x402
A payment protocol that uses the HTTP 402 status code to enable machine-to-machine payments with USDC.
HTTP 402 ("Payment Required") has existed since the early web but was never widely implemented. The x402 protocol brings it to life by enabling instant micropayments with USDC.
Here's how it works: when a client requests a paid resource, the server responds with a 402 status code and payment details. The client automatically sends USDC to the specified address, and the server grants access. This all happens programmatically without human intervention.
The use cases are exciting: AI agents paying for API calls, pay-per-article content, machine-to-machine commerce, and micropayments too small for traditional payment processors. x402 makes USDC programmable money in the truest sense.
Related Terms
Micropayment
A very small financial transaction, typically under $1, that's impractical with traditional payment processors.
USDC (USD Coin)
A regulated, fully-backed stablecoin pegged to the U.S. dollar. Each USDC is redeemable for $1.
Smart Contract
Self-executing code deployed on a blockchain that automatically enforces the terms of an agreement.
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This definition is provided for educational purposes. USDC.org is an independent resource and is not affiliated with Circle Internet Financial.