> ## Documentation Index
> Fetch the complete documentation index at: https://stablelabs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Agent settlement

> How autonomous agents hold, pay, and settle in USDT on Stable, with no separate gas token and sub-second finality.

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](/en/explanation/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](/en/reference/agentic-facilitators) for the providers that support Stable today.

```text theme={"dark"}
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

<CardGroup cols={2}>
  <Card title="Build a pay-per-call API" icon="zap" href="/en/how-to/build-pay-per-call">
    Stand up an x402-gated endpoint and settle a real USDT0 payment in the request.
  </Card>

  <Card title="Build an MPP endpoint on Stable" icon="code" href="/en/how-to/build-mpp-endpoint">
    Write the three MPP custom-method hooks for USDT0 and settle on Stable.
  </Card>

  <Card title="Develop with AI" icon="sparkles" href="/en/how-to/develop-with-ai">
    Wire Docs MCP and Runtime MCP into your AI editor and paste the Stable context block.
  </Card>

  <Card title="Pay with an MCP server" icon="bot" href="/en/how-to/pay-with-mcp">
    Expose x402-paid APIs as MCP tools an agent can call through natural-language prompts.
  </Card>
</CardGroup>

## Next recommended

<CardGroup cols={3}>
  <Card title="x402 in depth" icon="globe" href="/en/explanation/x402">
    Read how the HTTP payment protocol works end to end on Stable.
  </Card>

  <Card title="MPP" icon="layers" href="/en/explanation/mpp">
    The broader IETF-track standard that x402 belongs to.
  </Card>

  <Card title="Facilitators" icon="server" href="/en/reference/agentic-facilitators">
    See which facilitators already settle USDT0 payments on Stable.
  </Card>
</CardGroup>