Agentic Commerce Protocol (ACP) vs Universal Commerce Protocol (UCP)

Agentic Commerce Protocol (ACP) 16

The last release is 2026-04-17, 199 days before this check, and the site changelog and Stripe's and OpenAI's ACP pages show nothing newer (0). No release or merged change in the 90 days from 4 August; the last merged change is a SEP on 17 July 2026 (0). Outside contributors opened pull requests up to #316 on 30 October, none merged, among them #296 (Idempotency-Key in the MCP binding) and #305 (a SECURITY.md). Open counts and reply times weren't re-read (github.com pages refused), so the 1 October figures of 85 open issues and 51 open pull requests stand, not re-read on 2 November (5 of 25). No official SDK; Stripe's shared payment token API is still a dated preview version, now 2026-09-30.preview (5 of 15). CI compiles schemas on every push and runs PR description and consistency checks, actions pinned to tags rather than commit SHAs (6 of 10). 0 + 0 + 5 + 5 + 6 = 16.

Universal Commerce Protocol (UCP) 70

The latest release is v2026-08-25, 73 days before this check (20). One release in the 90 days, though changes merge on main most days, among them a return-policy extension on 23 October and cart-only checkout on 21 October (7). Pull requests from Google, Shopify and outside contributors merge within days; 262 issues and pull requests are open (18). Official SDKs, updated 5 November (15). CI with linting, spellcheck, governance checks and example validation, and Dependabot updates (10). 20 + 7 + 18 + 15 + 10 = 70.

Agentic Commerce Protocol (ACP) 54

Protocol reading, split as reference implementations 30, live deployments 25, spec stability 25 and test vectors 20. OpenAI and Stripe run the two named implementations, but the repository holds no reference server or SDK, only specs and examples, and Stripe's agent side is still a preview, its shared payment token API on version 2026-09-30.preview under Stripe's agent services preview terms (20 of 30). On 2 November OpenAI's ACP docs cover product feeds over SFTP for approved partners and the Products and Promotions APIs, with no checkout pages. Stripe's Agentic Commerce Suite sells through agents "across multiple commerce protocols" in the US, Canada and select European countries, its own-checkout route is UCP, and its ACP page points at the 2026-04-17 spec. Stripe's overview and seller pages no longer name ACP, which on 1 October they gave beside UCP as a route to sell through. So the one live ACP use a founding implementer documents is OpenAI's feed onboarding, and no first-party page documents a live ACP checkout (10 of 25). Five dated versions between 29 September 2025 and 17 April 2026, two with breaking changes, each one deprecating the last, and the README still says beta (12 of 25). CI compiles every JSON Schema and checks examples against them on each push and pull request, with per-version example files, but there is no conformance suite, and issue #297 (the 2026-04-17 OpenAPI file rejecting six fields its JSON Schema declares) has no merged fix, since main hasn't changed since 17 July (12 of 20). 20 + 10 + 12 + 12 = 54.

Universal Commerce Protocol (UCP) 79

Protocol reading, split as reference implementations 30, live deployments 25, spec stability 25 and test vectors 20. Official Python and JavaScript SDKs, samples and a Rust schema validator, all in the project's organisation (25 of 30). Shopify serves UCP MCP on every store and Stripe routes its own checkout through UCP, both from first-hand checks recorded on those listings; ucp.dev lists about 50 endorsers, which are claims (20 of 25). Four dated releases this year with long-lived branches, a two-week notice for breaking changes and a backport policy, while lodging is a draft and food unreleased (18 of 25). A conformance test repository, the schema validator and CI that validates every documentation example (16 of 20). 25 + 20 + 18 + 16 = 79.

Agentic Commerce Protocol (ACP) 53

The payment credential is a delegated vault token bound to an allowance with max_amount, currency, checkout session, merchant and expires_at, and Stripe's shared payment tokens can be revoked by API at any time. Agent-to-seller auth is a plain Bearer token, and request signing with Signature and Timestamp is only a SHOULD (24 of 30). Each token is one-time within its allowance, 3DS and delegate authentication flows exist, and intervention_required hands control back to the buyer (16 of 20). Product data, descriptions and seller messages reach the agent as untrusted content, and we found no prompt-injection guidance in the RFCs or the site's security page (3 of 15). Order webhooks are signed with HMAC Merchant-Signature, Request-Id is echoed, and Stripe sends events when a token is used or deactivated (10 of 15). No SECURITY.md in the repository (an outside pull request adding one, #305 of 10 September, is unmerged), no security.txt on agenticcommerce.dev (404 on 2 November) and no disclosure route for the spec, and five design issues on signing, approval and idempotency (#291 to #295) were filed in public in August 2026 (0 of 20).

Universal Commerce Protocol (UCP) 67

OAuth 2.0 identity linking, RFC 9421 signatures for signed agents with key IDs bound to JWK thumbprints, and payment handlers with token exchange instead of raw card data (25 of 30). Checkout can hand back to the buyer through continue_url or an embedded checkout, and AP2 mandates record consent, but unattended completion is allowed by design (15 of 20). The permalink spec treats URL inputs as untrusted and requires server-side validation, but we found no guidance on product text reaching an agent (5 of 15). Order events go to business webhooks; we didn't read whether they are signed (8 of 15). SECURITY.md routes reports to Google's intake with a stated response time and GitHub advisories (14 of 20). 25 + 15 + 5 + 8 + 14 = 67.

Agentic Commerce Protocol (ACP) 77

Protocol reading. The MCP binding maps checkout to five tools (create, get, update, complete, cancel), though session objects are large, with the checkout OpenAPI file at 3,365 lines (20 of 25). Little to page or filter in a checkout, and the Feed API lists products without documented paging (10 of 20). Flat errors with type, code, message and param, messages entries on the session for out-of-stock and declined cases, and supported_versions on a version mismatch (20). Idempotency-Key is required on every POST, kept at least 24 hours, replays carry Idempotent-Replayed, and an in-flight duplicate gets 409 with Retry-After (20). No official SDK in the project; implementers write to the OpenAPI files or use Stripe's and OpenAI's own libraries, and every request needs an API-Version header (7 of 15).

Universal Commerce Protocol (UCP) 82

Protocol reading. Capability negotiation means an agent sees only what both sides support, though the schemas are large (18 of 25). Catalogue search pages with a cursor and has_next_page (15 of 20). An error model with codes and continue_url to hand a buyer to the business when the agent can't finish (18). The MCP binding requires an idempotency-key UUID on checkout calls for retry safety (18). Official SDKs in Python and JavaScript; every request needs a UCP-Agent profile (13 of 15). 18 + 15 + 18 + 18 + 13 = 82.

Agentic Commerce Protocol (ACP) 52

Apache-2.0 with a CLA, all specs public (30). agenticcommerce.dev has no privacy policy or terms; the RFCs require that logs never hold a full PAN or CVC and leave data handling to implementers (10 of 30). Each release marks the previous version deprecated in a dated changelog, but no notice period or end-of-support date is stated (12 of 20). A spec with no runtime of its own, so nothing to disclose about telemetry; the site names no subprocessors (10 of 20).

Universal Commerce Protocol (UCP) 47

Apache-2.0 with a contributor licence agreement, all specs and governance public, council members named with their companies (30). ucp.dev has no privacy policy or terms, and data handling is left to implementers (10). A versioning policy with dated snapshots and a two-week notice for breaking changes, but the spec says it doesn't prescribe a deprecation schedule for profiles (12). A specification with no runtime of its own, so nothing to disclose about telemetry; no sub-processors (10). 30 + 10 + 12 + 10 = 62.