Exhibit 23.1
CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM
We hereby consent to the incorporation by reference in this Registration Statement on Form S-8 of Upstream Bio, Inc. of our report dated June 12, 2024, except for the effects of the stock split discussed in Note 18 to the consolidated financial statements, as to which the date is October 7, 2024, relating to the financial statements, which appears in Upstream Bio, Inc.’s Amendment No. 1 to the Registration Statement on Form S-1 (No. 333-282197).
/s/ PricewaterhouseCoopers LLP
Boston, Massachusetts
October 11, 2024
