OrbiMed reports 13.9% Q32 Bio ownership and 45-day lock-up (QTTB)

Rhea-AI Filing Summary

OrbiMed Advisors LLC and related investment entities report beneficial ownership of 4,127,987 shares of Q32 Bio Inc. common stock, representing 13.9% of the outstanding class. The amendment reflects that their percentage stake fell by more than 1% because shares outstanding increased to 29,708,814.

Within this total, OrbiMed Private Investments VII, LP holds 3,502,987 shares (about 11.8% of the company), and OrbiMed Genesis Master Fund, L.P. holds 625,000 shares (about 2.1%). OrbiMed Advisors, as managing member or general partner of affiliated entities, may be deemed to share voting and investment power over these positions through its investment committees.

The investors state they may buy more or sell shares over time depending on Q32 Bio’s business and market conditions but do not outline specific corporate-change plans. OrbiMed funds OPI VII and Genesis, and director Diyong Xu, are also subject to a 45‑trading‑day lock-up after the final prospectus, restricting sales, transfers, and hedging transactions, after which shares can be sold subject to Rule 144 and other securities laws.

Key Figures

OrbiMed Advisors beneficial ownership: 4,127,987 Shares OrbiMed Advisors percent of class: 13.9 % OPI VII Shares held: 3,502,987 Shares +5 more

8 metrics

OrbiMed Advisors beneficial ownership 4,127,987 Shares Aggregate Q32 Bio Shares OrbiMed Advisors may be deemed to beneficially own

OrbiMed Advisors percent of class 13.9 % Percent of Q32 Bio common stock represented by 4,127,987 Shares

OPI VII Shares held 3,502,987 Shares Q32 Bio Shares held by OrbiMed Private Investments VII, LP

OPI VII percent of class 11.8 % Percent of Q32 Bio common stock held by OPI VII

Genesis Shares held 625,000 Shares Q32 Bio Shares held by OrbiMed Genesis Master Fund, L.P.

Genesis percent of class 2.1 % Percent of Q32 Bio common stock held by Genesis

Shares outstanding 29,708,814 Shares Q32 Bio common stock outstanding per Rule 424(b)(5) prospectus dated July 15, 2026

Lock-up period 45 trading days Duration after the final prospectus during which sales and hedging are restricted

Key Terms

Schedule 13D, beneficial ownership, lock-up agreement, Rule 13d-3, +1 more

5 terms

Schedule 13D regulatory

"Amendment No. 4 supplements and amends the Statement on Schedule 13D"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

beneficial ownership financial

"the beneficial ownership of the outstanding Shares that the Reporting Persons may be deemed"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

lock-up agreement regulatory

"Each of OPI VII, Genesis, and Xu entered into a lock-up agreement"

A lock-up agreement is a contract that prevents company insiders and early investors from selling their shares for a fixed period after a stock sale, often after an initial public offering. It matters to investors because it temporarily limits the number of shares that can hit the market, which can keep the share price steadier; when the lock-up ends, a sudden increase in available shares can create extra volatility, revealing insiders’ confidence or lack thereof.

Rule 13d-3 regulatory

"securities which may be deemed to be beneficially owned (as such term is used in Rule 13d-3"

Rule 13d-3 defines who is treated as the beneficial owner of a company’s shares for U.S. securities disclosure rules — essentially anyone who has the power to vote or direct how shares are voted, or the power to buy or sell them, even if they don’t hold the certificates. For investors this matters because crossing certain ownership thresholds triggers public filing and disclosure obligations and signals potential control or influence, much like having the keys to a car implies you can drive it even if it’s registered to someone else.

Rule 144 regulatory

"Shares will be eligible for sale in the public market, subject to any applicable limitations under Rule 144"

Rule 144 is a U.S. securities regulation that sets conditions under which restricted or insider-held shares can be legally resold to the public, such as required holding periods, availability of public information, limits on how much can be sold at once, and certain filing requirements. For investors it matters because it determines when previously locked-up shares can enter the market — like a release valve that can increase supply, affect share price, and signal insider intent.

