Upstream Bio Inc

Item 2. Unregistered Sales of Equity Securities and Use of Proceeds.

(a) Recent sales of unregistered equity securities

During the period between July 1, 2024 and September 30, 2024, we issued options to purchase an aggregate of 35,666 shares of our common stock to certain employees under our 2021 Stock Option and Grant Plan at a weighted-average exercise price of $10.62 per share. We deemed these issuances to be exempt from registration under the Securities Act of 1933, as amended (the “Securities Act”), either in reliance on Rule 701 of the Securities Act as sales and offers under compensatory benefit plans and contracts relating to compensation in compliance with Rule 701, or in reliance on Section 4(a)(2), as transactions by an issuer not involving a public offering. On October 11, 2024, we filed a registration statement on Form S-8 under the Securities Act to register all of the shares of our common stock subject to outstanding options and all shares of our common stock otherwise issuable pursuant to our equity compensation plans.

(b) Use of proceeds from initial public offering

On October 10, 2024, our Registration Statement on Form S-1 (No. 333-282197) for our initial public offering (“IPO”) was declared effective by the Securities and Exchange Commission (“SEC”), pursuant to which we issued and sold an aggregate of 17,250,000 shares of common stock (inclusive of 2,250,000 shares of common stock sold pursuant to the underwriters' full exercise of their option to purchase additional shares) at a public offering price of $17.00 per share, for aggregate net cash proceeds of approximately $268.7 million, after deducting $20.5 million in underwriting discounts and commissions, and approximately $4.0 million in other offering costs.

J.P. Morgan Securities LLC, TD Securities (USA) LLC, Piper Sandler & Co. and William Blair & Company, L.L.C. acted as joint book-running managers for the offering, which closed on October 15, 2024.

In connection with our IPO, no payments for such expenses were made directly or indirectly to (i) any of our officers or directors or their associates, (ii) any persons owning 10% or more of any class of our equity securities or (iii) any of our affiliates.

There has been no material change in the planned use of proceeds from our IPO as described in our final prospectus filed with the SEC pursuant to Rule 424(b)(4) under the Securities Act on October 11, 2024 (File No. 333-282197).

(c) Issuer repurchases of securities

None.