Protocol Ecosystem

The building blocks
of agentic commerce

Seven protocols from four organizations are defining how AI agents, merchants, and wallets transact with stablecoins. Each protocol maps to a specific STP stage and compliance domain — together they cover the full payment lifecycle.

ACK-ID
Agent Commerce Kit — Identity
Production

W3C DID + Verifiable Credential framework for autonomous agent identity. Establishes principal→agent delegation chains with cryptographic proof.

Skills Pairingcoinbase/agentkit Authenticate→ S2 Identity, T6 blue, code-enforced Gate
Catena Labs \u00b7 MIT \u00b7 S2 Identity
ACK-Pay
Agent Commerce Kit — Payment
Production

Transport-agnostic payment negotiation protocol with cryptographic receipts as Verifiable Credentials.

Catena Labs \u00b7 MIT \u00b7 S4 Negotiation
x402
HTTP 402 Payment Required Protocol
Production

HTTP-native micropayment protocol using the 402 status code. Server declares price, client pays in stablecoin, server delivers content.

Skills Pairingcirclefin/skills + coinbase/agentkit use-usdc + Send→ S5 Transport + S6 Authorization, Transfer + Execution domains
Coinbase / x402 Foundation \u00b7 MIT \u00b7 S5 Transport
ACP
Agent Commerce Protocol
Production

Coinbase protocol for agent-to-agent commerce. Builds on CDP AgentKit for wallet-native authorization and multi-step transaction flows.

Skills Pairingcoinbase/agentkit Send + Trade→ S6 Authorization, T3 orange, code-enforced Gate
Coinbase \u00b7 Apache-2.0 \u00b7 S6 Authorization
AP2
Agent-to-Agent Payment Protocol
Spec

Circle protocol for agent payment negotiation. Uses USDC-native flows with compliance metadata embedded in transaction payloads.

Skills Pairingcirclefin/skills use-usdc + use-gateway→ S5 Transport, T5 teal, policy-enforced Monitor
Circle \u00b7 Apache-2.0 \u00b7 S5 Transport
UCP
Universal Checkout Protocol
Announced

Stripe protocol for stablecoin payment discovery and method negotiation at the merchant checkout layer.

Stripe \u00b7 Proprietary \u00b7 S3 Discovery
MPP
Machine Payments Protocol
Testnet

Tempo network protocol for machine-to-machine payments. Dedicated payment lanes with TIP-403 Policy Registry for compliance routing.

Skills Pairing(no published skill yet) —→ S5 Transport, T5 teal, Tempo TIP-403 Policy Registry
Tempo (Stripe/Paradigm) \u00b7 Apache-2.0 \u00b7 S5 Transport

STP Mapping

How protocols map to the 8 STP stages

The Stablecoin Transfer Protocol defines 8 stages that every stablecoin payment passes through. Each protocol above maps to one or more stages — its domain color and stage number tell you where in the lifecycle it operates.

Full STP specification on StableSTP.com →