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

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Available on EDGAR 07/20/2026 - 09:33 PM Accepted by SEC EDGAR 07/20/2026 - 09:32 PM Learn about SEC filing dates

FAQ

What percentage of Q32 Bio (QTTB) does OrbiMed currently beneficially own?

OrbiMed and its affiliates report beneficial ownership of 4,127,987 Q32 Bio shares, or 13.9% of the common stock. This reflects indirect control through OrbiMed-managed funds, based on 29,708,814 shares outstanding cited in the company’s July 15, 2026 prospectus.

How many Q32 Bio (QTTB) shares are held by OrbiMed’s OPI VII fund?

OrbiMed Private Investments VII, LP holds 3,502,987 Q32 Bio shares, representing approximately 11.8% of the outstanding common stock. OrbiMed Capital GP VII LLC is the general partner of this fund, and OrbiMed Advisors is the managing member sharing voting and investment power.

What triggered Amendment No. 4 to OrbiMed’s Schedule 13D for Q32 Bio (QTTB)?

Amendment No. 4 was filed because OrbiMed’s percentage beneficial ownership decreased by more than 1% due to an increase in Q32 Bio’s shares outstanding, not because of reported share sales. The amendment updates ownership percentages using the new 29,708,814-share base.

What lock-up restrictions affect OrbiMed’s Q32 Bio (QTTB) holdings?

OPI VII, Genesis, and director Diyong Xu entered a 45‑trading‑day lock-up starting from the final prospectus date. During this period they agree not to sell, transfer, lend, or hedge Q32 Bio shares, including through options, swaps, short sales, or other derivative arrangements.

How many Q32 Bio (QTTB) shares are outstanding according to OrbiMed’s filing?

The filing bases ownership percentages on 29,708,814 Q32 Bio shares outstanding, as stated in the company’s Rule 424(b)(5) prospectus filed on July 15, 2026. OrbiMed’s reported 13.9%, 11.8%, and 2.1% stakes are all calculated using this share count.

Does OrbiMed outline future plans for its Q32 Bio (QTTB) investment?

OrbiMed states it may increase or reduce its Q32 Bio position over time, via open-market or private transactions, depending on company performance and market conditions. It does not currently describe specific plans for mergers, asset sales, governance changes, or other corporate actions.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

Q32 Bio Inc.

(Name of Issuer)

COMMON STOCK

(Title of Class of Securities)

746964105

(CUSIP Number)

OrbiMed Advisors LLC
601 Lexington Avenue, 54th Floor,
New York, NY, 10022
(212) 739-6400

OrbiMed Capital GP VII LLC
601 Lexington Avenue, 54th Floor,
New York, NY, 10022
(212) 739-6400

OrbiMed Genesis GP LLC
601 Lexington Avenue, 54th Floor,
New York, NY, 10022
(212) 739-6400

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

07/16/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 746964105

1

Name of reporting person

ORBIMED ADVISORS LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 4,127,987.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 4,127,987.00

11

Aggregate amount beneficially owned by each reporting person

4,127,987.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

13.9 %

14

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13D

CUSIP Number(s): 746964105

1

Name of reporting person

ORBIMED CAPITAL GP VII LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,502,987.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,502,987.00

11

Aggregate amount beneficially owned by each reporting person

3,502,987.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

11.8 %

14

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13D

CUSIP Number(s): 746964105

1

Name of reporting person

OrbiMed Genesis GP LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 625,000.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 625,000.00

