X0202 SCHEDULE 13G 0001425738 XXXXXXXX LIVE Common Stock, $0.0001 par value per share 09/21/2026 0002088082 Electra Therapeutics, Inc. 284825106 230 E. Grand Avenue Suite S-100 South San Francisco CA 94080 Rule 13d-1(c) Redmile Group, LLC DE 0.00 5462881.00 0.00 5462881.00 5462881.00 N 8.7 IA OO The information in Item 4 relating to the shares of common stock, $0.0001 par value per share, of the Issuer (the "Common Stock") that are or may be deemed beneficially owned by Redmile Group, LLC and the calculation of the percent of such class of securities is incorporated by reference herein. Jeremy C. Green X0 0.00 5462881.00 0.00 5462881.00 5462881.00 N 8.7 HC IN The information in Item 4 relating to the shares of Common Stock that are or may be deemed beneficially owned by Jeremy Green and the calculation of the percent of such class of securities is incorporated by reference herein. Redmile Biopharma Investments II, L.P. DE 0.00 4796215.00 0.00 4796215.00 4796215.00 N 7.6 PN The information in Item 4 relating to the shares of Common Stock that are or may be deemed beneficially owned by Redmile Biopharma Investments II, L.P. and the calculation of the percent of such class of securities is incorporated by reference herein. Electra Therapeutics, Inc. 230 E. Grand Avenue Suite S-100 South San Francisco, CA 94080 Redmile Group, LLC Jeremy C. Green Redmile Biopharma Investments II, L.P. Redmile Group, LLC 900 Larkspur Landing Circle, Suite 270 Larkspur, California 94939 Jeremy C. Green c/o Redmile Group, LLC (NY Office) 45 W. 27th Street, Floor 11 New York, NY 10001 Redmile Biopharma Investments II, L.P. c/o Redmile Group, LLC 900 Larkspur Landing Circle, Suite 270 Larkspur, California 94939 Redmile Group, LLC: Delaware Jeremy C. Green: United Kingdom Redmile Biopharma Investments II, L.P.: Delaware Y Redmile Group, LLC - 5,462,881 (1) Jeremy C. Green - 5,462,881 (1) Redmile Biopharma Investments II, L.P. - 4,796,215 (2) Redmile Group, LLC - 8.7% (3) Jeremy C. Green - 8.7% (3) Redmile Biopharma Investments II, L.P. - 7.6% (3) Redmile Group, LLC - 0 Jeremy C. Green - 0 Redmile Biopharma Investments II, L.P. - 0 Redmile Group, LLC - 5,462,881 (1) Jeremy C. Green - 5,462,881 (1) Redmile Biopharma Investments II, L.P. - 4,796,215 (2) Redmile Group, LLC - 0 Jeremy C. Green - 0 Redmile Biopharma Investments II, L.P. - 0 Redmile Group, LLC - 5,462,881 (1) Jeremy C. Green - 5,462,881 (1) Redmile Biopharma Investments II, L.P. - 4,796,215 (2) (1) All of such shares of Common Stock are directly owned by certain investment vehicles, including Redmile Biopharma Investments II, L.P. ("RBI II"), for which Redmile is the investment manager (the "Redmile Funds"). Redmile may be deemed to beneficially own these securities in its capacity as their investment manager with discretion to vote and dispose of all shares of Common Stock held by the Redmile Funds. Mr. Green also may be deemed to beneficially own these securities as the principal of Redmile. Redmile and Mr. Green each disclaims beneficial ownership of these securities, except to the extent of its or his pecuniary interest in such securities, if any. (2) All of such shares of Common Stock are directly owned RBI II. (3) Percentage based on 62,766,955 shares of Common Stock outstanding immediately after the initial public offering, as reported in the Issuer's Prospectus dated September 17, 2026 filed with the SEC on September 18, 2026. Y Y N See the response to Item 4. Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11. Exhibit 99.1 - Joint Filing Agreement Redmile Group, LLC /s/ Jeremy C. Green 09/28/2026 Jeremy C. Green /s/ Jeremy C. Green 09/28/2026 Redmile Biopharma Investments II, L.P. /s/ Jeremy C. Green 09/28/2026