AI Agent payment 7-protocol layering table

Wiki route

This entry sits under AI Agent payment protocol overview · seven-protocol map. Read it against payments index for peer / contrast context and systems index for the broader system / regulatory boundary.

Key facts

• 7 protocols = intent 3 + transport 2 + context 2 ^•
• AP2(Google-led) + x402(Coinbase-led) + MCP (Anthropic-led) + A2A (Google-led) = the industry shorthand “4 protocols” ^•
• SPT (Skyfire) / ACK (Catena Labs · a16z) / TAP (xpay) are secondary competitors ^•
• AP2 signs mandates with VC (Verifiable Credentials) + DPK (Decentralized Public Key) ^•
• x402 is an HTTP standard, non-chain-specific ^•

Mechanism / How it works

The intent layer answers “what does the user want to do.” AP2 defines a 3-layer trust-chain mandate: Intent (user ↦ agent · authorize purchase of X) → Cart (agent ↦ merchant · place the order on the user’s behalf) → Payment (merchant ↦ payment network · collection instruction). Each layer is signed with VC + DPK, forming a chain that is tamper-proof. SPT / ACP are early competitors of similar design.

The transport layer answers “how to move money from A to B.” x402 revives the HTTP 402 Payment Required status code. The server embeds “pay X USDC to address Y” in the response · the agent wallet automatically signs · transfers. Per-call micropayment is established. The underlying wallet is usually based on ERC-4337 smart accounts or ERC-7702 temporary upgrades, and when going cross-chain, chain abstraction patterns hide the differences of the underlying chains. TAP is a similar token-based auth path but with a thinner ecosystem.

The context layer answers “how does the LLM know the available tools / data.” MCP standardizes server-side tool definitions + resources · the LLM client automatically discovers and invokes them. A2A takes on agent-to-agent communication (one agent delegating to another) · forming a complementary relationship with MCP’s server-tool in the 2 direction of agent-agent.

Origin & evolution

2024.11 Anthropic released MCP · within 6 months OpenAI / Google followed · it became the de facto standard. 2025.04 Google released A2A to complement agent-to-agent communication. 2025.05 Coinbase released x402 , igniting the “HTTP-native payment” narrative (for detail on USDC as the default settlement currency see USD stablecoin interchange layer). 2025.09 Google, with 60+ partners, released AP2 · setting the tone of the intent layer. In mid-2026 FIDO took over AP2 → pivoted to AAIF · the intent layer heads toward a neutral standard. Secondary protocols (SPT/ACP/TAP) appeared within 2025, but under the dual commoditization pressure of AP2 + FIDO they find it hard to build an independent moat — forming a structural contrast with Stripe protocol-hedging strategy.

Related

• Wiki Index
• seven-protocol overview
• protocol commoditization and upward migration of value

Sources

• Google AP2(intent layer · Intent / Cart / Payment mandate · VC + DPK signature) — https://github.com/google-agentic-commerce/AP2
• Coinbase x402(transport layer · HTTP 402 per-call micropayment) — https://github.com/coinbase/x402
• Model Context Protocol (context layer · server-tool interface) — https://github.com/modelcontextprotocol/modelcontextprotocol
• Agent2Agent (A2A) Protocol (context layer · agent-agent communication) — https://github.com/a2aproject/A2A
• Agent Commerce Kit (Catena Labs · ACP-family intent / payment design) — https://www.agentcommercekit.com/overview/concepts
• Skyfire Developer Docs (SPT-family · Identity and Payments for AI) — https://docs.skyfire.xyz/