Caribou CMO awarded options and sells for taxes

Caribou Biosciences Chief Medical Officer Tina M. Albertson reported a mix of equity grants and a small tax-related sale.

Rhea-AI Filing Summary

Caribou Biosciences Chief Medical Officer Tina M. Albertson reported a mix of equity grants and a small tax-related sale. She received 55,000 shares of common stock as restricted stock units that vest annually over four years starting on February 20, 2027. She was also granted an option for 247,500 shares of common stock, vesting monthly so that it is fully vested by February 20, 2030.

Separately, 1,066 common shares were sold at $1.96 per share in a sell-to-cover transaction to satisfy tax withholding on previously vested RSUs under a pre-established Rule 10b5-1 trading plan. After these transactions, she directly holds 68,523 common shares.

Insider Trade Summary

Net Seller: 1,066 shares

Net Sell 3 txns

Insider Albertson Tina M.

Role Chief Medical Officer

Sold 1,066 shs ($2K)

Type	Security	Shares	Price	Value
Sale	Common Stock	1,066	$1.96	$2K
Grant/Award	Option to purchase Common Stock	247,500	$0.00	$0.00
Grant/Award	Common Stock	55,000	$0.00	$0.00

Holdings After Transaction: Option to purchase Common Stock — 247,500 contracts (Direct); Common Stock — 68,523 shares (Direct)

Footnotes (3)

1. F1. This reflects restricted stock units ("RSUs") that vest in four equal annual installments beginning on February 20, 2027, subject to the reporting person continuing to provide service to the Issuer through the applicable vesting dates. The RSUs will be settled in stock within 30 days after each vesting date.
2. F2. Reflects the number of shares of common stock that were sold in a "sell-to-cover" transaction for the sole purpose of satisfying tax withholding obligations in connection with the vesting of RSUs previously granted to the reporting person and does not represent a discretionary trade by the reporting person. This transaction was made pursuant to a Rule 10b5-1 trading plan in the form of a durable sell-to-cover instruction adopted by the reporting person on August 12, 2024. The trading plan provides for the automatic sale of shares of common stock necessary to satisfy the reporting person's tax withholding obligations incurred in connection with the vesting of RSUs.
3. F3. 1/48 of the total number of shares subject to this option will vest on each monthly anniversary of the grant date such that the option will be fully vested on February 20, 2030, subject to the reporting person continuing to provide service to the Issuer through each such vesting date.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transactions did Caribou Biosciences (CRBU) report for its CMO?

Caribou Biosciences reported equity grants and a small tax sale for Chief Medical Officer Tina M. Albertson. She received RSUs and stock options and sold 1,066 shares only to cover tax withholding on previously vested RSUs under a Rule 10b5-1 plan.

How many RSUs did the Caribou Biosciences (CRBU) CMO receive?

The CMO received 55,000 restricted stock units (RSUs). These RSUs vest in four equal annual installments beginning on February 20, 2027, provided she continues to serve Caribou Biosciences, and will be settled in stock within 30 days after each vesting date.

What stock options were granted to the Caribou Biosciences (CRBU) CMO?

The CMO was granted an option for 247,500 shares of common stock. One forty-eighth of the option vests monthly from the grant date, with full vesting expected by February 20, 2030, contingent on continued service with Caribou Biosciences.

Why did the Caribou Biosciences (CRBU) CMO sell 1,066 shares?

The 1,066 shares were sold solely to cover tax withholding linked to vested RSUs. The sale occurred at $1.96 per share under a durable Rule 10b5-1 sell-to-cover instruction, and is described as non-discretionary rather than an elective open-market sale.

How many Caribou Biosciences (CRBU) shares does the CMO hold after these transactions?

After the reported transactions, the CMO directly holds 68,523 common shares of Caribou Biosciences. This figure reflects the net position after receiving stock and option awards and completing a small sell-to-cover transaction to meet tax obligations on RSU vesting.

When will the Caribou Biosciences (CRBU) CMO’s RSUs and options fully vest?

The RSUs are scheduled to fully vest by 2030. RSUs vest in four annual installments starting February 20, 2027, while the 247,500-share option vests monthly so that it is fully vested on February 20, 2030, assuming continued service.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 02/24/2026 - 08:53 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Albertson Tina M.

(Last) (First) (Middle)

C/O CARIBOU BIOSCIENCES, INC.

2929 7TH STREET, SUITE 105

(Street)

BERKELEY CA 94710

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Caribou Biosciences, Inc. [ CRBU ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Medical Officer

3. Date of Earliest Transaction (Month/Day/Year)
02/20/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	02/20/2026		A		55,000(1)	A	$0	69,589	D
Common Stock	02/24/2026		S(2)		1,066(2)	D	$1.96	68,523	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Option to purchase Common Stock	$1.8	02/20/2026		A		247,500		(3)	02/19/2036	Common Stock	247,500	$0	247,500	D

Explanation of Responses:

1. This reflects restricted stock units ("RSUs") that vest in four equal annual installments beginning on February 20, 2027, subject to the reporting person continuing to provide service to the Issuer through the applicable vesting dates. The RSUs will be settled in stock within 30 days after each vesting date.

2. Reflects the number of shares of common stock that were sold in a "sell-to-cover" transaction for the sole purpose of satisfying tax withholding obligations in connection with the vesting of RSUs previously granted to the reporting person and does not represent a discretionary trade by the reporting person. This transaction was made pursuant to a Rule 10b5-1 trading plan in the form of a durable sell-to-cover instruction adopted by the reporting person on August 12, 2024. The trading plan provides for the automatic sale of shares of common stock necessary to satisfy the reporting person's tax withholding obligations incurred in connection with the vesting of RSUs.

3. 1/48 of the total number of shares subject to this option will vest on each monthly anniversary of the grant date such that the option will be fully vested on February 20, 2030, subject to the reporting person continuing to provide service to the Issuer through each such vesting date.

Remarks:

	/s/ Barbara G. McClung, as attorney-in-fact	02/24/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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