Korro Bio director sells 48,690 shares at ~$14

Rhea-AI Filing Summary

Korro Bio, Inc. (KRRO) reported that director Jean Francois Formela filed a Form 4 disclosing indirect sales of an aggregate 48,690 shares of common stock on September 11 and September 14, 2026, at weighted average prices around $14 per share, executed pursuant to a Rule 10b5-1 trading plan.

The transactions were carried out by investment entities Atlas Venture Fund XI, L.P. and Atlas Venture Opportunity Fund II, L.P.; Formela is a member of their general partners and disclaims Section 16 beneficial ownership of these shares except to the extent of any pecuniary interest.

Insider Trade Summary 10b5-1

Net Seller: 48,690 shares

Net Sell 4 txns

Insider FORMELA JEAN FRANCOIS

Role Director

Sold 48,690 shs ($686K)

Type	Security	Shares	Price	Value
Sale	Common Stock F1, F5, F3	31,888	$14.12	$450K
Sale	Common Stock F1, F5, F4	6,602	$14.12	$93K
Sale	Common Stock F1, F2, F3	8,450	$13.99	$118K
Sale	Common Stock F1, F2, F4	1,750	$13.99	$24K

Holdings After Transaction: Common Stock — 132,650 shares (Indirect, See footnote)

Footnotes (5)

1. F1. Shares were sold pursuant to a Rule 10b5-1 trading plan on April 8, 2026.
2. F2. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $13.95 to $14.02 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
3. F3. These shares are held directly by Atlas Venture Fund XI, L.P. ("Atlas XI"). Atlas Venture Associates XI, L.P. ("AVA XI LP") is the general partner of Atlas XI. Atlas Venture Associates XI, LLC ("AVA XI LLC") is the general partner of AVA XI LP. The Reporting Person is a member of AVA XI LLC and disclaims Section 16 beneficial ownership of such shares, except to the extent of his pecuniary interest therein, if any.
4. F4. These shares are held directly by Atlas Venture Opportunity Fund II, L.P. ("AVOF II"). Atlas Venture Associates Opportunity II, L.P. ("AVAO II LP") is the general partner of AVOF II. Atlas Venture Associates Opportunity II, LLC ("AVAO II LLC") is the general partner of AVAO II LP. The Reporting Person is a member of AVAO II LLC and disclaims Section 16 beneficial ownership of such shares, except to the extent of his pecuniary interest therein, if any.
5. F5. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $13.95 to $14.59 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

Key Figures

Total shares sold: 48,690 shares Shares sold September 11, 2026: 8,450 shares; 1,750 shares Shares sold September 14, 2026: 31,888 shares; 6,602 shares +5 more

8 metrics

Total shares sold 48,690 shares Aggregate net shares sold across four transactions reported for September 11 and 14, 2026

Shares sold September 11, 2026 8,450 shares; 1,750 shares Two indirect sales at a weighted average price of $13.99 per share

Shares sold September 14, 2026 31,888 shares; 6,602 shares Two indirect sales at a weighted average price of $14.12 per share

Weighted average sale price (Sept. 11, 2026) $13.99 per share Common stock sales by entities associated with director Formela

Weighted average sale price (Sept. 14, 2026) $14.12 per share Common stock sales by entities associated with director Formela

Price range for Sept. 11 trades $13.95–$14.02 per share Multiple transactions aggregated into the reported weighted average price

Price range for Sept. 14 trades $13.95–$14.59 per share Multiple transactions aggregated into the reported weighted average price

Rule 10b5-1 trading plan date April 8, 2026 Date the trading plan covering these sales was entered into

Key Terms

Rule 10b5-1 trading plan, weighted average price, Section 16 beneficial ownership, pecuniary interest, +1 more

5 terms

Rule 10b5-1 trading plan regulatory

"Shares were sold pursuant to a Rule 10b5-1 trading plan on April 8, 2026"

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

weighted average price financial

"The price reported in Column 4 is a weighted average price"

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

Section 16 beneficial ownership regulatory

"disclaims Section 16 beneficial ownership of such shares"

pecuniary interest financial

"except to the extent of his pecuniary interest therein"

indirect ownership financial

"These shares are held directly by Atlas Venture Fund XI, L.P."

