UCP vs ACP: what's the difference?
UCP and ACP are both open standards for letting AI agents buy from stores. UCP, from Google and partners, covers the wider shopping journey through a profile at /.well-known/ucp. ACP, from OpenAI and Stripe, focuses on the checkout handshake. ARC measures UCP adoption across thousands of stores; ACP is not yet measured.
One-line difference
UCP publishes a store profile and covers search, cart and checkout. ACP is the checkout handshake between an agent and a merchant.
Side by side
| UCP | ACP | |
|---|---|---|
| Backers | Google, with partners including Shopify | OpenAI and Stripe |
| Scope | Profile, catalog, cart, checkout | Checkout handshake |
| Discovery | /.well-known/ucp on the store | No public file ARC can fetch |
| Licence | Published openly at ucp.dev | Apache 2.0 |
| ARC adoption | 1,522 of 4,318 (35.2%) transacts | Not measured |
Measured on the UCP cell. Not measured on ACP. Not measured is not zero.
What ARC can measure for each
ARC saved checks, accessed 2026-10-13
Declared: 1,896 of 4,318 (43.9%)Measured/.well-known/ucp answered HTTP 200 with a body
Valid: 1,862 of 4,318 (43.1%)MeasuredProfile passed ARC's validation
Usable: 1,717 of 4,318 (39.8%)MeasuredThe UCP catalog tool returned the tested product
Transacts: 1,522 of 4,318 (35.2%)MeasuredUCP create_cart returned a checkout link
ARC saved checks, accessed 2026-10-13
Declared: Not measuredNot measuredNo public discovery marker to check
Valid: Not measuredNot measuredNot checked
Usable: Not measuredNot measuredNot checked
Transacts: Not measuredNot measuredNot checked
Do I need both?
ARC doesn't favour either. Other write-ups often say support both. ARC only reports the column it can count.
How to check your store
Paste the address at /agent-checkout. That checks UCP and the catalog. It does not detect ACP.
Frequently asked questions
- UCP vs ACP: what's the difference?
- UCP and ACP are both open standards for letting AI agents buy from stores. UCP, from Google and partners, covers the wider shopping journey through a profile at /.well-known/ucp. ACP, from OpenAI and Stripe, focuses on the checkout handshake. ARC measures UCP adoption across thousands of stores; ACP is not yet measured.
- Should I support UCP or ACP?
- Many sources recommend both. ARC doesn't favour either; it reports what it measures.
- Which is more widely adopted?
- ARC measures UCP but not ACP yet, so it can't make a fair comparison.
- Are both open source?
- Yes, both are published openly.
On ARC
Cite this: ARC, arcreport.ai, accessed 2026-10-13, CC-BY-4.0. Protocol figures: ARC saved checks, accessed 2026-10-13 (13 October 2026). Index browser figures: ARC open dataset snapshot 2026-10-12. Platform figures: ARC saved checks, accessed 2026-10-13.
Every figure is labelled Measured, Inferred or Not measured. Not measured is not zero. A missing result is not a mark against a store. ARC stops before payment.