Caribou Biosciences, Inc.

Rule 10b5-1 Trading Arrangements

On February 25, 2026, Tim Kelly, M.B.A., ourchief technology officer, entered into a “Rule 10b5-1 trading arrangement” (as that term is defined in Regulation S-K, Item 408) that is intended to qualify as an “eligible sell-to-cover transaction” (as described in Rule 10b5-1(c)(1)(ii)(D)(3) under the Securities Exchange Act of 1934, as amended (“Exchange Act”)) and is intended to satisfy the affirmative defense in Rule 10b5-1(c) under the Exchange Act. This sell-to-cover arrangement applies to restricted stock units or performance-based stock units (collectively, “RSUs”), whether vesting is based on the passage of time and/or the achievement of performance goals, that were previously granted or that could in the future be granted by us from time to time (this type of arrangement, with the attributes described in this paragraph, is referred to as an “RSU Sell-to-Cover Instruction”). An RSU Sell-to-Cover Instruction provides for the automatic sale of shares of common stock that would otherwise be issuable on each settlement date of a covered RSU in an amount necessary to satisfy the applicable tax withholding obligations, with the proceeds of the sale delivered to us in satisfaction of the applicable tax withholding obligations. The number of shares of common stock that will be sold under an RSU Sell-to-Cover Instruction is not currently determinable as the number will vary based on the extent to which vesting conditions are satisfied, the market price of our common stock at the time of settlement, and the potential future grant of RSUs subject to a RSU Sell-to-Cover Instruction. An RSU Sell-to-Cover Instruction will remain in place indefinitely unless revoked in writing (including as to any particular sell-to-cover sale, as to which the officer may elect to pay the applicable withholding taxes in cash) in accordance with its terms.

Except as described above, no other Section 16 officer or director adopted orterminated any Rule 10b5-1 trading arrangement or non-Rule 10b5-1 trading arrangement (as that term is defined in Regulation S-K, Item 408) during the quarter ended March 31, 2026.