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[SCHEDULE 13D/A] GeneDx Holdings Corp. Amended Major Shareholder Report

Filing Impact
(Moderate)
Filing Sentiment
(Neutral)
Form Type
SCHEDULE 13D/A

Rhea-AI Filing Summary

GeneDx Holdings Corp. major shareholders Eli Casdin and Keith Meister have filed Amendment No. 10 to their Schedule 13D, updating their ownership and derivative positions in the company’s Class A common stock.

Based on 29,688,027 Shares outstanding as of May 1, 2026, Keith Meister is reported to beneficially own 5,005,494 Shares, representing 16.7% of the class, primarily through investment funds advised by Corvex Management LP and interests in CMLS Holdings LLC. Eli Casdin is reported to beneficially own 3,599,671 Shares, or 12.0% of the class, through Casdin-affiliated funds, CMLS Holdings LLC, and equity awards tied to his board service.

The amendment also describes cash-settled swaps entered into by Casdin Partners Master Fund, LP with Morgan Stanley, providing economic long exposure equivalent to a notional 850,000 Shares in total. These swaps are cash-settled only, confer no voting or dispositive power over GeneDx securities, and are expressly disclaimed as beneficial ownership.

Positive

  • None.

Negative

  • None.

Insights

Amended 13D refines large holders’ stakes and adds swap exposure.

The amendment details how funds associated with Eli Casdin and Keith Meister collectively hold sizable positions in GeneDx Holdings Corp. Common stock ownership is broken down by entity, with beneficial ownership percentages calculated against 29,688,027 Shares outstanding as of May 1, 2026.

The filing also outlines three cash-settled swaps between Casdin Partners Master Fund, LP and Morgan Stanley referencing an aggregate notional 850,000 Shares, with cost bases between $38.1543 and $41.0261 per Share and termination dates in June 2029. These instruments provide economic exposure but no voting or dispositive rights, and beneficial ownership of the referenced Shares is expressly disclaimed.

Overall, this looks like a detailed position update rather than a transformative event. Future GeneDx filings may clarify any further changes in equity or derivative exposure if these holders adjust their strategies or unwind derivatives near their 2029 termination dates.

Shares outstanding 29,688,027 Shares Class A Shares outstanding as of May 1, 2026
Meister beneficial ownership 5,005,494 Shares (16.7%) Aggregate beneficial ownership of GeneDx Class A common stock
Casdin beneficial ownership 3,599,671 Shares (12.0%) Aggregate beneficial ownership of GeneDx Class A common stock
Casdin Partners Master Fund holdings 3,007,164 Shares (10.1%) Shares held by Casdin Partners Master Fund, LP
CMLS Holdings LLC holdings 537,285 Shares (1.8%) Shares beneficially owned via CMLS Holdings LLC
Swap notional exposure 50,000 / 300,000 / 500,000 Shares Three cash-settled swaps referencing GeneDx Shares
Swap cost bases $39.6602, $41.0261, $38.1543 per Share Cost basis for each cash-settled swap with Morgan Stanley
Warrant exercise price $379.50 per Share Exercise price of 204,141 private placement warrants
beneficial ownership financial
"Percent of class represented by amount in Row (11) 16.7 % ... beneficially owned"
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.
cash-settled swaps financial
"Casdin Partners Master Fund, LP entered into cash-settled swaps with Morgan Stanley"
margin accounts financial
"may effect purchases of securities through margin accounts maintained for investment funds"
A margin account is a brokerage account that lets an investor borrow money from the broker to buy more securities than they could with cash alone, using the securities in the account as security for the loan. Think of it like a mortgage for stock purchases: borrowing increases potential gains but also magnifies losses, can trigger a forced sale if the account falls below required limits, and carries interest costs—factors investors must manage carefully.
private placement warrants financial
"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
"20,517 Shares that were issued upon the 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.
notional interest financial
"economic long-side exposure comparable to a notional interest in 500,000 Shares"





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)
05/07/2026

(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).




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CMLS HOLDINGS LLC
Signature:/s/ Eli Casdin
Name/Title:Eli Casdin / Manager
Date:05/11/2026
C-LSH LLC
Signature:/s/ Eli Casdin
Name/Title:Eli Casdin / Managing Member
Date:05/11/2026
M-LSH LLC
Signature:/s/ Keith A. Meister
Name/Title:Keith A. Meister / Managing Member
Date:05/11/2026
Casdin Capital, LLC
Signature:/s/ Eli Casdin
Name/Title:Eli Casdin / Managing Member
Date:05/11/2026
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:05/11/2026
Casdin Partners GP, LLC
Signature:/s/ Eli Casdin
Name/Title:Eli Casdin / Managing Member
Date:05/11/2026
Eli Casdin
Signature:/s/ Eli Casdin
Name/Title:Eli Casdin / Self
Date:05/11/2026
Meister, Keith A.
Signature:/s/ Keith Meister
Name/Title:Keith Meister / Self
Date:05/11/2026
Corvex Management LP
Signature:/s/ Keith Meister
Name/Title:Keith Meister / Managing Partner
Date:05/11/2026

FAQ

What percentage of GeneDx (WGS) does Keith Meister beneficially own in this Schedule 13D/A?

Keith Meister is reported to beneficially own 5,005,494 GeneDx Shares, representing 16.7% of the outstanding Class A common stock. This figure includes Shares held by investment funds advised by Corvex Management LP and interests held through CMLS Holdings LLC, plus certain equity awards tied to board service.

How much GeneDx (WGS) stock does Eli Casdin beneficially own according to the amended 13D?

Eli Casdin is reported to beneficially own 3,599,671 GeneDx Shares, or 12.0% of the class. His position includes Shares and warrants held via CMLS Holdings LLC, holdings of Casdin Partners Master Fund, LP, and stock options and restricted stock units granted for his board service.

What outstanding share count is used to calculate ownership percentages in this GeneDx (WGS) Schedule 13D/A?

Ownership percentages are based on 29,688,027 GeneDx Class A Shares outstanding as of May 1, 2026. This outstanding share figure comes from GeneDx’s Form 10-Q filed on May 4, 2026, and is the denominator for all percentage-of-class calculations in the amended filing.

What cash-settled swaps linked to GeneDx (WGS) are disclosed for Casdin Partners Master Fund, LP?

Casdin Partners Master Fund, LP entered into three cash-settled swaps with Morgan Stanley referencing a notional 50,000, 300,000, and 500,000 Shares. They terminate in June 2029 with cost bases between $38.1543 and $41.0261 per Share, and settle entirely in cash.

Do the disclosed swaps give Casdin Partners Master Fund, LP voting power over GeneDx (WGS) shares?

No. The filing states the cash-settled swaps confer no direct or indirect voting, investment, or dispositive control over GeneDx securities. The counterparty is not required to acquire, hold, vote, or dispose of any GeneDx securities, and beneficial ownership of referenced Shares is expressly disclaimed.

What private placement warrants tied to GeneDx (WGS) are included in Casdin and Meister’s beneficial ownership?

Both Eli Casdin and Keith Meister’s beneficial ownership figures include 204,141 private placement warrants of GeneDx. Each warrant became exercisable on September 3, 2021 to purchase one Share at a price of $379.50 per Share, subject to adjustment, as described in GeneDx’s definitive proxy statement.