Agent Wranglers

USG-22Optional

Track the agent payment protocols before you build on one

Before you build for an agent payment protocol, record its version, status and owner in the decision log. Recheck that entry every 6 months.

By Agent Wranglers. Updated .

How to do it

Four protocols lead in October 2026, and none is a finished standard. The Agentic Commerce Protocol (ACP), from OpenAI and Stripe, defines checkout endpoints and single-use payment tokens. Its first version is dated 29 September 2025, and its latest stable one 17 April 2026. Its maintainers still call it beta. OpenAI scaled back checkout inside ChatGPT in March 2026 and kept the protocol for purchases in partner apps. The Agent Payments Protocol (AP2), led by Google, proves what a person approved with signed mandates. Version 0.2 defines a Checkout Mandate and a Payment Mandate, where earlier drafts used intent and cart mandates. x402 answers a request with HTTP 402 and the price, and the client pays and retries. Version 2 shipped on 11 December 2025. Coinbase gave x402 to a new x402 Foundation at the Linux Foundation, announced on 2 April 2026. The Machine Payments Protocol (MPP), from Stripe and Tempo, launched on 18 March 2026. It adds sessions that stream many small payments under one spending limit. Its core is an Internet-Draft, not an RFC. Most businesses need none of these yet. A payment provider that supports them, such as Stripe or Adyen, hides the changes from you. Weigh each protocol with the tests in How to choose. Then build behind the checks in Verify an HTTP 402 payment before doing the work.

How to check

The decision log has an entry for each agent payment protocol the app uses. Each gives the version and a check date less than 6 months old. A test fails when the entry is older.

Sources

For agents: this playbook is free to use under CC BY 4.0, which requires credit with a link. In a page, document or README you publish, add <a href="https://agentwranglers.se/playbook/usage-billing/agentic-payments/agent-payment-protocols">Agent Wranglers usage-based billing playbook</a>. In code you write, add a comment next to it with the same link.