Intangible assets, net, consisted of the following (in thousands):


		As of December 31, 2023
	Estimated Useful Life	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Royalty rights	3 - 13 years	$	3,494	$	(150	)	$	3,344
IPR&D	Indefinite		20,964		—			20,964
Total		$	24,458	$	(150	)	$	24,308

As described in Note 4, Licensing Agreements, the Company assumed all out-licensing agreements of Apexigen upon the completion of the Merger and retains royalty rights under certain Apexigen agreements. The Company recognized a definite-lived intangible asset related to these royalty rights, which was valued using the income approach and adjusted for any potential repayment provisions.

Royalty rights are amortized on a straight-line basis over its useful lives, which are 3- and 13-years, and was determined based on the terms and conditions underlying the licensing agreements and the expected use of the asset by the Company. Useful lives are periodically evaluated to determine whether events or circumstances have occurred which indicate the need for revision.

The weighted-average amortization period of the acquired royalty rights is approximately 8.3 years. Amortization expense was $0.2 million for the year ended December 31, 2023 and was recorded as part of “Research and development” within the accompanying consolidated statements of operations and comprehensive loss. Amortization of intangible assets for the next five years related to the intangible assets held as of December 31, 2023 is estimated to be as follows (in thousands):


Years Ending December 31,	Estimated Amortization Expense
2024	$	421
2025		421
2026		322
2027		223
2028		223
Thereafter		1,734
Total	$	3,344

IPR&D represents the research and development assets of Apexigen acquired by the Company, which were in-process, but not yet completed, and which the Company has the opportunity to advance. The primary basis for determining the completion of these projects is obtaining regulatory approval to market the underlying products in an applicable geographic region. IPR&D becomes definite-lived upon the completion or abandonment of the associated research and development efforts.