FMR LLC and Abigail P. Johnson filed Amendment No. 3 to a Schedule 13G with the SEC on November 5, 2026, disclosing beneficial ownership of common stock in Upstream Bio Inc as of October 30, 2026.

Key Highlights

  • Aggregate beneficial ownership: FMR LLC and Abigail P. Johnson each reported beneficial ownership of 3,793,955 shares of Upstream Bio Inc common stock.
  • Percent of class: The 3,793,955 shares represent 6.9% of Upstream Bio Inc's outstanding common stock, according to the filing.
  • Sole voting power (FMR LLC): FMR LLC reported sole voting power over 3,790,763 shares, with 0 shares subject to shared voting power.
  • Sole dispositive power: Both FMR LLC and Abigail P. Johnson each reported sole dispositive power over 3,793,955 shares, with no shared dispositive power.
  • Triggering event date: The date of the event requiring this filing was October 30, 2026.
  • No single outside interest above 5%: The filing states that no one other person's interest in Upstream Bio Inc common stock is more than five percent of the total outstanding common stock.

FMR LLC and Abigail P. Johnson Disclose Ownership Position in Upstream Bio Inc

According to the filing, FMR LLC, a Delaware-organized holding company located at 245 Summer Street, Boston, Massachusetts 02210, submitted Amendment No. 3 to Schedule 13G covering common stock of Upstream Bio Inc (CUSIP 91678A107). The issuer's principal executive offices are listed as 890 Winter Street, Suite 200, Waltham, MA 02451. The filing was signed on November 5, 2026 by Stephanie J. Brown, acting under a power of attorney on behalf of both FMR LLC and Abigail P. Johnson.

The filing reports that FMR LLC holds sole voting power over 3,790,763 shares and sole dispositive power over 3,793,955 shares, with no shared voting or dispositive power reported. Abigail P. Johnson, identified as a United States individual, is reported to hold 0 shares with sole voting power but 3,793,955 shares with sole dispositive power, also with no shared voting or dispositive power. Both reporting persons list aggregate beneficial ownership of 3,793,955 shares, equal to 6.9% of the class, as of October 30, 2026.

The filing further states, under Item 6, that "one or more other persons are known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the COMMON STOCK of UPSTREAM BIO INC," but that no single other person's interest exceeds five percent of the total outstanding common stock. The certification language in the filing states that the securities "were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer."

What Was Disclosed

FMR LLC and Abigail P. Johnson filed Amendment No. 3 to Schedule 13G disclosing aggregate beneficial ownership of 3,793,955 shares, or 6.9%, of Upstream Bio Inc common stock, with the triggering event dated October 30, 2026.