Casdin and Meister report 12% and 17.9% GeneDx (WGS) stakes

Q: How many GeneDx shares outstanding are used to calculate ownership in this 13D/A?

Ownership percentages are calculated using 29,688,027 Shares outstanding as of May 1, 2026. This share count comes from GeneDx’s Form 10-Q filed on May 4, 2026 and serves as the denominator for all reported beneficial ownership stakes.

Q: What GeneDx warrants are included in the Casdin and Meister ownership figures?

Both Eli Casdin and Keith Meister include 204,141 private placement warrants in their beneficial ownership. Each warrant became exercisable on September 3, 2021 to purchase one Share at an exercise price of $379.50 per Share , subject to adjustment under prior proxy terms.

Q: Do Casdin and Meister’s reported holdings include GeneDx board equity awards?

Yes. Eli Casdin’s sole beneficial ownership includes 11,882 Shares from vested options, 20,517 vested restricted stock units and 3,576 RSUs to vest. Keith Meister’s holdings include 11,207 Shares from vested options, 20,129 vested RSUs and 3,576 RSUs vesting within 60 days.

Q: How many GeneDx shares are reported by Casdin Partners Master Fund and Corvex Management?

Casdin Partners Master Fund, LP reports 3,007,164 Shares , representing 10.1% of GeneDx. Corvex Management LP reports 4,784,570 Shares , representing 16.1% of the class. These positions are part of the broader stakes attributed to Eli Casdin and Keith Meister, respectively.

Filing Impact

(Moderate)

Filing Sentiment

(Neutral)

Form Type

SCHEDULE 13D/A

Rhea-AI Filing Summary

GeneDx Holdings Corp. insiders Eli Casdin and Keith Meister report updated ownership positions in this Schedule 13D amendment. Based on 29,688,027 Shares outstanding as of May 1, 2026, Eli Casdin beneficially owns 3,599,671 Shares, representing 12% of the Class A common stock. Keith Meister beneficially owns 5,356,767 Shares, representing 17.9% of the class. These stakes include Shares held through entities such as CMLS Holdings LLC, Casdin Partners Master Fund, LP and investment funds advised by Corvex Management LP. Certain holdings include 204,141 private placement warrants exercisable at $379.50 per Share, fully vested options and restricted stock units granted for board service. The filing notes that recent trades by the reporting persons were executed as open market transactions.

Key Figures

Shares outstanding: 29,688,027 Shares Eli Casdin beneficial ownership: 3,599,671 Shares (12%) Keith Meister beneficial ownership: 5,356,767 Shares (17.9%) +5 more

8 metrics

Shares outstanding 29,688,027 Shares Class A common stock outstanding as of May 1, 2026

Eli Casdin beneficial ownership 3,599,671 Shares (12%) Beneficial ownership of GeneDx Class A common stock

Keith Meister beneficial ownership 5,356,767 Shares (17.9%) Beneficial ownership of GeneDx Class A common stock

Casdin Partners Master Fund stake 3,007,164 Shares (10.1%) Shares held of record by Casdin Partners Master Fund, LP

Corvex Management stake 4,784,570 Shares (16.1%) Shares beneficially owned by funds advised by Corvex Management LP

Private placement warrants 204,141 warrants at $379.50/share Warrants exercisable into Shares held via CMLS Holdings LLC

Casdin board equity awards 35,975 Shares total Includes options and RSUs tied to Eli Casdin’s board service

Meister board equity awards 34,912 Shares total Includes options and RSUs tied to Keith Meister’s board service

Key Terms

beneficial ownership, private placement warrants, restricted stock units, Schedule 13D, +2 more

6 terms

beneficial ownership financial

"The information set forth in the facing pages of this with respect to the sole and shared beneficial ownership and percentage of beneficial ownership of Shares"

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.

private placement warrants financial

"The Shares reflected as beneficially owned by Mr. Casdin include 333,144 Shares and 204,141 Shares issuable upon the exercise of 204,141 private placement warrants of the Issuer."

