OpenAI’s Checkout Example Is Still API Version 2025-09-12

Updated November 10, 2026. Versions, commits, and headers below were read that day from GitHub, ucp.dev, OpenAI’s developer docs, and Google’s Canada post.

2025-09-12. That is the API-Version example on OpenAI’s Agentic Checkout spec. The page’s Last-Modified header was Tue, 10 Nov 2026 05:35:09 GMT. The date in the example is 424 days before November 10, 2026.

The Agentic Commerce Protocol repository does not use that string as its latest snapshot. Its README points the OpenAPI, the JSON Schema, and the examples at spec/2026-04-17. April 17, 2026 is 217 days after September 12, 2025, and 207 days before November 10, 2026.

A store that “implements ACP” has to say which of those two strings it means. Universal Commerce Protocol has a third date. Its latest release tag is v2026-08-25.

Which version should you code against?

Code against a release tag or a dated spec folder. A commit on main is not that folder.

The feed a shopping agent is allowed to quote is a separate file. The field list is How to make your store readable by AI shopping agents. Who can pay today is Can an AI shopping agent check out for you?. The six-company calendar through May 2027 is AI shopping agents, the next 6 months.

ACP’s repo stopped on July 18. OpenAI’s page did not.

At 13:39:46 GMT the ACP repository had 1,600 stars, 259 forks, and 148 open issues. GitHub’s open-issue count includes pull requests. pushed_at was 2026-07-18T04:51:51Z. The newest commit, 7fdd78df67, has that same timestamp and the message “SEP: Optional product URL on checkout Item (#281).” July 18 is 115 days before November 10.

The releases API returned an empty list. Versions live as directories. On main those directories are 2025-09-29, 2025-12-12, 2026-01-16, 2026-01-30, 2026-04-17, and unreleased. The README table calls spec/2026-04-17/openapi/ the latest stable OpenAPI. The status badge says beta. The license file is Apache-2.0.

changelog/unreleased holds 17 markdown files plus a .gitkeep. They have not been copied into a dated snapshot. One of the 17 is stale-pr-reminder.md, a process note. The directory is not a hidden 2026-11-10 release.

Two maintainer files do not list the same companies. The README badge says the spec is maintained by OpenAI and Stripe. MAINTAINERS.md lists three lead maintainers: OpenAI, Stripe, and Meta. The governance doc says the technical steering committee has up to seven seats, and that the founding maintainers’ veto is a last resort.

OpenAI’s own checkout page, touched the morning of November 10, still teaches the older example. The request-header table sets API-Version to 2025-09-12. The same page says: “In the future, the Agentic Checkout Spec will support MCP servers.” The GitHub README says the 2026-04-17 snapshot is the one that added cart, feed, orders, authentication, and MCP. If you are about to expose checkout as an MCP server, those two sentences cannot both be your spec.

Key concepts, Last-Modified 05:37:59 GMT, still describes Instant Checkout inside ChatGPT. It says the checkout session is rendered in the OpenAI UI, and that checkout state and payment processing stay on the merchant’s systems. The same page says OpenAI is not the merchant of record. Get Started, Last-Modified 05:00:52 GMT, says product-feed onboarding is available to approved partners and tells you to apply, then upload a feed over SFTP. The first step in that guide is the feed, not POST /checkout_sessions.

UCP’s release tag is August 25. Main moved this morning.

At 13:39:45 GMT Universal-Commerce-Protocol/ucp had 3,489 stars, 493 forks, and 263 open issues, the same open-issue field that includes pull requests. That is 2.18 times the ACP star count, a gap of 1,889. pushed_at was 2026-11-10T06:36:00Z. The license field was Apache-2.0.

The releases list has four tags. The newest is v2026-08-25, published 2026-08-25T13:53:03Z. Then v2026-04-08, v2026-01-23, and v2026-01-11.

The newest commit on main is 5f42601e42 at 2026-11-10T06:30:29Z: “feat: add purchase options extension and subscription policy (#890).” The two before it are a list-price field on November 9 and a checkout-docs clarification on November 7. The versioning guide says new development happens on main, and that a release branch named release/YYYY-MM-DD is cut when the Tech Council approves a version, then tagged. No v2026-11-10 tag was in the releases response.

The specification overview at ucp.dev carried Last-Modified Tue, 10 Nov 2026 06:36:34 GMT, six minutes after that commit. The profile example on the page still says "version": "2026-08-25". The docs site can move without the version string moving.

The Shopping Tech Council names 17 people. The companies on that table are Google (5), Shopify (4), and one seat each for Etsy, Meta, Amazon, Target, Microsoft, Stripe, Salesforce, and Wayfair. Amit Handa of Google is marked as a standing Governing Council member. A star count is not a seat count. ACP’s 1,600 stars do not mean fewer companies can implement it.

Google named UCP for Canada. It did not name a spec date.

Google’s November 4, 2026 Canada post says direct checkout, powered by UCP, is expanding to Canadian shoppers in AI Mode and the Gemini app. It names lululemon, select Shopify merchants, Shoppers Drug Mart, and Simons. It says retailers remain the seller of record. It says simplified UCP integration inside Merchant Center starts next year.

The post does not print 2026-08-25 or 2026-04-08. The Merchant Center guide, Last-Modified Thu, 29 Oct 2026 01:45:42 GMT, tells a merchant to set native_commerce checkout eligibility to true for a product that should be buyable, and to leave it empty or false for products the guide lists as ineligible. Subscriptions are in that ineligible list. The November 10 commit on UCP main is a subscription policy. The October 29 guide has not absorbed it. If you sell a subscription, the guide you can follow today still says leave checkout eligibility off.

What this means if you are implementing checkout

Ship the feed first. Both protocols are useless to an agent that does not have a price, a stock state, and a product URL. OpenAI’s Get Started guide puts the feed before checkout. Google’s Canada post is a checkout announcement for named retailers, and the self-serve Merchant Center path is “starting next year,” not this week.

If the channel is Google AI Mode in Canada, the protocol Google named is UCP, and the release tag to read is v2026-08-25. Ignore the 06:30 UTC commit until it is tagged. A purchase-options extension on main is a draft of the next snapshot, including the part that talks about subscriptions the Merchant Center guide still excludes.

If the channel is ChatGPT, match the document OpenAI will certify you against. On November 10 that published checkout page still showed API version 2025-09-12 and still described an embedded checkout, with the merchant charging on the merchant’s own systems. The GitHub snapshot a protocol engineer will open is 2026-04-17, and it is 217 days newer than the example. Write down which one your integration uses. An agent that sends API-Version: 2026-04-17 to a server built from the OpenAI example, or the reverse, is a broken agentic checkout, not a second protocol.

Stars do not break the tie. UCP had 3,489. ACP had 1,600. Neither number is a merchant count, and neither number is the version string in the header.