Upstream Bio, Inc. 8-K

What Happened

• Upstream Bio, Inc. announced on March 26, 2026 that it entered into a Sales Agreement with Leerink Partners LLC to conduct an at-the-market (ATM) equity offering. Under the agreement, the company may offer and sell up to $150,000,000 of its common stock from time to time through or to the Agent.
• The offering is being made under the company’s shelf registration on Form S-3ASR (File No. 333-291267) that was filed November 5, 2025 and is supported by a prospectus supplement filed March 26, 2026. Goodwin Procter LLP provided a legal opinion on the validity of the shares.

Key Details

• Maximum aggregate amount: $150,000,000 of common stock.
• Sales agent: Leerink Partners LLC; commission up to 3.0% of gross proceeds per sale.
• Date filed: Sales Agreement and prospectus supplement filed March 26, 2026; shelf registration effective under Rule 462(e).
• Company and Agent may suspend or terminate the program; neither party is obligated to sell or procure specific amounts of shares.

Why It Matters

• This ATM gives Upstream Bio a flexible, on‑demand way to raise capital by selling shares into the market as needed, without a single large registered offering. That can help fund operations or programs without long lead times.
• For existing shareholders, any shares sold under the ATM will dilute ownership and could affect share supply and market price; investors should monitor future prospectus supplements and SEC filings for actual sales and changes in shares outstanding.
• Costs and mechanics matter: Leerink’s commission (up to 3.0%) will reduce net proceeds, and sales will occur subject to market conditions, Nasdaq rules and the mutual agreement between the company and the Agent.