Private placement warrants are tradable coupons given directly to a limited group of investors that let the holder buy a company's shares at a fixed price before a set expiration date. They matter to investors because they can provide extra upside if the stock rises and give companies a way to raise money outside a public offering, but they also can increase the number of shares outstanding (dilution) and therefore affect share value and investor returns.

restricted stock units financial

"The Shares reflected as solely beneficially owned by Mr. Casdin also include 11,882 Shares issuable upon the exercise of fully vested options, 20,517 Shares that were issued upon the vesting of restricted stock units, and 3,576 Shares to be issued upon vesting of restricted stock units"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

Schedule 13D regulatory

"This Amendment No. 11 (the "Amendment") supplements the information set forth in the (the "") filed with the (the "SEC") on August 2, 2021, as amended"

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.

Form 10-Q regulatory

"References to percentage ownership of Shares in this Statement are based upon the 29,688,027 Shares stated to be outstanding as of May 1, 2026, in the Issuer's Form 10-Q filed with the SEC on May 4, 2026."

A Form 10-Q is a detailed report that publicly traded companies are required to file with regulators three times a year, providing an update on their financial health and business activities. It is important for investors because it offers timely insights into a company's performance, helping them make informed decisions about buying or selling stocks. Think of it as a regular check-up report that shows how well a company is doing.

open market transactions financial

"The transactions by the Reporting Persons in Shares since the previous amendment are set forth in Exhibit 99.1 … All such transactions were carried out in open market transactions."

Open market transactions are the buying and selling of a company’s shares or other securities conducted on public exchanges or through the wider market rather than through private deals or negotiated placements. They matter to investors because these trades change supply and demand in real time—like shoppers affecting a store’s inventory—and so can move prices, signal management or investor sentiment, affect liquidity, and alter ownership stakes that influence future returns and risk.

05/15/2026 - 07:05 PM

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 11)

GeneDx Holdings Corp.

(Name of Issuer)

Class A common stock, par value $0.0001 per share

(Title of Class of Securities)

81663L200

(CUSIP Number)

Eli Casdin and Keith Meister
c/o Corvex Management LP, 667 Madison Avenue
New York, NY, 10065
(212) 474-6700

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

05/14/2026

(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).

SCHEDULE 13D

Item 1.

Security and Issuer

(a)

Title of Class of Securities:

Class A common stock, par value $0.0001 per share

(b)

Name of Issuer:

GeneDx Holdings Corp.

(c)

Address of Issuer's Principal Executive Offices:

333 Ludlow Street, North Tower, 6th Floor, Stamford, CONNECTICUT , 06902.

Item 1 Comment:

This Amendment No. 11 (the "Amendment") supplements the information set forth in the Schedule 13D (the "Schedule 13D") filed with the United States Securities and Exchange Commission (the "SEC") on August 2, 2021, as amended as of January 19, 2022, May 3, 2022, December 5, 2022, February 1, 2023, April 20, 2023, November 17, 2023, May 31, 2024, May 7, 2025, August 26, 2025, and May 11, 2026 by CMLS Holdings LLC, Keith Meister, Eli Casdin and the other Reporting Persons named therein, relating to the shares of Class A common stock, par value $0.0001 per share ("Shares"), of GeneDx Holdings Corp. (formerly known as Sema4 Holdings Corp., the "Issuer"). Capitalized terms used but not defined herein shall have the meanings ascribed to them in the Schedule 13D, as amended. The information set forth in response to each separate Item below shall be deemed to be a response to all Items where such information is relevant. Item 3 to the Schedule 13D is supplementally amended as follows, and Item 5 to the Schedule 13D is amended and restated as follows. Information with respect to each Reporting Person is given solely by such Reporting Person and no Reporting Person assumes responsibility for the accuracy or completeness of the information furnished by another Reporting Person, except as otherwise provided in Rule 13d-1(k).

Item 3.

Source and Amount of Funds or Other Consideration

The information set forth in Item 5(c) is hereby incorporated by reference into this Item 3. Such Shares reported as purchased in Item 5(c) were purchased with the working capital of investment funds advised by Corvex Management LP.

Item 5.

