PLAINS ALL AMERICAN PIPELINE LP

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 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) – May 20, 2026

Plains All American Pipeline, L.P.

(Exact name of registrant as specified in its charter)

333 Clay Street, Suite 1600, Houston, Texas 77002

(Address of principal executive offices) (Zip Code)

713-646-4100

(Registrant’s telephone number, including area code)

(Former name or former address, if changed since last report)

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:

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

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

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.  ¨

The 2026 annual meeting of common unitholders and Series A Convertible Preferred unitholders (collectively, the “Unitholders”) of Plains All American Pipeline, L.P. (“PAA” or the “Partnership”) was held on May 20, 2026. At the annual meeting, the Unitholders (other than Plains AAP, L.P.) considered and voted on how to instruct PAA to vote the Class C shares of Plains GP Holdings, L.P. (“PAGP”) that PAA owns at PAGP’s annual meeting with respect to the following matters, each of which is described in greater detail in PAA’s Proxy Statement dated April 10, 2026 (the “Proxy Statement”): (i) the election of four Class I directors to serve on the board of directors of PAA GP Holdings LLC until the 2029 annual meeting; (ii) the ratification of the appointment of PricewaterhouseCoopers LLP as PAGP’s and PAA’s independent registered public accounting firm for the fiscal year ending December 31, 2026; and (iii) the approval, on a non-binding advisory basis, of our 2025 named executive officer compensation.

Out of the 530,943,161 common units and Series A Preferred units entitled to vote on Items 1, 2 and 3, approximately 83.2%, or 441,976,013 units, were represented in person or by proxy at the PAA annual meeting. The voting results for each matter presented at the PAA annual meeting were as follows:

*With respect to Items 1, 2 and 3, PAA Unitholders (other than Plains AAP, L.P.) voted on a “pass-through” basis by instructing PAA how to vote the PAGP Class C shares that it owns on Items 1, 2 and 3 at the PAGP annual meeting.

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.