Protocol Comparison
Four protocols. Eight stages. One map.
Every agentic payment protocol covers a different slice of the lifecycle. This matrix shows where each operates and where they converge.
x402
HTTP-native payment protocol.
Built by Coinbase. x402 turns any HTTP endpoint into a paid resource using the 402 status code. Strongest at Transport (Stage 5) and Facilitation (Stage 7) — the actual payment header exchange and on-chain settlement via CDP. Operates on Base L2.
Coverage: 6 of 8 stages. Chain: Base (Ethereum L2). Facilitator: Coinbase CDP. Settlement: USDC on-chain.
ACP
Agent Commerce Protocol.
Built by Stripe. ACP uses Shared Payment Tokens and Stripe Link for identity. Strongest at Identity (Stage 2) with KYC-backed credentials and Authorization (Stage 6) via Stripe's payment infrastructure. Bridges fiat and crypto rails.
Coverage: 6 of 8 stages. Chain: Fiat + crypto. Facilitator: Stripe. Settlement: Stripe payment methods + USDC.
AP2
Agent Payments Protocol.
Built by Google. AP2 starts from signed user mandates at Intent (Stage 1) — cryptographic delegation of payment authority. Uses A2A (Agent-to-Agent) protocol for discovery and can extend with x402 for crypto settlement at Stages 4–5.
Coverage: 6 of 8 stages. Chain: Multi-rail. Facilitator: 60+ payment partners. Settlement: Fiat + x402 crypto extension.
ACK
Agentic Commerce Kit.
Built by Coinbase. ACK focuses on the agent identity problem — verifying autonomous agents before they can transact. Concentrated at Identity (Stage 2) with ACK-ID credentials and Facilitation (Stage 7) via AgentKit.
Coverage: 3 of 8 stages. Chain: Base. Facilitator: Coinbase AgentKit. Settlement: USDC via AgentKit.
Convergence
Where protocols converge.
x402 and AP2 share Stages 3–5 through the A2A x402 extension. AP2 handles intent and discovery, then hands off to x402's HTTP header exchange for the payment transport. This is the convergence zone — two protocols operating in tandem.