0001701108 2026-08-28 2026-08-28 0001701108 1 2026-08-28 2026-08-28 0001701108 2 2026-08-28 2026-08-28 0001701108 3 2026-08-28 2026-08-28 0001701108 4 2026-08-28 2026-08-28 0001701108 5 2026-08-28 2026-08-28 0001701108 6 2026-08-28 2026-08-28 0001701108 7 2026-08-28 2026-08-28 0001701108 8 2026-08-28 2026-08-28 0001701108 1 2026-08-28 2026-08-28 0001701108 2 2026-08-28 2026-08-28 0001701108 3 2026-08-28 2026-08-28 0001701108 4 2026-08-28 2026-08-28 iso4217:USD pure S-3 S-3 EX-FILING FEES 0001701108 Spero Therapeutics, Inc. N/A 0.0001381 0.0001381 0.0001381 0.0001381 0.0001381 0.0001381 0.0001381 true true false false S-3 Spero Therapeutics, Inc. Debt Debt Securities true Equity Common Stock, $0.001 par value per share true Equity Preferred Stock, $0.001 par value per share true Other Depositary Shares true Other Subscription Rights true Other Units true Other Warrants true false Unallocated (Universal) Shelf true 300000000.00 0.0001381 41430.00 300000000.00 41430.00 0.00 33445.90 7984.10 (a) Pursuant to Instruction 2.A(iii)(b) of Item 16(b) of Form S-3, this information is not required to be included. An indeterminate amount of the securities of each identified class is being registered as may from time to time be offered under this registration statement at indeterminate prices, along with an indeterminate number of securities that may be issued upon exercise, settlement, exchange or conversion of securities offered or sold under this registration statement, as shall have an aggregate offering price up to $300,000,000. Pursuant to Rule 416 under the Securities Act of 1933, as amended (the "Securities Act"), this registration statement also covers any additional securities that may be offered or issued in connection with any stock split, stock dividend or pursuant to anti-dilution provisions of any of the securities. Separate consideration may or may not be received for securities that are issuable upon conversion, exercise or exchange of other securities. In addition, the total amount to be registered and the proposed maximum aggregate offering price are estimated solely for the purpose of calculating the registration fee pursuant to Rule 457(o) under the Securities Act. (b) Each depositary share will be issued under a deposit agreement, will represent an interest in a fractional share or multiple shares of preferred stock and will be evidenced by a depositary receipt. (c) The subscription rights to purchase shares of common stock or preferred stock or other securities will be offered without additional consideration. (d) Units may be issued under a unit agreement and will represent an interest in one or more securities registered under this registration statement including shares of common stock or preferred stock, debt securities or warrants, in any combination, which may or may not be separable from one another. true Spero Therapeutics, Inc. S-3 333-277998 2024-03-15 2744.55 Unallocated (Universal) Shelf Unallocated (Universal) Shelf 300000000.00 true Spero Therapeutics, Inc. S-3 333-254170 2021-03-11 30701.35 Unallocated (Universal) Shelf Unallocated (Universal) Shelf 281405543.00 true Spero Therapeutics, Inc. S-3 333-277998 2024-03-15 2744.55 true Spero Therapeutics, Inc. S-3 333-254170 2021-03-11 32730.00 Pursuant to Rule 457(p) under the Securities Act, the registration fee applicable to the $300,000,000 of securities of the registrant being registered hereby in the amount of $41,430.00 is offset by $33,445.90, which represents the aggregate registration fee previously paid with respect to (a) $300,000,000 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-277998), which was filed with the Securities and Exchange Commission on March 15, 2024 and declared effective by the Commission on March 22, 2024, and (b) $281,405,543 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-254170), which was filed with the Commission on March 11, 2021 and declared effective by the Commission on March 29, 2021. All offerings of the unsold securities associated with the claimed fee offset pursuant to Rule 457(p) have been completed or terminated. Pursuant to Rule 457(p) under the Securities Act, the registration fee applicable to the $300,000,000 of securities of the registrant being registered hereby in the amount of $41,430.00 is offset by $33,445.90, which represents the aggregate registration fee previously paid with respect to (a) $300,000,000 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-277998), which was filed with the Securities and Exchange Commission on March 15, 2024 and declared effective by the Commission on March 22, 2024, and (b) $281,405,543 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-254170), which was filed with the Commission on March 11, 2021 and declared effective by the Commission on March 29, 2021. All offerings of the unsold securities associated with the claimed fee offset pursuant to Rule 457(p) have been completed or terminated. Pursuant to Rule 457(p) under the Securities Act, the registration fee applicable to the $300,000,000 of securities of the registrant being registered hereby in the amount of $41,430.00 is offset by $33,445.90, which represents the aggregate registration fee previously paid with respect to (a) $300,000,000 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-277998), which was filed with the Securities and Exchange Commission on March 15, 2024 and declared effective by the Commission on March 22, 2024, and (b) $281,405,543 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-254170), which was filed with the Commission on March 11, 2021 and declared effective by the Commission on March 29, 2021. All offerings of the unsold securities associated with the claimed fee offset pursuant to Rule 457(p) have been completed or terminated. Pursuant to Rule 457(p) under the Securities Act, the registration fee applicable to the $300,000,000 of securities of the registrant being registered hereby in the amount of $41,430.00 is offset by $33,445.90, which represents the aggregate registration fee previously paid with respect to (a) $300,000,000 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-277998), which was filed with the Securities and Exchange Commission on March 15, 2024 and declared effective by the Commission on March 22, 2024, and (b) $281,405,543 of unsold securities under the registrant's Registration Statement on Form S-3 (File No. 333-254170), which was filed with the Commission on March 11, 2021 and declared effective by the Commission on March 29, 2021. All offerings of the unsold securities associated with the claimed fee offset pursuant to Rule 457(p) have been completed or terminated.