Notice of Proposed Sale · 144

Korro Bio, Inc.

KRRONASDAQEQUITYCurrent

Notice of Proposed Sale

Filed Aug 26, 2026Accepted Aug 26, 2026, 5:23 PM EDTFiling CIK 1703647Accession 0001628280-26-059121

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Structured filing — 144

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Notice of proposed sale. The proposed amounts below do not establish that a sale occurred.

Proposed-sale notice

Issuer: Korro Bio, Inc.
Issuer CIK: 0001703647
SEC file number: 001-39062
Phone: 6174681999
Person for whose account securities are to be sold: Atlas Venture Opportunity Fund II, L.P.
Relationships to issuer: Shareholder
Street: 60 First Street
Street (continued): 2nd Floor, Suite 250
City: Cambridge
State / country code: MA
Postal code: 02141

Securities proposed for sale

Securities proposed for sale · 1 reported row
Security	Proposed units	Aggregate market value	Units outstanding	Approximate sale date	Exchange	Broker / market maker
Common Stock	51	700.23	14,725,646	08/26/2026	Nasdaq	Merrill Lynch

Broker / market maker — proposed row 1, entry 1

Name: Merrill Lynch
Street: 555 California Street
Street (continued): 18th Floor
City: San Francisco
State / country code: CA
Postal code: 94104

Acquisition of securities to be sold

Acquisition of securities to be sold · 1 reported row
Security	Acquired	Nature of acquisition	Acquired from	Amount acquired	Gift transaction	Payment date	Nature of payment
Common Stock	04/22/2024	Private Placement	Issuer	51	N	04/22/2024	Cash

Sales reported in the preceding three months

Sales reported in the preceding three months · 16 reported rows
Seller	Security	Sale date	Amount sold	Gross proceeds
Atlas Venture Fund XI, L.P.	Common Stock	05/28/2026	2,441	34,051.95
Atlas Venture Fund XI, L.P.	Common Stock	06/22/2026	3,382	47,178.9
Atlas Venture Fund XI, L.P.	Common Stock	06/23/2026	101,579	1,447,785.17
Atlas Venture Fund XI, L.P.	Common Stock	06/24/2026	41,345	603,694.88
Atlas Venture Fund XI, L.P.	Common Stock	07/02/2026	85,955	1,206,249.49
Atlas Venture Fund XI, L.P.	Common Stock	07/06/2026	817	11,405.24
Atlas Venture Fund XI, L.P.	Common Stock	08/11/2026	1,775	24,772.79
Atlas Venture Fund XI, L.P.	Common	08/19/2026	23,584	330,159.49
Atlas Venture Opportunity Fund II, L.P.	Common Stock	05/28/2026	419	5,845.05
Atlas Venture Opportunity Fund II, L.P.	Common Stock	06/22/2026	580	8,091
Atlas Venture Opportunity Fund II, L.P.	Common Stock	06/23/2026	17,426	248,369.29
Atlas Venture Opportunity Fund II, L.P.	Common Stock	06/24/2026	7,093	103,567.73
Atlas Venture Opportunity Fund II, L.P.	Common Stock	07/02/2026	14,745	206,923.96
Atlas Venture Opportunity Fund II, L.P.	Common Stock	07/06/2026	8,506	118,742.91
Atlas Venture Opportunity Fund II, L.P.	Common Stock	08/11/2026	368	5,135.99
Atlas Venture Opportunity Fund II, L.P.	Common Stock	08/19/2026	4,884	68,372.58

Seller — prior-sale row 1, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 2, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 3, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 4, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 5, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 6, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 7, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 8, entry 1

Name: Atlas Venture Fund XI, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 9, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 10, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 11, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 12, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 13, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 14, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 15, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Seller — prior-sale row 16, entry 1

Name: Atlas Venture Opportunity Fund II, L.P.
Street: 300 Technology Sq Ste 8
City: Cambridge
State / country code: MA
Postal code: 02139

Prior-sale reporting

Nothing to report for the preceding three months: N

Notice signature

Notice date: 08/26/2026
Signed: Ommer Chohan
Plan adoption dates: 04/08/2026

Company context

Korro is a clinical-stage biopharmaceutical company leveraging a novel oligonucleotide promoted editing of RNA (OPERA®) platform to develop a new class of genetic medicines for rare and highly prevalent diseases. OPERA provides precise, tissue-directed delivery of RNA-editing oligonucleotides (REOs) that modify the targeted native mRNA transcript to repair or form a de novo protein with enhanced functionality. The platform combines a suite of capabilities consisting of sophisticated knowledge of transcription biology through ADAR proteins (Adenosine Deaminases Acting on RNA), machine learning optimization of REOs, linker chemistry expertise, along with use of a highly targeted tissue-specific delivery methodology. As such, the OPERA platform has enabled Korro to generate and advance a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, providing precise yet transient single base edits to produce therapeutic proteins with augmented activity versus its endogenous counterpart. By editing RNA instead of DNA, Korro is expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an REO-based approach, Korro expects to bring its medicines to patients by leveraging its proprietary OPERA platform with precedented delivery modalities, including N-acetylgalactosamine (GalNAc) conjugated for delivery for subcutan

Current securities

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