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7/21/2026
ACP vs AP2: the two AI-checkout protocols, and what your store actually has to build

ACP vs AP2: the two AI-checkout protocols, and what your store actually has to build

Short summary

OpenAI's ACP and Google's AP2 are two competing protocols for AI-agent checkout, solving the same problem in opposite ways. ACP gives agents a server-side checkout session with shared payment tokens; AP2 uses signed JWTs with canonical JSON cart hashes for price guarantees. The author implemented both and shares field notes, including a subtle canonical-JSON gotcha that cost a day of debugging.

  • •ACP (OpenAI): server-side checkout sessions with integer minor units and shared payment tokens via Stripe
  • •AP2 (Google): signed JWT cart guarantees with decimal major units and canonical JSON (RFC 8785) for hash consistency
  • •Key gotcha: AP2 cart_hash requires byte-identical canonical JSON across all SDKs or verification fails

Generated with AI, which can make mistakes.

#ai-tools#ai-agents#product-launch#industry-adoption
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