In February 2022 and subsequently amended in June 2023, the Company entered into an agreement to lease approximately 140,000 square feet of office, general laboratory and manufacturing space at 840 Winter Street in Waltham, Massachusetts (the “840 Winter Lease”). On February 18, 2025, the Company entered into a Second Amendment (the “Winter Street Amendment”) that amends the 840 Winter Lease. Pursuant to the Winter Street Amendment, the 840 Winter Lease will terminate on or before June 30, 2028. In connection with the Winter Street Amendment, the Company will pay to the landlord lease modification payments totaling $78.0 million in three installments, with the first $34.0 million being paid in February 2025, a second $30.0 million payment in April 2025 and the remaining $14.0 million payment in January 2026. The Company is not subject to paying any base rent, operating expenses or other costs pursuant to the 840 Winter Lease after January 2025. In conjunction with the Winter Street Amendment, also on February 18, 2025, the Company entered into a Lease Agreement (the “Tech Square Lease”) with the same landlord as the 840 Winter Lease, for office and laboratory space located at 400 Technology Square, Cambridge, Massachusetts (“400 Tech Square”).

Under the terms of the Tech Square Lease, the Company will initially lease approximately 101,000 square feet at 400 Technology Square (the “Initial Tech Square Premises”). In addition, the Tech Square Lease will expand, in two tranches, to include approximately 46,000 square feet of additional office and laboratory space at 400 Tech Square (the “Additional Tech Square Premises”) when each such space becomes available. On July 1, 2025, the landlord will deliver the Initial Tech Square Premises to the Company for the Company’s construction of tenant improvements (the “Delivery Date”). The Company’s obligation to pay rent will start on the date that is approximately 14 months after the Delivery Date (the “Rent Commencement Date”). The initial term of the Tech Square Lease is twelve years and three months following the Rent Commencement Date, and the Company has an option to extend the Tech Square Lease for an additional term of five years. As of the Rent Commencement Date, the base rent under the Tech Square Lease is expected to be $108.00 per square foot per year, plus certain operating expenses and taxes. The base rent is subject to scheduled annual increases of 3% on the anniversary of the Delivery Date. In addition, the Company is entitled to receive up to $41.5 million of tenant improvement allowances for the Initial Tech Square Premises, and additional tenant allowances for the Additional Tech Square Premises. The construction of tenant improvements will be primarily funded by the tenant improvement allowance and is expected to be completed in the second half of 2026.

The Company accounted for the Winter Street Amendment and Tech Square Lease as one combined contract under ASC 842, Leases (Topic 842). The Company identified two lease components, 840 Winter and 400 Tech Square. The total consideration in the combined contract is $244.4 million, which includes the undiscounted remaining lease payments of the 840 Winter and 400 Tech Square components and the lease prepayments. The Company did not include the lease payments associated with the five-year extension option related to the Tech Square Lease as it is not reasonably certain of exercise. The Company allocated

$52.1 million to the 840 Winter component and $192.3 million to the 400 Tech Square component based on relative standalone selling prices.

The Company accounted for the 840 Winter component as a lease modification as of February 18, 2025. The Company remeasured the lease liability as of the modification date based on the remaining lease payments and using an updated incremental borrowing rate of 6.6%, which resulted in a $61.9 million decrease in the lease liability and a corresponding decrease in the right of use asset. The Company recorded a modified lease liability of $46.5 million and a right of use asset of $50.0 million for the 840 Winter component. As of March 31, 2025, the lease liability and right-of-use asset were $27.9 million and $48.3 million, respectively.

As of March 31, 2025, the Tech Square component has not commenced as the Company has not taken control over the premises and therefore the Company did not record a right-of-use asset or lease liability. The Company has recorded $26.8 million of prepaid rent related to the Tech Square component within “Investments and other assets” on the condensed consolidated balance sheets as of March 31, 2025.

The table below reconciles the undiscounted cash flows for each of the next five years and total of the remaining years to the operating lease liabilities recorded in the condensed consolidated balance sheet as of March 31, 2025 for all of the Company’s leases.


Future Operating Lease Payments
Year Ending December 31,	(in thousands)
Remainder of 2025	$	31,489
2026		32,219
2027		24,125
2028		15,637
2029		12,666
Thereafter		26,593
Total lease payments	$	142,729
Less: imputed interest		(23,476	)
Total operating lease liabilities at March 31, 2025	$	119,253

Excluded from the table above are $165.5 million of undiscounted future operating lease payments for the Tech Square Lease that have not commenced as of March 31, 2025.