Payments

Pages

• x402 (HTTP 402 + EIP-3009) — Coinbase-led standard. Sub-cent USDC payments over Base. The first concrete adapter on the PaymentBroker SPI.

When to think about payments

You don't need a payment broker for free internal multi-agent traffic — the default is PaymentBroker.noOp() (the NoOpPaymentBroker singleton). Accountability machinery threads through untouched. Reach for a real broker when:

• Your agent calls third-party services that charge per request — premium MCP servers, paid embedding endpoints, paid weather/news feeds. With x402, the server returns HTTP 402 and your broker auto-settles the micropayment; the response comes back as if you'd called a free endpoint.
• Your agent offers a paid service to other agents outside your trust boundary. Quote the price, accept the signed authorisation, settle on-chain (or via Stripe, Lightning, etc. — once those adapters ship).
• You need an audit trail showing exactly how much each agent spent and on what. Every settlement emits an AgentLiabilityRecord for downstream compliance.

Architecture

                                Quote(payer, payee, service)
                                Settlement {Settled | Rejected | Expired | AlreadySettled}
                                          │  ▲
                                          ▼  │
┌──────────────────────────────────────────────────────────────┐
│ PaymentBroker (SPI, tnsai-core)                              │
└──────────────────────────────────────────────────────────────┘
                                          │
        ┌─────────────────────────────────┼──────────────────────────┐
        ▼                                 ▼                          ▼
  PaymentBroker.noOp()           X402PaymentBroker            (future adapters)
  - default (core)               - tnsai-payments              - Stripe
  - free internal traffic        - x402 / EIP-3009             - Lightning
  - quotes at $0.00              - Base mainnet + Sepolia
                                 - Wallet SPI for signing

The broker is the layer between your agent's chat loop and whatever rail moves the money. The rest of this section walks you through wiring it up.

Related

• Security: Accountability — AgentLiabilityRecord audit trail every broker emits to.
• Security: Cost Governance — pair CostBudget (broad LLM spend) with AuthorityScope.spendCeilingUSD (per-broker mandate) for layered controls.
• Reference: SPI — PaymentBroker contract.