ACP or UCP? The question assumes you have to pick one. You don't — and by mid-2026 they aren't even doing the same job.
ACP and UCP are not two competing implementations of the same standard. They sit at different layers, and most of the work required for one is the same work required for the other.
Protocol status as of June 2026. Both specs are moving. Verify current spec versions before you implement — I've dated every claim below for that reason.
What changed in March 2026
ACP — the Agentic Commerce Protocol, backed by OpenAI and Stripe — launched as the standard behind ChatGPT Instant Checkout. Agent finds product, agent buys product, merchant stays merchant of record.