11

Aggregate amount beneficially owned by each reporting person

625,000.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

2.1 %

14

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: COMMON STOCK
(b)	Name of Issuer: Q32 Bio Inc.
(c)	Address of Issuer's Principal Executive Offices: 830 Winter Street, Waltham, MASSACHUSETTS , 02451.
Item 1 Comment: This Amendment No. 4 ("Amendment No. 4") to Schedule 13D supplements and amends the Statement on Schedule 13D of OrbiMed Advisors LLC ("OrbiMed Advisors"), OrbiMed Capital GP VII LLC ("OrbiMed GP") and OrbiMed Genesis GP LLC ("OrbiMed Genesis") (collectively, the "Reporting Persons") originally filed with the Securities and Exchange Commission (the "SEC") on March 28, 2024, as amended by Amendment No. 1 filed with the SEC on March 12, 2026, Amendment No. 2 filed with the SEC on May 6, 2026, and Amendment No. 3 filed with the SEC on June 1, 2026. This Amendment No. 4 is being filed to report that as a result of an increase in the number of Shares outstanding, the beneficial ownership of the outstanding Shares that the Reporting Persons may be deemed to beneficially own decreased by more than 1%.
Item 2.	Identity and Background
(a)	OrbiMed Advisors is a limited liability company organized under the laws of Delaware and a registered investment adviser under the Investment Advisers Act of 1940, as amended. OrbiMed GP is a limited liability company organized under the laws of Delaware. OrbiMed Genesis is a limited liability company organized under the laws of Delaware. Carl L. Gordon is a United States citizen. Sven H. Borho is a German and Swedish citizen. W. Carter Neild is a United States citizen. Geoffrey C. Hsu is a United States citizen. C. Scotland Stevens is a United States citizen. David P. Bonita is a United States citizen. Peter A. Thompson is a United States citizen. Matthew S. Rizzo is a United States citizen. Mona Ashiya is a United States citizen. Trey Block is a United States citizen.
(b)	601 Lexington Avenue, 54th Floor, New York, New York 10022.
(c)	OrbiMed Advisors is the managing member or general partner of certain entities as more particularly described in Item 6 below. OrbiMed GP is the general partner of a limited partnership as more particularly described in Item 6 below. OrbiMed Genesis is the general partner of a limited partnership as more particularly described in Item 6 below. Carl L. Gordon is a member of OrbiMed Advisors. Sven H. Borho is a member of OrbiMed Advisors. W. Carter Neild is a member of OrbiMed Advisors. Geoffrey C. Hsu is a member of OrbiMed Advisors. C. Scotland Stevens is a member of OrbiMed Advisors. David P. Bonita is a member of OrbiMed Advisors. Peter A. Thompson is a member of OrbiMed Advisors. Matthew S. Rizzo is a member of OrbiMed Advisors. Mona Ashiya is a member of OrbiMed Advisors. Trey Block is the Chief Financial Officer of OrbiMed Advisors.
(d)	Not applicable.
(e)	Not applicable.
(f)	Item 2(a) is incorporated herein by reference.
Item 3.	Source and Amount of Funds or Other Consideration
	Not applicable.
Item 4.	Purpose of Transaction
	The Reporting Persons from time to time intend to review their investment in the Issuer on the basis of various factors, including the Issuer's business, financial condition, results of operations and prospects, general economic and industry conditions, the securities markets in general and those for the Issuer's Shares in particular, as well as other developments and other investment opportunities. Based upon such review, the Reporting Persons will take such actions in the future as the Reporting Persons may deem appropriate in light of the circumstances existing from time to time. If the Reporting Persons believe that further investment in the Issuer is attractive, whether because of the market price of Shares or otherwise, they may acquire Shares or other securities of the Issuer either in the open market or in privately negotiated transactions. Similarly, depending on market and other factors, the Reporting Persons may determine to dispose of some or all of the Shares currently owned by the Reporting Persons or otherwise acquired by the Reporting Persons either in the open market or in privately negotiated transactions. Except as set forth in this Schedule 13D, the Reporting Persons have not formulated any plans or proposals which relate to or would result in: (a) the acquisition by any person of additional securities of the Issuer or the disposition of securities of the Issuer, (b) an extraordinary corporate transaction, such as a merger, reorganization or liquidation, involving the Issuer or any of its subsidiaries, (c) a sale or transfer of a material amount of