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Income taxes (Tables) | 12 Months Ended
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Mar. 31, 2026
Income Tax Disclosure [Abstract] |
Schedule of net loss before income taxes | Loss before income taxes for the years ended March 31, 2026 and 2025 were as follows:
| Year ended March 31,
| 2026 |  | 2025
United States | (66,042) |  |  | (25,870) |
United Kingdom | (248,449) |  |  | (220,959) |
Total | $ | (314,491) |  |  | $ | (246,829) |
Schedule of components of income tax expense (benefit) | Income tax (benefit) expense consisted of the following:
| Year ended March 31,
| 2026 |  | 2025
Current income tax (benefit) provision: |  |  |
Federal | $ | (313) |  |  | $ | 468 |
State | (238) |  |  | — |
Foreign (United Kingdom) | — |  |  | — |
Total current income tax (benefit) provision: | $ | (551) |  |  | $ | 468 |
Schedule of reconciliation of the U.S federal statutory income tax rate | A reconciliation of taxes at the U.S. federal statutory income tax rate to the Company’s benefit from income taxes for the year ended March 31, 2026 in accordance with the guidance upon adoption of ASU 2023-09 is as follows:
| Year Ended March 31,
| 2026
| Amount |  | Percent
Pre tax loss | $ | (314,491) |  |  |
U.S. Federal statutory tax rate | (66,043) |  |  | 21.0 | %
State and local income taxes, net of federal benefit | (2,516) |  |  | 0.8 | %
Foreign tax effects: |  |  |
United Kingdom |  |  |
Change in valuation allowance | 63,295 |  |  | (20.1) | %
Statutory tax rate difference between U.K. and U.S. | (9,938) |  |  | 3.2 | %
Other | (1,186) |  |  | 0.4 | %
Tax credits: |  |  |
Federal R&D credit | (15,381) |  |  | 4.9 | %
Change in valuation allowance | 20,265 |  |  | (6.4) | %
Nontaxable or nondeductible items: |  |  |
Other | (788) |  |  | 0.3 | %
Stock compensation | 2,204 |  |  | (0.7) | %
Changes in unrecognized tax benefits | 9,537 |  |  | (3.0) | %
Total | $ | (551) |  |  | 0.2 | %
The Company's effective tax rate includes the effects of state and local income taxes, net of the federal income tax benefit, which are primarily attributable to Massachusetts, where the Company has significant business activities. Massachusetts has a higher effective tax rate compared to other jurisdictions where the Company operates, and together, accounts for more than half of the Company's total state tax benefit. The reconciliation of taxes at the federal statutory rate to our provision for (benefit from) income taxes for the year ended March 31, 2025 in accordance with the guidance prior to the adoption of ASU 2023-09 was as follows:
|  | Year Ended March 31,
|  | 2025
U.S. federal statutory income tax rate |  | (21.0) | %
State taxes, net of federal benefit |  | (0.5) | %
Research and development |  | (1.6) | %
Stock compensation |  | 1.2 | %
Foreign tax rate differential |  | (3.6) | %
Change in tax rates |  | 0.4 | %
Change in valuation allowance |  | 24.3 | %
Other |  | 1.0 | %
|  | 0.2 | %
Schedule of components of deferred tax assets and liabilities | The components of the Company’s deferred tax assets as of March 31, 2026 and 2025 were as follows:
| Year Ended March 31,
| 2026 |  | 2025
Deferred tax assets: |  |  |
Net operating loss carryforwards | $ | 267,196 |  |  | $ | 192,909 |
Research and development credits | 15,144 |  |  | 2,676 |
Property, plant and equipment | 4,735 |  |  | 4,596 |
Capitalized start-up costs | 873 |  |  | 1,014 |
Stock compensation | 20,297 |  |  | 16,478 |
Accrued expenses | 5,595 |  |  | 6,397 |
Lease liability | 6,931 |  |  | 7,318 |
Other | 120 |  |  | — |
Total deferred tax assets | 320,891 |  |  | 231,388 |
Valuation allowance | (312,035) |  |  | (221,629) |
Net deferred tax assets | 8,856 |  |  | 9,759 |
Deferred tax liabilities: |  |  |
Right of use asset | (8,856) |  |  | (9,698) |
Other | — |  |  | (61) |
Total deferred tax liabilities | (8,856) |  |  | (9,759) |
Net deferred tax assets (liabilities) | $ | — |  |  | $ | — |
Schedule of changes in the valuation allowance for deferred tax assets | Changes in the valuation allowance for deferred tax assets during the years ended March 31, 2026 and 2025 related primarily to the increase in net operating loss carryforwards were as follows:
| Year Ended March 31,
| 2026 |  | 2025
Valuation allowance as of beginning of year | $ | 221,629 |  |  | $ | 161,890 |
Increases recorded to income tax provision | 90,329 |  |  | 59,848 |
(Decreases) increases recorded to equity | 77 |  |  | (109) |
Valuation allowance as of end of year | $ | 312,035 |  |  | $ | 221,629 |
Schedule of unrecognized tax benefits | Changes in the Company's gross unrecognized tax benefits from uncertain tax positions, excluding interest and penalties, consisted of the following:
| Year Ended March 31,
| 2026 |  | 2025
Unrecognized tax benefits - beginning of year | $ | 10,443 |  |  | $ | 8,667 |
Increases for tax positions taken during current years | 4,874 |  |  | 921 |
Increases (decreases) for tax positions taken during prior years | 5,252 |  |  | 855 |
Unrecognized tax benefits - end of year | $ | 20,569 |  |  | $ | 10,443 |
Schedule of cash flow, supplemental disclosures | The following summarizes the Company's income taxes paid, net of refunds received, for the year presented below:
| Year Ended March 31,
| 2026
Federal | $ | 130 |
State |
Massachusetts | (135) |
Foreign | — |
Total | $ | (5) |

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