher rate of credit may be available under the new Enhanced R&D Intensive Support (ERIS). The Company expects eligible R&D expenditures qualifying for the credit outside of the UK will be more limited as a result of these legislative changes and it expects to recognize less tax incentives in the United Kingdom.

Share-Based Compensation

The Company measures share-based awards, including restricted shares, restricted stock units and stock options, at their grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards. The Company determines the fair value of share-based compensation awards using the market closing price of the Company’s ADSs on the date of grant. Forfeitures of stock options are recognized in the period the forfeiture occurs.

The Company classifies stock-based compensation expense in its consolidated financial statement of operations in the same manner in which the award recipient’s salary or service payments are classified.

The fair value of each stock option awards is estimated on the date of grant using the Black-Scholes option pricing model, which requires inputs of subjective assumptions, including: (i) the expected volatility of the Company’s stock; (ii) the expected term of the award; (iii) the risk-free interest rate; and (iv) expected dividends. Due to the lack of Company-specific historical and implied volatility data, the Company determines the volatility for awards granted based on an analysis of reported data for a group of guideline publicly-traded companies that issued options with substantially similar terms. For this analysis, the Company selects companies with comparable characteristics including enterprise value, risk profiles, and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company determines expected volatility using a weighted average of the historical volatilities of the guideline group of companies. The Company expects to continue to apply this process until such time as it has adequate historical data regarding the volatility of its own traded stock price. As permitted under ASC 718, the Company has elected to use the contractual term as the expected term for certain non-employee awards, on an award-by-award basis. For all other awards, the expected term of the Company’s stock options has been determined utilizing the “simplified” method whereby the expected term equals the average of the vesting term and the original contractual term of the option, on a weighted basis based on the vesting of each tranche. The Company utilizes this method as it has insufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. 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 instruments with a term commensurate with the expected term assumption. The expected dividend yield is assumed to be zero as the Company has never paid dividends, and does not have current plans to pay any dividends on its common stock.

The grant date fair value of restricted stock awards and restricted stock units is estimated based on the fair value of the Company's underlying common stock on the date of grant.

Retirement Plans

The Company provided defined contribution plans to its employees beginning in 2021. In the U.S., the primary plan sponsored by the Company is a safe harbor, 401k plan with a 4% employer match, no waiting period and immediate vesting on the match. In the UK, the primary plan sponsored by the Company is a money purchase plan, which requires a minimum 8% contribution, including a minimum employer contribution of 4% and employee contribution of 4%.

Income Taxes

The Company follows the asset and liability method of accounting for income taxes under ASC 740, Income Taxes. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statements carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that included the enactment date. Valuation allowances are established, when necessary, to reduce deferred tax assets to the amount expected to be realized.

The Company regularly assesses its ability to realize its deferred tax assets. Assessing the realization of deferred tax assets requires significant judgment. In determining whether its deferred tax assets are more likely than not realizable, the Company evaluated all available positive and negative evidence, and weighed the evidence based on its objectivity. After consideration of the evidence, the Company believes it would more likely than not be able to utilize existing loss carryforwards and research and development tax credits to offset future income in the United States. The operating entity in the United States has a history of cumulative net profits as it carries out services for other entities in the group and recognizes most of the interest income earned from cash, cash equivalents, and investments.

ASC 740 prescribes a recognition threshold and a measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. The Company recognizes accrued interest and penalties related to unrecognized tax benefits as income tax expense. The Company is currently not aware of any issues under review that could result in significant payments, accruals or material deviation from its position. The Company is subject to income tax examinations by major taxing authorities since inception.

Net Loss Per Ordinary Share

Basic loss per ordinary share is computed by dividing net loss by the aggregate weighted-average number of ordinary shares outstanding. Diluted loss per ordinary share includes the effect, if any, from the potential exercise or conversion of securities, such as stock options, unvested restricted ordinary shares and restricted stock units which would result in the issuance of incremental ordinary shares. For diluted net loss per ordinary share, the weighted-average number of ordinary shares is the same for basic net loss per ordinary share due to the fact that when a net loss exists, dilutive securities are not included in the calculation as the impact is anti-dilutive.

Recently Issued Accounting Pronouncements

In November 2024, the FASB issued ASU No. 2024-03, Income Statement - Reporting Comprehensive Income - Expense Recognition Disclosures. This ASU will require entities to provide enhanced disclosures related to certain expense categories included in income statement captions. The ASU aims to increase transparency and provide investors with more detailed information about the nature of expenses reported on the face of the income statement. The new standard does not change the requirements for the presentation of expenses on the face of the income statement. Under this ASU, entities are required to disaggregate, in a tabular format, expense captions presented on the face of the income statement - excluding

earnings or losses from equity method investments - if they include any of the following expense categories: purchases of inventory, employee compensation, depreciation, intangible asset amortization, and depreciation or depletion. For any remaining items within each relevant expense caption, entities must provide a qualitative description of the nature of those expenses. The new ASU is effective for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of this standard on the related disclosures.

In December 2023, the FASB issued ASU No. 2023-09, Improvements to Income Tax Disclosures. This ASU does not change accounting for income taxes but requires new disclosures focusing on two areas, the effective rate reconciliation and taxes paid. This new standard is effective for the Company for annual periods beginning after December 15, 2025. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of this standard on the related disclosures.