x402 Protocol

The x402 protocol enables AI agents to subscribe or purchase credits on CheapestInference autonomously — no human setup required. Agents pay with USDC on Base L2 and receive an API key instantly.

How it works

1. Agent sends a request to any inference endpoint without an API key
2. The server responds with 402 Payment Required including a product catalog
3. Agent selects a product (subscription or credit package) and pays via USDC on Base
4. Agent receives an API key and uses it for all subsequent requests

402 response format

When a request arrives without an API key, the response includes available products:

{
  "error": "Payment Required",
  "x402": {
    "version": 1,
    "accepts": [
      {
        "scheme": "exact",
        "network": "base",
        "asset": "USDC",
        "payTo": "0x...",
        "maxTimeoutSeconds": 300,
        "extra": {
          "name": "CheapestInference",
          "facilitatorUrl": "https://...",
          "products": [
            { "type": "subscription", "plan": "standard", "price": "20", "duration": "30 days" },
            { "type": "subscription", "plan": "pro", "price": "60", "duration": "30 days" },
            { "type": "credits", "minAmount": "10", "description": "Pay-as-you-go credits" }
          ]
        }
      }
    ]
  }
}

Products

Product	Price	What you get
Standard subscription	$20 USDC	30-day API key, 60 RPM, 3,333 TPM
Pro subscription	$60 USDC	30-day API key, 200 RPM, 13,333 TPM
Credits	$10+ USDC	Pay-as-you-go balance, 60 RPM, never expires

Agent flow

# 1. Agent requests without key
curl /v1/chat/completions
→ 402 Payment Required
  { "products": [...], "network": "base" }

# 2. Agent subscribes with USDC
curl -X POST /api/billing/checkout
  -d '{"planSlug": "pro", "method": "usdc"}'
→ { "address": "0x...", "amount": "60" }

# 3. Agent sends USDC and verifies
curl -X POST /api/billing/verify-usdc
  -d '{"txHash": "0xabc...", "planSlug": "pro"}'
→ { "apiKey": "sk_live_..." }

# 4. Agent uses key for inference
curl /v1/chat/completions
  -H "Authorization: Bearer sk_live_..."

Agent discovery (A2A)

CheapestInference serves an agent card at:

GET /.well-known/agent.json

This follows the Google A2A protocol and advertises:

• Available skills (inference, model listing)
• Supported auth methods (bearer key, x402)
• Streaming capability
• API endpoint URL

Agents can discover CheapestInference and autonomously decide to subscribe or purchase credits.

Why not pay-per-request?

Pay-per-request doesn’t work for AI inference because request costs vary wildly depending on the model and token count. A flat $0.002 request to a model that costs $2/M tokens on a 100K prompt would lose money. Subscriptions and credits ensure sustainable pricing while giving agents full autonomy.