Payment Protocol Adapters

Standardized protocols for entity-to-entity payment flows.

Payment Protocol Adapters define how payments are requested and executed between entities — whether that's an agent paying for an API call, a service charging for compute, or two agents transacting with each other. These adapters sit above the core SDKs and handle the negotiation layer: "I want this resource, here's my payment, verify and deliver."

x402-sdk

Packages: • @fastxyz/x402-client — For buyers/agents making payments • @fastxyz/x402-server — For merchants/services receiving payments • @fastxyz/x402-facilitator — For verifying and settling payments

HTTP-native payment protocol based on the 402 Payment Required status code. Your agent requests a resource, the server responds with payment requirements, the agent pays, and gets access — all in a single HTTP flow.

Use cases: • Pay-per-API-call (micropayments for AI services) • Gated content or compute access • Agent-to-agent commerce

More protocol adapters coming soon: ACP (Agent Communication Protocol), Stripe integration, and others.