Upstream Bio (UPB) Proxy filing summary

Voting matters and shareholder proposals

• Election of two class II directors to serve until the 2029 annual meeting, with nominees H. Edward Fleming, Jr., M.D. and Liam Ratcliffe, M.B.Ch.B., Ph.D.

• Ratification of PricewaterhouseCoopers LLP as independent registered public accounting firm for the fiscal year ending December 31, 2026.

• Proxies authorized to vote on other business that may arise during the meeting or any adjournment.

Board of directors and corporate governance

• Board recommends voting in favor of both director nominees and the auditor ratification.

• Directors elected will serve three-year terms, expiring at the 2029 annual meeting.

Audit committee and external auditor matters

• Proposal to ratify PricewaterhouseCoopers LLP as the external auditor for the 2026 fiscal year.