the assets of the Issuer or any of its subsidiaries, (d) any change in the present Board of Directors or management of the Issuer, including any plans or proposals to change the number or term of directors or to fill any existing vacancies on the board, (e) any material change in the Issuer's capitalization or dividend policy of the Issuer, (f) any other material change in the Issuer's business or corporate structure, (g) any change in the Issuer's charter or bylaws or other instrument corresponding thereto or other action which may impede the acquisition of control of the Issuer by any person, (h) causing a class of the Issuer's securities to be deregistered or delisted from a national securities exchange or to cease to be authorized to be quoted in an inter-dealer quotation system of a registered national securities association, (i) a class of equity securities of the Issuer becoming eligible for termination of registration pursuant to Section 12(g)(4) of the Act or (j) any action similar to any of those enumerated above.
Item 5.	Interest in Securities of the Issuer
(a)	The following disclosure is based upon 29,708,814 outstanding Shares as set forth in the Issuer's Rule 424(b)(5) Prospectus filed with the SEC on July 15, 2026. As of the date of this filing, OrbiMed Private Investments VII, LP ("OPI VII"), a limited partnership organized under the laws of Delaware, holds 3,502,987 Shares constituting approximately 11.8% of the issued and outstanding Shares. OrbiMed GP is the general partner of OPI VII pursuant to the terms of the limited partnership agreement of OPI VII, and OrbiMed Advisors is the managing member of OrbiMed GP pursuant to the terms of the limited liability company agreement of OrbiMed GP. As a result, OrbiMed Advisors and OrbiMed GP share power to direct the vote and disposition of the Shares held by OPI VII and may be deemed directly or indirectly, including by reason of their mutual affiliation, to be the beneficial owners of the Shares held by OPI VII. OrbiMed Advisors exercises this investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the Shares held by OPI VII. In addition, OrbiMed Advisors and OrbiMed GP, pursuant to their authority under the limited partnership agreements of OPI VII, caused OPI VII to enter into the agreements referred to in Item 6 below. As of the date of this filing, OrbiMed Genesis Master Fund, L.P. ("Genesis"), a limited partnership organized under the laws of the Cayman Islands, holds 625,000 Shares constituting approximately 2.1% of the issued and outstanding Shares. OrbiMed Genesis is the general partner of Genesis, pursuant to the terms of the limited partnership agreement of Genesis, and OrbiMed Advisors is the managing member of OrbiMed Genesis, pursuant to the terms of the limited liability company agreement of OrbiMed Genesis. As a result, OrbiMed Advisors and OrbiMed Genesis share power to direct the vote and disposition of the Shares held by Genesis and may be deemed, directly or indirectly, including by reason of their mutual affiliation, to be the beneficial owners of the Shares held by Genesis. OrbiMed Advisors exercises this investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the Shares held by Genesis. In addition, OrbiMed Advisors and OrbiMed Genesis, pursuant to their authority under the limited partnership agreement of Genesis, caused Genesis to enter into the agreements referred to in Item 6 below.
(b)	Item 5(a) is incorporated by reference herein.
(c)	Not applicable.
(d)	Not applicable.
(e)	Not applicable.
Item 6.	Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer
	In addition to the relationships between the Reporting Persons described in Items 2 and 5 above, OrbiMed GP is the general partner of OPI VII pursuant to the terms of the limited partnership agreement of OPI VII. Pursuant to this agreement and relationship, OrbiMed GP has discretionary investment management authority with respect to the assets of OPI VII. Such authority includes the power to vote and otherwise dispose of securities held by OPI VII. The number of outstanding Shares of the Issuer attributable to OPI VII is 3,502,987. OrbiMed GP, pursuant to its authority under the limited partnership agreement of OPI VII, may be considered to hold indirectly 3,502,987 Shares. In addition to the relationships between the Reporting Persons described in Items 2 and 5 above, OrbiMed Genesis is the general partner of Genesis, pursuant to the terms of the limited partnership agreement of Genesis. Pursuant to this agreement and relationship, OrbiMed Genesis has discretionary investment management authority with respect to the assets of Genesis. Such authority includes the