Interest in Securities of the Issuer

(a)

The information set forth in the facing pages of this Schedule 13D with respect to the sole and shared beneficial ownership and percentage of beneficial ownership of Shares by the Reporting Persons is hereby incorporated by reference into this Item 5. The information in Item 5(b) below is hereby incorporated by reference into this Item 5(a). References to percentage ownership of Shares in this Statement are based upon the 29,688,027 Shares stated to be outstanding as of May 1, 2026, in the Issuer's Form 10-Q filed with the SEC on May 4, 2026. The filing of this Statement shall not be construed as an admission that a Reporting Person beneficially owns those Shares held by any other Reporting Person.

(b)

Eli Casdin has the sole power to vote or direct the vote and sole power to dispose or to direct the disposition of 35,975 Shares and shared power to vote or to direct the vote and shared power to dispose or to direct the disposition of 3,563,696 Shares. The Shares reflected as beneficially owned by Mr. Casdin include 333,144 Shares and 204,141 Shares issuable upon the exercise of 204,141 private placement warrants of the Issuer. On September 3, 2021, each private placement warrant became exercisable to purchase one Share at a price of $379.50 per share, subject to adjustment, as described in the definitive proxy statement of the Issuer (File No. 001-39482) filed with the SEC on July 2, 2021. CMLS Holdings LLC is the record holder of these Shares and warrants. The Board of Managers of CMLS Holdings LLC is comprised of Mr. Casdin and Mr. Meister who share voting and investment discretion with respect to the Shares held of record by CMLS Holdings LLC. C-LSH LLC and M-LSH LLC are the members of CMLS Holdings LLC, and Mr. Casdin is the managing member of C-LSH LLC. As such, each of the foregoing may be deemed to have or share beneficial ownership of the Shares held directly by CMLS Holdings LLC. Casdin Partners Master Fund, LP is the record holder of 3,007,164 Shares reported herein. Casdin Capital, LLC is the investment adviser to Casdin Partners Master Fund, LP and may be deemed to have or share beneficial ownership of the 3,007,164 Shares held by Casdin Partners Master Fund, LP. Casdin Partners GP, LLC is the general partner of Casdin Partners Master Fund LP and may be deemed to have or share beneficial ownership of the 3,007,164 Shares held by Casdin Partners Master Fund, LP, and Casdin Partners GP, LLC is also the direct beneficial owner of 19,247 Shares. Eli Casdin is the managing member of Casdin Capital, LLC and Casdin Partners GP, LLC. As such, each of the foregoing may be deemed to have or share beneficial ownership of the Shares held directly by Casdin Partners Master Fund, LP and Eli Casdin may be deemed the beneficial owner of the 19,247 Shares held by Casdin Partners GP, LLC. The Shares reflected as solely beneficially owned by Mr. Casdin also include 11,882 Shares issuable upon the exercise of fully vested options, 20,517 Shares that were issued upon the vesting of restricted stock units, and 3,576 Shares to be issued upon vesting of restricted stock units, in each case that were granted to Mr. Casdin in connection with his service on the board of directors of the Issuer. Keith Meister has the sole power to vote or to direct the vote and sole power to dispose or to direct the disposition of 4,819,482 Shares and shared power to vote or direct the vote and shared power to dispose or to direct the disposition of 537,285 Shares. The Shares reflected as beneficially owned by Mr. Meister include 333,144 Shares and 204,141 Shares issuable upon the exercise of 204,141 private placement warrants of the Issuer. On September 3, 2021, each private placement warrant became exercisable to purchase one Share at a price of $379.50 per share, subject to adjustment, as described in the definitive proxy statement of the Issuer (File No. 001-39482) filed with the SEC on July 2, 2021. CMLS Holdings LLC is the record holder of these Shares and warrants. The Board of Managers of CMLS Holdings LLC is comprised of Mr. Casdin and Mr. Meister who share voting and investment discretion with respect to the Shares held of record by CMLS Holdings LLC. C-LSH LLC and M-LSH LLC are the members of CMLS Holdings LLC, and Mr. Meister is the managing member of M-LSH LLC. As such, each of the foregoing may be deemed to have or share beneficial ownership of the Shares held directly by CMLS Holdings LLC. The Shares reflected as beneficially owned by Mr. Meister include 4,784,570 Shares owned by investment funds advised by Corvex Management LP, which may be deemed to be indirectly beneficially owned by Keith Meister by virtue of Mr. Meister's control of the general partner of Corvex Management LP. The Shares reflected as beneficially owned by Mr. Meister also include 11,207 Shares issuable upon the exercise of fully vested options, 20,129 Shares that were issued upon the vesting of restricted stock units, and 3,576 Shares to be issued upon vesting of restricted stock units within 60 days, in each case that were granted to Mr. Meister in connection with his service on the board of directors of the Issuer.

