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Agent settlement

Agent settlement is Stable's rail for machine payments. An agent holds a USDT0 balance, pays for a resource over HTTP, and the payment settles on-chain in the same request cycle. The agent spends down from one balance for both the payment and the network fee. There is no separate gas token, no sign-up, and no API key rotation.

Why this matters for agents

Agents transact differently from humans. They run continuously, make many small payments, and cannot complete sign-up flows or rotate API keys. Settlement on Stable matches that workload:

  • USDT0 is the gas token and the payment token. An agent wallet holds a single asset and spends it down for both fees and payments.
  • Sub-cent, predictable fees. Fees are denominated in dollars, so agents can budget cost per action without converting from a volatile gas asset.
  • Sub-second finality. A paid HTTP call settles inside the request lifecycle (~700 ms block time), which makes high-frequency machine traffic viable.
  • USDT distribution. USDT is the most widely held stablecoin; Stable is the venue purpose-built for it.

How the layers fit

Two layers do different jobs and are complementary, not alternatives:

  • x402 is the payment standard. It is an HTTP-native protocol where a server responds with 402 Payment Required, a client signs an authorization, and a facilitator submits it.
  • MPP (Machine Payments Protocol) is the IETF-track standard that supersedes x402 with broader intents and multi-rail support; x402 is the backward-compatible subset Stable supports today. See MPP.
  • Stable is the settlement layer. It is where the on-chain transfer of USDT0 actually happens.

A facilitator sits between the two: it verifies the signed payment and submits the on-chain call so the developer does not run settlement infrastructure. See Facilitators for the providers that support Stable today.

agent (client)  ──HTTP──▶  resource server  ──signed payment──▶  facilitator  ──tx──▶  Stable
                          (returns 402)                          (verify + submit)     (USDT0 settles)

What you can build

  • Pay-per-call APIs priced per request in USDT0, settled via x402 or MPP.
  • Agent-to-agent commerce where one agent pays another for a service over HTTP.
  • Paid MCP tools that wrap x402 endpoints so an AI client calls and pays for them through prompts.
  • Autonomous procurement against a budgeted USDT0 balance.
  • Usage-based billing that settles per request instead of per invoice.
  • Agent wallets funded with USDT0 only, no custodial middleware.

Start here

Next recommended

  • x402 in depth — Read how the HTTP payment protocol works end to end on Stable.
  • MPP — The broader IETF-track standard that x402 belongs to.
  • Facilitators — See which facilitators already settle USDT0 payments on Stable.