power to vote and otherwise dispose of securities held by Genesis. The number of outstanding Shares of the Issuer attributable to Genesis is 625,000 Shares. OrbiMed Genesis, pursuant to its authority under the limited partnership agreement of Genesis, may be considered to hold indirectly 625,000 Shares. OrbiMed Advisors is the managing member of OrbiMed GP and OrbiMed Genesis, pursuant to the terms of the limited liability company agreements of OrbiMed GP and OrbiMed Genesis. Pursuant to these agreements and relationships, OrbiMed Advisors and OrbiMed GP have discretionary investment management authority with respect to the assets of OPI VII. OrbiMed Advisors and OrbiMed Genesis have discretionary investment management authority with respect to the assets of Genesis. Such authority includes the power of OrbiMed GP to vote and otherwise dispose of securities held by OPI VII and the power of OrbiMed Genesis to vote and otherwise dispose of the securities held by Genesis. The number of outstanding Shares attributable to OPI VII is 3,502,987 Shares and the number of Shares attributed to Genesis is 625,000 Shares. OrbiMed Advisors, pursuant to its authority under the terms of the limited liability company agreements of OrbiMed GP and OrbiMed Genesis, may also be considered to hold indirectly 4,127,987 Shares. Diyong Xu ("Xu"), an employee of OrbiMed Advisors, is a member of the Board of Directors of the Issuer and, accordingly, OrbiMed Advisors and OrbiMed GP may have the ability to affect and influence control of the Issuer. From time to time, Xu may receive stock options or other awards of equity-based compensation pursuant to the Issuer's compensation arrangements for non-employee directors. Pursuant to an agreement with OrbiMed Advisors and OrbiMed GP, Xu is obligated to transfer any securities issued under any such stock options or other awards, or the economic benefit thereof, to OrbiMed Advisors and OrbiMed GP, which will in turn ensure that such securities or economic benefits are provided to OPI VII. Lock-Up Agreement Each of OPI VII, Genesis, and Xu entered into a lock-up agreement (the "Lock-Up Agreement") pursuant to which, among other things, OPI VII, Genesis, and Xu each agreed that they will not, during the period beginning on the date of the final prospectus and ending 45 trading days thereafter (the "Lock-Up Period"), directly or indirectly (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any Shares owned or hereafter acquired by OPI VII, Genesis, or Xu or with respect to which OPI VII, Genesis, or Xu has or hereafter acquires the power of disposition (including, without limitation, Shares or such other securities which may be deemed to be beneficially owned (as such term is used in Rule 13d-3 of the Act and securities which may be issued upon exercise of a stock option or warrant by OPI VII, Genesis, or Xu or any other securities so owned convertible into or exercisable or exchangeable for Shares (2) enter into any hedging, swap, loan or other arrangement (including, without limitation, any short sale or the purchase or sale of, or entry into, any put or call option, or combination thereof, forward or any other derivative transaction or instrument, however described or defined) that transfers to another, in whole or in part, directly or indirectly, any of the economic consequences of ownership of Shares, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Shares or such other securities, in cash or otherwise. After the Lock-Up Period expires, each of OPI VII's, Genesis', and Xu's Shares will be eligible for sale in the public market, subject to any applicable limitations under Rule 144 under the Securities Act, and other applicable U.S. securities laws. The foregoing description of the Lock-Up Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Lock-Up Agreement, which are filed as Exhibit 2 and incorporated herein by reference.
Item 7.	Material to be Filed as Exhibits.
	Exhibit Description 1. Joint Filing Agreement among OrbiMed Advisors LLC, OrbiMed Capital GP VII LLC, and OrbiMed Genesis GP LLC. 2. Form of Lock-Up Agreement (incorporated by reference to Exhibit A of Exhibit 1.1 to the Issuer's Current Report on Form 8-K (File No. 001-38433), filed with the SEC on July 15, 2026.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

ORBIMED ADVISORS LLC

Signature:	/s/ Carl L. Gordon
Name/Title:	Carl L. Gordon/Member
Date:	07/20/2026

ORBIMED CAPITAL GP VII LLC

Signature:	/s/ Carl L. Gordon
Name/Title:	Carl L. Gordon/Member of OrbiMed Advisors LLC
Date:	07/20/2026

OrbiMed Genesis GP LLC

Signature:	/s/ Carl L. Gordon
Name/Title:	Carl L. Gordon/Member of OrbiMed Advisors LLC
Date:	07/20/2026