BlockRun glossary

HTTP-native payment standard. Server returns 402; client signs USDC payment; retries with payment header.

x402 is an HTTP payment protocol that pairs the standard 402 Payment Required status code with stablecoin settlement. A resource server returns 402 with structured payment requirements; the caller signs an EIP-3009 TransferWithAuthorization locally and retries with a payment header. Non-custodial, instant settlement.

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Billing model where each API call is priced and settled individually — no subscription, no minimum.

Pay-per-call AI charges per individual API call, typically per-token for LLMs and per-asset for media generation. No monthly fee, no prepaid balance. Designed for autonomous AI agents that can't hold credit cards.

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Stablecoin issued by Circle, pegged 1:1 to the US dollar. The settlement asset for x402 on BlockRun.

USDC is a fully-reserved stablecoin issued by Circle. BlockRun settles every API call in USDC on Base, Solana, or XRPL. The contract on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913.

Ethereum standard that lets a caller authorize a USDC transfer with an off-chain signature.

EIP-3009 defines a TransferWithAuthorization function on ERC-20 tokens (including USDC) that lets a holder sign an off-chain message authorizing a future transfer. The signature is what the x402 client sends in its payment header. The server submits it on-chain when fulfilling the request.

The on-chain settlement service that verifies x402 payment authorizations and submits them to the chain.

A facilitator is the bridge between an x402 server and the blockchain. It verifies the signed payment authorization and submits the settlement transaction. BlockRun uses Coinbase CDP as the primary facilitator with PayAI as fallback.

A single API endpoint that routes requests to multiple AI providers (OpenAI, Anthropic, Google, etc.).

An AI gateway is a unified API in front of many model providers. It normalizes the request/response shape (typically OpenAI-compatible), handles auth and billing, and often adds capabilities like fallback, caching, and observability. BlockRun is a pay-per-call AI gateway.

Open protocol from Anthropic for connecting LLMs to tools and data sources.

MCP (Model Context Protocol) is an open standard for exposing tools, prompts, and resources to LLM clients like Claude Code, Cursor, and ChatGPT. BlockRun ships an MCP server with 10 tools (chat, search, exa, markets, surf, price, dex, phone, models, wallet) installable via 'claude mcp add blockrun'.

A very small payment, typically under one cent, that's only economical with very low-fee settlement rails.

Micropayments are sub-cent payments. Traditional payment rails (credit cards, ACH) have fixed fees that make these uneconomical. Stablecoin rails on L2s (Base, Solana) make micropayments viable — BlockRun has API calls priced as low as $0.001.

The on-chain confirmation that a payment has moved value from the payer to the recipient.

Settlement is the moment a payment becomes final on-chain. In x402, settlement happens after the resource server fulfills the request — if the request fails, no payment is taken. BlockRun returns a settlement transaction hash in the X-Payment-Receipt response header.

A backup model that handles a request when the primary model fails (timeout, rate limit, error).

BlockRun automatically falls back to a comparable model when the requested one fails — including the cross-provider chain qwen3-next-80b → gpt-oss-120b → glm-5.1 for free-tier traffic. The actual served model is surfaced via the X-Fallback-Model response header.