HTTP 402 + USDC: Pay-per-use AI APIs for Autonomous Agents

ntriq-gh — Tue, 07 Apr 2026 23:02:13 +0000

The Problem with API Keys for AI Agents

AI agents need to call external APIs autonomously. But traditional API key auth has a fundamental mismatch:

Who manages the keys? The agent can't sign up for accounts
How does billing work? Subscription tiers don't fit pay-per-task usage
What about multi-agent systems? Keys get shared, leaked, revoked

There's a better way: let agents pay directly, per request, with crypto.

x402: HTTP 402 as a Payment Protocol

The HTTP 402 status code has been "reserved for future use" since 1991. x402 finally uses it.

The flow:

Agent → POST /document-intel
Server → 402 Payment Required
        { amount: "0.05", currency: "USDC", network: "eip155:8453" }
Agent → EIP-3009 signature (gasless transfer authorization)
Server → Facilitator validates → 200 OK + result

No API keys. No subscriptions. No gas fees. The payment IS the authentication.

ntriq AgentShop: 6 Endpoints, $0.01–$0.05

We built a document intelligence server on this protocol, running 100% local inference on a Mac Mini.

Endpoint	Price	Model
`/document-intel`	$0.05	qwen2.5vl:7b
`/invoice-extract`	$0.03	qwen2.5vl:7b
`/screenshot-data`	$0.02	qwen2.5vl:7b
`/alt-text`	$0.01	qwen2.5vl:7b
`/pii-detect`	$0.02	qwen2.5:7b
`/sentiment`	$0.01	qwen2.5:7b

Cost to run: $0 (local inference). Margin: ~100%.

Try It

# Step 1: Hit the endpoint — you'll get a 402 back
curl -X POST https://x402.ntriq.co.kr/sentiment \
  -H 'Content-Type: application/json' \
  -d '{"text": "This product is amazing"}'

# Response:
# { "x402Version": 1, "accepts": [{ "amount": "10000", "currency": "USDC" }] }

# Step 2: Sign with EIP-3009 and retry
# The x402 client library handles this automatically

Why Local Inference?

Zero marginal cost: Every request is pure profit
No rate limits: Mac Mini handles concurrent requests
Privacy: Documents never leave our infrastructure
Speed: No network hop to OpenAI

qwen2.5vl:7b handles documents, invoices, and screenshots with accuracy comparable to GPT-4V for structured extraction tasks.

MCP Integration

ntriq-agentshop is available as a ClawHub skill. Any agent using OpenClaw or Claude can discover and use these endpoints automatically.

# Install via ClawHub
clawhub install ntriq-document-intelligence-mcp

Forem: ntriq-gh