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Sale of Future IMDELLTRA® Royalties
 3 Months Ended
Mar. 31, 2026
Debt Disclosure [Abstract]  
Sale of Future IMDELLTRA® Royalties Sale of Future IMDELLTRA® Royalties
On August 25, 2025, the Company entered into an agreement (the “Royalty Agreement”) to sell its royalty rights on the worldwide sales, excluding China, of Amgen’s IMDELLTRA® (tarlatamab-dlle) for up to $950,000 to Royalty Pharma Investments 2023 ICAV (“Royalty Pharma”). Under the terms of the Royalty Agreement, the Company received a non-refundable upfront payment of $885,000 upon closing of the Royalty Agreement. Subsequently, the Company exercised its option to sell additional royalties to Royalty Pharma and received $26,000 in the fourth quarter of 2025. The Company will share in a portion of the royalty on annual sales above $1.5 billion, and will maintain royalty and all other rights to other assets under the terms of its collaboration agreement with Amgen.
The Company evaluated the arrangement and determined that the proceeds from the sale of future IMDELLTRA® royalties, as well as the option to sell remaining royalties when and if exercised, should be treated as a financing liability according to ASC 470, Debt due to the Company’s continuing involvement with the Amgen collaboration. At the transaction date, the Company recognized the upfront proceeds received from Royalty Pharma of $885,000 and, subsequently, the option proceeds of $26,000, as liabilities and is amortizing them using the effective interest method over the life of the arrangement. The Company imputes interest expense associated with the liability using the effective interest rate method. The effective interest rate is the rate that equates the present value of the estimate of remaining royalty revenues payable to Royalty Pharma with the carrying amount of the liability. The interest rate on the sale of future royalty liability may vary during the term of the agreement depending on a number of factors, including the royalty revenues forecast. The Company evaluates the interest rate quarterly based on its expectations of future royalty revenues, historical experience and current market conditions using the prospective method. A significant increase or decrease in future royalty revenues will materially impact the timing of royalty sale liability amortization, interest expense and the time period for repayment. The Company will assess the expected payments to Royalty Pharma quarterly, and, to the extent the amount or timing of such payments is materially different than its initial estimates, the Company will prospectively adjust the amortization of the liability and the related interest expense.
The repayment of this obligation to Royalty Pharma will be made upon the receipt of royalties from Amgen throughout the royalty period. The repayment does not follow a fixed repayment schedule and will be recognized over the life of the royalty stream, which is expected to occur through at least 2041. The Royalty Agreement also contains customary representations, warranties, covenants, and indemnification provisions.

As of March 31, 2026 and December 31, 2025, the royalty financing obligation recorded in the Company’s balance sheet was as follows:
 As of
March 31,December 31,
 20262025
 $$
Sale of future royalty liability, current portion72,735 56,714 
Sale of future royalty liability, non-current portion831,664 850,242 
Total sale of future royalty liability904,399 906,956 
The following table summarizes the royalty sale liability activity during the three months ended March 31, 2026:
 Royalty Sale Liability
 $
Balance at December 31, 2025
906,956 
Debt portion of royalties recognized and settled to Royalty Pharma(2,557)
Balance at March 31, 2026
904,399 
The carrying value of the sale of future royalty liability approximates fair value as of March 31, 2026 and is based on the Company’s current estimates of future royalties expected to be paid to Royalty Pharma over the life of the royalty stream, which are considered Level 3 inputs.
Interest expense related to this arrangement was as follows:
Three Months Ended
March 31,
20262025
$$
Interest expense18,496 — 
As of March 31, 2026, $18,496 of interest expense was accrued. The effective annual imputed interest rate was 8.2% as of March 31, 2026.