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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934

Date of report (Date of earliest event reported): October 22, 2025

ARMATA PHARMACEUTICALS, INC.

(Exact name of Registrant as specified in its charter)

Washington |  | 001-37544 |  | 91-1549568
(State or other jurisdiction of incorporation or organization) |  | (Commission File Number) |  | (IRS Employer Identification No.)

| 5005 McConnell Avenue Los Angeles, California |  | 90066
| (Address of principal executive offices) |  | (Zip Code)

(310) 655-2928

(Registrant’s Telephone number)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the Registrant under any of the following provisions (see General Instruction A.2. below):

¨ | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Securities registered pursuant to Section 12(b) of the Act:

Title of Each Class |  | Trading Symbol(s) |  | Name of Each Exchange on Which Registered
Common Stock |  | ARMP |  | NYSE American

Item 7.01 | Regulation FD Disclosure.

On October 22, 2025, Armata Pharmaceuticals, Inc. (the “Company”) issued a press release announcing the presentation of positive results from its recently completed Phase 2a diSArm study of AP-SA02 as a potential treatment for complicated Staphylococcus aureus bacteremia at IDWeek 2025TM. The full text of the press release issued in connection with this announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

The Company posted to its website a copy of the late-breaking oral presentation delivered on October 22, 2025 by Dr. Loren G. Miller, M.D., M.P.H., at IDWeek 2025TM (the “IDWeek Presentation”). The IDWeek Presentation is furnished as Exhibit 99.2 to this Current Report on Form 8-K.

The information contained in the IDWeek Presentation is summary information that is intended to be considered in the context of the Company’s Securities and Exchange Commission (“SEC”) filings and other public announcements that the Company may make, by press release or otherwise, from time to time. The Company undertakes no duty or obligation to publicly update or revise the information contained in this report, except as may be required by the federal securities laws, although it may do so from time to time as its management believes is warranted. Any such updating may be made through the filing of other reports or documents with the SEC, through press releases or through other public disclosure. In addition, the Company disclaims any inferences regarding the materiality of such information that may arise as a result of it furnishing such information under Item 7.01 of this Current Report on Form 8-K.

The information in this Item 7.01 and the attached Exhibits 99.1 and 99.2 is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section. The information in this Item 7.01 and the attached Exhibits 99.1 and 99.2 shall not be incorporated by reference into any registration statement or other document pursuant to the Securities Act of 1933, as amended.

Item 9.01 | Financial Statements and Exhibits.

(d) Exhibits.

Exhibit No. |  | Description
99.1 |  | Press Release, dated October 22, 2025.
99.2 |  | IDWeek Presentation, dated October 22, 2025.
104 |  | Cover Page Interactive Data File (embedded within Inline XBRL document).

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: October 22, 2025 | Armata Pharmaceuticals, Inc.
| By: | /s/ Deborah L. Birx
| Name: | Deborah L. Birx, M.D.
| Title: | Chief Executive Officer (Principal Executive Officer)

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