X0609 4 2026-03-05 0 0000730272 REPLIGEN CORP RGEN 0001991429 Hughes Violetta false C/O REPLIGEN CORPORATION 41 SEYON ST., BLDG 1, STE 100 WALTHAM MA 02453 0 1 0 0 CHIEF ACCOUNTING OFFICER 0 Common Stock 2026-03-05 4 A 0 2466 0 A 6608 D Common Stock 2026-09-01 4 F 0 277 170.02 D 6331 D Ms. Hughes was awarded 2,466 restricted stock units. Each restricted stock unit represents a contingent right to receive one share of Repligen Corporation's Common Stock. The restricted stock units vest in equal annual installments over a four-year period beginning on the first anniversary of the grant date. The restricted stock units may be settled only by delivering shares of Repligen Corporation's Common Stock, and thus, the grant is being reported in Table 1 as allowed per SEC guidance. Represents the number of shares withheld by the Issuer to satisfy the tax withholding obligations of the reporting person that arose upon the release of restricted stock units. /s/ Meghan Stapleton (Attorney in Fact) 2026-09-02