Income taxes (Tables)

12 Months Ended

Mar. 31, 2026

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)