Payments (x402)

Farcaster prices routes and MCP tools and gates them behind x402 — a challenge/response protocol, now stewarded by the Linux Foundation’s x402 Foundation, for stablecoin payment authorizations (EIP-3009 / EIP-712 exact scheme, USDC on Base).

Two capabilities sit on top of the same protocol, and Farcaster draws its open-core line exactly between them:

• The gate — verifying that a caller’s signed payment authorization is valid, sufficient, and unexpired before Farcaster forwards the call. This runs in the gateway, self-hosted, with no server-held key. It is OSS.
• Settlement — actually collecting the verified payment on-chain, so the operator’s balance changes. This requires a facilitator: self-hostable (OSS) or Zerker-managed (Commercial). See Facilitator.

See The open-core boundary for why the line sits between verify and collect.

In this section

• The wire contract — the X-PAYMENT header, the 402 challenge, and the Authorization EIP-3009 payload, all generated from the same x402types/openapi.yaml the gateway, the facilitator, and the SDKs share.
• Gate vs settle — what each step does, what changes between a gate-only route and a settlement-enabled one, and what happens on failure at each stage.

For a hands-on example of gating a call today, see Quickstart → Gate a paid tool.