Fairmount Funds Management LLC - 06 Oct 2025 Form 4 Insider Report for Jade Biosciences, Inc. (JBIO)

Reporting relationship: Director, 10%+ Owner
Issuer ticker: JBIO
Reported as of: 06 Oct 2025
Net transaction value: +$19,999,816
SEC form: 4
Accepted by SEC: 08 Oct 2025, 16:15:17 UTC
Prior SEC filing: 19 Sep 2025
Next SEC filing: 09 Oct 2025
Source filing: View source filing
Reporting owner signature: /s/ Tomas Kiselak, Managing Member of Fairmount Funds Management LLC

Key filing fact

Fairmount Funds Management LLC filed Form 4 for Jade Biosciences, Inc. (JBIO) on 08 Oct 2025.

Key facts

This page summarizes Fairmount Funds Management LLC's Form 4 filing for Jade Biosciences, Inc. (JBIO).
2 reported transactions and 1 derivative row are listed below.
Accepted by SEC: 08 Oct 2025, 16:15.

Change

Previous filing in this sequence was filed on 19 Sep 2025.
Current net transaction value: +$19,999,816.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (5)

CIK 0001802528 Primary reporting owner

Fairmount Funds Management LLC

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak, Managing Member of Fairmount Funds Management LLC
Signature date: 08 Oct 2025

CIK 0001769651

Fairmount Healthcare Fund II L.P.

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Fund II, L.P.
Signature date: 08 Oct 2025

CIK 0002042283

Fairmount Healthcare Co-Invest IV L.P.

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Co-Invest IV, L.P.
Signature date: 08 Oct 2025

CIK 0001830177

Kiselak Tomas

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak
Signature date: 08 Oct 2025

CIK 0001663607

Harwin Peter Evan

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Peter Harwin
Signature date: 08 Oct 2025

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

JBIO transaction

Common Stock

Award

Transaction value: $12,184,772
Shares: +1,333,126
Change %: +236%
Price: $9.14
Shares after: 1,897,677
Date: 06 Oct 2025
Ownership: By Fairmount Healthcare Fund II L.P.
Footnotes: F1, F2

JBIO holding

Common Stock

No transaction description listed

Transaction value
Shares
Change %
Price
Shares after: 2,655,817
Date: 06 Oct 2025
Ownership: By Fairmount Healthcare Co-Invest IV L.P.
Footnotes: F2

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

JBIO transaction Derivative

Pre-Funded Warrant (Right to Buy)

Award

Transaction value: $7,815,044
Shares: +855,047
Change %
Price: $9.14
Shares after: 855,047
Date: 06 Oct 2025
Ownership: By Fairmount Healthcare Fund II L.P.
Underlying class: Common Stock
Underlying amount: 855,047
Exercise price: $0.000100
Footnotes: F1, F2, F3

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Explanation of responses 3 footnotes

Footnote F1

The shares of Common Stock and Pre-Funded Warrants were purchased from the Issuer in a private placement, which transaction is exempt from Section 16(b) in accordance with Rule 16b-3(d)(1) promulgated under the Securities Exchange Act of 1934, as amended.

Footnote F2

Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II L.P. and Fairmount Healthcare Co-Invest IV L.P. The managers of Fairmount are Peter Harwin and Tomas Kiselak. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

Footnote F3

The Pre-Funded Warrants have no expiration date and are exercisable at any time after the date of issuance. A holder of Pre-Funded Warrants may not exercise the Pre-Funded Warrant if the holder, together with its affiliates, would beneficially own more than 9.99% of the number of outstanding shares of common stock of the Issuer immediately after giving effect to such exercise.

SEC remarks

Fairmount may be deemed a director by deputization of Issuer by virtue of the fact that Tomas Kiselak serves on the board of directors of the Issuer and is also a Managing Member of Fairmount.