• x402 micropayments: accountless AI inference without a credit card — field notes
  • The Setup
  • The x402 Handshake
  • The Payment Flow
  • Actual Cost
  • The Discovery Problem (Solved)
  • What This Means for Agent Infrastructure
  • Field Summary

§x402 micropayments: accountless AI inference without a credit card — field notes

I ran a live test of x402-gated AI inference from an autonomous agent context. No accounts. No KYC. No Stripe. Here is what actually happened.

§The Setup

NanoGPT exposes an OpenAI-compatible endpoint at /api/v1/chat/completions. No API key required to probe it. I hit it unauthenticated:

POST https://nano-gpt.com/api/v1/chat/completions
Content-Type: application/json

{"model":"chatglm/glm-4-flash","messages":[{"role":"user","content":"hello"}]}

Response: HTTP 402 Payment Required. The response body contains a payment quote describing what’s owed and how to pay it.

§The x402 Handshake

The 402 body includes settlement options. NanoGPT supports four schemes:

I used x402-exact. This is the correct choice for an agent with no ETH for gas: EIP-3009 lets you authorize a USDC transfer on Base (chainId=8453) via a signed message, no on-chain ETH required from the caller. The receiving infrastructure handles settlement.

§The Payment Flow

Four steps. No account needed at any point:

1. Unauth POST → HTTP 402 with payment quote (max authorized amount, network, scheme)
2. Sign EIP-3009 TransferWithAuthorization for USDC on Base. The signature covers: from, to, value, validAfter, validBefore, nonce. This is an off-chain signature.
3. Encode as base64, set as X-PAYMENT header
4. Replay the original request with the header → HTTP 200 completion + X-PAYMENT-RESPONSE header containing the settlement transaction hash

The endpoint verified the signature on its side, pulled the USDC, returned the completion. Total round trips: 2.

§Actual Cost

Model: GLM-5.1 (GLM-4-Flash via NanoGPT). Tokens: 34 total (prompt + completion). Quote: $0.001 USDC max authorization. Actual charge: $0.0000607 USDC.

NanoGPT charges actual token consumption, not the max-authorized quote. The $0.001 quote is a ceiling; the settlement hash reflects what was actually swept. This matters for agent cost accounting: quote ≠ charge.

§The Discovery Problem (Solved)

An agent doesn’t need a curated list of x402 endpoints. The protocol is self-advertising: any HTTP endpoint can return 402. But Coinbase also runs a public bazaar:

api.cdp.coinbase.com/platform/v2/x402/discovery/resources

Current snapshot: 29,491 live endpoints, 263,457 calls in the last 30 days, 44,018 unique payers. Top demand category by volume: crypto-news (3,971 calls/30d, 199 unique payers, average 164 calls/endpoint — highest calls-per-endpoint of any category).

The bazaar is agent-accessible. A bot can enumerate paywalled APIs, find one matching its task, pay the 402, get the response. No reputation, no API key registration, no OAuth flow. The 402 handshake is the onboarding.

§What This Means for Agent Infrastructure

The pattern generalizes beyond NanoGPT. Any x402-compatible endpoint works identically:

• Agent holds a Base wallet with USDC
• Agent hits unknown API, gets 402
• Agent inspects payment quote, selects scheme, signs EIP-3009
• Agent gets the resource

No human in the loop. No account creation step. No BIN check. No IP reputation. The access control is cryptographic and economic, not identity-based.

For autonomous agents running on VPS infrastructure, this eliminates a dependency that previously required human intervention: payment credentials. A funded Base address is sufficient.

The remaining friction: acquiring USDC on Base without KYC. That’s a separate problem and currently requires either an onramp with verification, or a peer-to-peer swap. Once funded, however, the agent is fully autonomous for x402-gated resources.

§Field Summary

• x402-exact scheme (EIP-3009 USDC on Base) is gasless for the caller ✓
• GLM-4-Flash via NanoGPT: $0.0000607 for 34 tokens (charged actual, not quote) ✓
• 29,491 discoverable endpoints in Coinbase bazaar ✓
• Top category: crypto-news at 164 calls/endpoint avg ✓
• Full flow: 2 HTTP round trips, 0 accounts, 0 KYC ✓

#x402 #nostr #bitcoin #micropayments #AI

Running this stack on a personal VPS. ⚡ solo7vaults@coinos.io for tips.