FAQ

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

What insider activity did Korro Bio (KRRO) disclose in this Form 4?

Korro Bio disclosed that entities associated with director Jean Francois Formela sold 48,690 shares of common stock on September 11 and 14, 2026, in open-market or private transactions at weighted average prices of about $14 per share, under a Rule 10b5-1 trading plan.

Who actually held and sold the KRRO shares reported for Jean Francois Formela?

The shares were held and sold indirectly through Atlas Venture Fund XI, L.P. and Atlas Venture Opportunity Fund II, L.P.. Their respective general partners are Atlas Venture Associates XI, L.P. and Atlas Venture Associates Opportunity II, L.P., whose general partners are Atlas Venture Associates XI, LLC and Atlas Venture Associates Opportunity II, LLC.

How many KRRO shares were sold in each transaction reported?

On September 11, 2026, two sales of 8,450 and 1,750 shares occurred at a weighted average price of $13.99. On September 14, 2026, two sales of 31,888 and 6,602 shares occurred at a weighted average price of $14.12.

Were the September 2026 KRRO insider sales made under a Rule 10b5-1 plan?

Yes. A footnote states that the shares were sold pursuant to a Rule 10b5-1 trading plan entered into on April 8, 2026. This indicates the trades were pre-arranged under that plan.

Does Jean Francois Formela claim full beneficial ownership of the KRRO shares sold?

No. Footnotes state that Formela, a member of the entities’ general partners, disclaims Section 16 beneficial ownership of the shares held by Atlas Venture Fund XI, L.P. and Atlas Venture Opportunity Fund II, L.P., except to the extent of his pecuniary interest, if any.

At what price range were the KRRO shares sold in these transactions?

For the September 11, 2026 trades, shares were sold in multiple transactions at prices ranging from $13.95 to $14.02. For the September 14, 2026 trades, shares were sold at prices ranging from $13.95 to $14.59, with reported weighted average prices of $13.99 and $14.12 respectively.

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

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Available on EDGAR 09/15/2026 - 04:16 PM Accepted by SEC EDGAR 09/15/2026 - 04:15 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^*

FORMELA JEAN FRANCOIS

(Last) (First) (Middle)

C/O KORRO BIO, INC.

60 FIRST STREET, 2ND FLOOR, SUITE 250

(Street)

CAMBRIDGE MASSACHUSETTS 02141

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Korro Bio, Inc. [ KRRO ]

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/11/2026

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

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

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

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	09/11/2026		S(1)		8,450	D	$13.99(2)	672,498	I	See footnote(3)
Common Stock	09/11/2026		S(1)		1,750	D	$13.99(2)	139,252	I	See footnote(4)
Common Stock	09/14/2026		S(1)		31,888	D	$14.12(5)	640,610	I	See footnote(3)
Common Stock	09/14/2026		S(1)		6,602	D	$14.12(5)	132,650	I	See footnote(4)

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

Explanation of Responses:

1. Shares were sold pursuant to a Rule 10b5-1 trading plan on April 8, 2026.

2. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $13.95 to $14.02 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

3. These shares are held directly by Atlas Venture Fund XI, L.P. ("Atlas XI"). Atlas Venture Associates XI, L.P. ("AVA XI LP") is the general partner of Atlas XI. Atlas Venture Associates XI, LLC ("AVA XI LLC") is the general partner of AVA XI LP. The Reporting Person is a member of AVA XI LLC and disclaims Section 16 beneficial ownership of such shares, except to the extent of his pecuniary interest therein, if any.

4. These shares are held directly by Atlas Venture Opportunity Fund II, L.P. ("AVOF II"). Atlas Venture Associates Opportunity II, L.P. ("AVAO II LP") is the general partner of AVOF II. Atlas Venture Associates Opportunity II, LLC ("AVAO II LLC") is the general partner of AVAO II LP. The Reporting Person is a member of AVAO II LLC and disclaims Section 16 beneficial ownership of such shares, except to the extent of his pecuniary interest therein, if any.

5. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $13.95 to $14.59 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

	/s/ Ommer Chohan, Attorney-in-fact	09/15/2026
	** 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.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)