(c)

The transactions by the Reporting Persons in Shares since the previous Schedule 13D amendment are set forth in Exhibit 99.1 and such information is incorporated herein by reference. All such transactions were carried out in open market transactions.

(d)

No person other than the Reporting Persons is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares beneficially owned by the Reporting Persons.

(e)

Not applicable.

Item 7.

Material to be Filed as Exhibits.

Exhibit 99.1 Schedule of Transactions in Shares

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.

CMLS HOLDINGS LLC

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Manager
Date:	05/15/2026

C-LSH LLC

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member
Date:	05/15/2026

M-LSH LLC

Signature:	/s/ Keith A. Meister
Name/Title:	Keith A. Meister / Managing Member
Date:	05/15/2026

Casdin Capital, LLC

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member
Date:	05/15/2026

Casdin Partners Master Fund, L.P.

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member of Casdin Partners GP, LLC, its general partner
Date:	05/15/2026

Casdin Partners GP, LLC

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member
Date:	05/15/2026

Eli Casdin

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Self
Date:	05/15/2026

Meister, Keith A.

Signature:	/s/ Keith Meister
Name/Title:	Keith Meister / Self
Date:	05/15/2026

Corvex Management LP

Signature:	/s/ Keith Meister
Name/Title:	Keith Meister / Managing Partner
Date:	05/15/2026

Source: View Original Filing on SEC EDGAR

FAQ

What percentage of GeneDx (WGS) does Eli Casdin report owning in this Schedule 13D/A?

Eli Casdin reports beneficial ownership of 3,599,671 GeneDx Shares, equal to 12% of the Class A common stock. This includes direct holdings, shares and warrants through CMLS Holdings LLC, fund interests and equity awards tied to his board service.

What percentage of GeneDx (WGS) does Keith Meister report owning in this filing?

Keith Meister reports beneficial ownership of 5,356,767 GeneDx Shares, representing 17.9% of the Class A common stock. His position includes shares and warrants via CMLS Holdings LLC and 4,784,570 Shares owned by investment funds advised by Corvex Management LP.

How many GeneDx shares outstanding are used to calculate ownership in this 13D/A?

Ownership percentages are calculated using 29,688,027 Shares outstanding as of May 1, 2026. This share count comes from GeneDx’s Form 10-Q filed on May 4, 2026 and serves as the denominator for all reported beneficial ownership stakes.

What GeneDx warrants are included in the Casdin and Meister ownership figures?

Both Eli Casdin and Keith Meister include 204,141 private placement warrants in their beneficial ownership. Each warrant became exercisable on September 3, 2021 to purchase one Share at an exercise price of $379.50 per Share, subject to adjustment under prior proxy terms.

Do Casdin and Meister’s reported holdings include GeneDx board equity awards?

Yes. Eli Casdin’s sole beneficial ownership includes 11,882 Shares from vested options, 20,517 vested restricted stock units and 3,576 RSUs to vest. Keith Meister’s holdings include 11,207 Shares from vested options, 20,129 vested RSUs and 3,576 RSUs vesting within 60 days.

How many GeneDx shares are reported by Casdin Partners Master Fund and Corvex Management?

Casdin Partners Master Fund, LP reports 3,007,164 Shares, representing 10.1% of GeneDx. Corvex Management LP reports 4,784,570 Shares, representing 16.1% of the class. These positions are part of the broader stakes attributed to Eli Casdin and Keith Meister, respectively.