Aaron Deykin - 02 Jan 2026 Form 4 Insider Report for Upstream Bio, Inc. (UPB)

Reporting relationship: Chief Medical Officer
Issuer ticker: UPB
Reported as of: 02 Jan 2026
Net transaction value: $0
SEC form: 4
Accepted by SEC: 06 Jan 2026, 17:15:09 UTC
Prior SEC filing: 07 Feb 2025
Next SEC filing: 17 Mar 2026
Source filing: View source filing
Reporting owner signature: /s/ Allison Ambrose, Attorney-in-Fact

Key filing fact

Aaron Deykin filed Form 4 for Upstream Bio, Inc. (UPB) on 06 Jan 2026.

Key facts

This page summarizes Aaron Deykin's Form 4 filing for Upstream Bio, Inc. (UPB).
2 reported transactions and 1 derivative row are listed below.
Accepted by SEC: 06 Jan 2026, 17:15.

Change

Previous filing in this sequence was filed on 07 Feb 2025.
Current net transaction value: $0.

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 (1)

CIK 0002031693 Primary reporting owner

Deykin Aaron

Relationship: Chief Medical Officer
Address: UPSTREAM BIO, INC., 890 WINTER STREET, SUITE 200, WALTHAM
Signature: /s/ Allison Ambrose, Attorney-in-Fact
Signature date: 06 Jan 2026

Reported non-derivative transactions

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

UPB transaction

Common Stock

Award

Transaction value: $0
Shares: +32,000
Change %: +2024%
Price: $0.000000
Shares after: 33,581
Date: 02 Jan 2026
Ownership: Direct
Footnotes: F1, F2

Reported derivative securities

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

UPB transaction Derivative

Stock Option (Right to Buy)

Award

Transaction value: $0
Shares: +96,000
Change %
Price: $0.000000
Shares after: 96,000
Date: 02 Jan 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 96,000
Exercise price: $27.07
Footnotes: 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

Represents restricted stock units ("RSUs") granted pursuant to the Issuer's 2024 Stock Option and Incentive Plan. Each RSU represents the contingent right to receive one share of the Issuer's Common Stock upon vesting. The RSUs shall vest in sixteen equal quarterly installments following January 1, 2026, subject to the Reporting Person's continued service on each such vesting date.

Footnote F2

Includes 1,581 shares of Common Stock previously acquired under the Issuer's 2024 Employee Stock Purchase Plan.

Footnote F3

The shares underlying this option shall vest in forty-eight equal monthly installments following January 1, 2026, subject to the Reporting Person's continued service on each such vesting date.