X0609 4 2026-10-06 0 0000730272 REPLIGEN CORP RGEN 0002104618 Douglass Brian Robb false C/O REPLIGEN CORPORATION 41 SEYON ST., BLDG 1, STE 100 WALTHAM MA 02453 0 1 0 0 CHIEF PRODUCT OFFICER 0 Common Stock 2026-10-06 4 A 0 700 0 A 8685 D Stock Option (Right to Buy) 174.86 2026-10-06 4 A 0 675 0 A 2036-10-06 Common Stock 675 675 D Mr. Douglass was awarded 700 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 three-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. 225 shares will vest on each of October 6, 2027, October 6, 2028, and October 6, 2029. /s/ Meghan Stapleton (Attorney in Fact) 2026-10-08