x402 Payments

Compose.Market uses the x402 protocol (v2) for machine-to-machine payments. Every paid request follows the same pattern: the API asks for payment, the client pays, the API returns the result.

The 402 flow

Payment methods

Method	Header	Use case
Compose Key	`Authorization: Bearer compose-<jwt>`	External tools (OpenCode, Cursor, Cline), first-party app sessions, SDK calls
Raw x402	`PAYMENT-SIGNATURE`	Wallet-native clients that sign EIP-712 payloads and retry

Compose Key

A bearer token that handles payment server-side. The SDK creates and stores it automatically.

curl https://api.compose.market/external/v1/chat/completions \
  -H "Authorization: Bearer compose-abc123..." \
  -H "Content-Type: application/json" \
  -d '{"model": "gpt-5.5", "messages": [{"role": "user", "content": "Hello"}]}'

Raw x402

For wallet-native clients, the server returns 402 with a PAYMENT-REQUIRED header. The client signs and retries with PAYMENT-SIGNATURE:

curl -X POST https://api.compose.market/v1/chat/completions \
  -H "PAYMENT-SIGNATURE: <base64-eip712-signature>" \
  -H "Content-Type: application/json" \
  -d '{"model": "gpt-5.5", "messages": [{"role": "user", "content": "Hello"}]}'

The x402 payload uses x402Version: 2 and an amount field.

x402 schemes

Scheme	How it works	When to use
batch-settlement	Deposit USDC into an on-chain escrow channel once. Each request signs an off-chain voucher. The server claims vouchers in batches.	High-volume repeated calls (agent endpoints). Lowest per-request cost.
exact	Sign an EIP-3009 transfer for the exact advertised amount.	One-shot calls, no pre-funding.
upto	Sign a Permit2 authorization for a maximum. The server charges the measured usage after processing.	Usage-metered calls (LLM token billing).

Pricing

The API applies a 1% platform fee on top of the raw provider amount. Pricing is dynamic — each model’s price comes from the generated catalog, not a fixed table.

OpenRouter charges 5.5%. Compose charges 1%. That is a 5.5x difference, and it is factual.

Multi-chain support

Payments settle in USDC on 6 chains:

Chain	Chain ID	Type
Avalanche Fuji	43113	Testnet
Avalanche C-Chain	43114	Mainnet
Arbitrum Sepolia	421614	Testnet
Arbitrum One	42161	Mainnet
Base Sepolia	84532	Testnet
Base	8453	Mainnet

The X-CHAIN-ID header selects the settlement chain. Examples in these docs use 43113 (Fuji).

x402 Facilitator — protocol reference, verify/settle endpoints
SDK Payments — TypeScript API for Compose Keys and raw x402
Sessions & Keys — pre-approved spending limits
Metering — how provider output becomes a bill

Getting Started

Concepts

The 402 flow

Payment methods

Compose Key

Raw x402

x402 schemes

Pricing

Multi-chain support

​The 402 flow

​Payment methods

​Compose Key

​Raw x402

​x402 schemes

​Pricing

​Multi-chain support

​Related

The 402 flow

Payment methods

Compose Key

Raw x402

x402 schemes

Pricing

Multi-chain support

Related