x402 is an open payment protocol developed by Coinbase that enables instant, automatic stablecoin payments directly over HTTP. It works by reviving the HTTP 402 "Payment Required" status code, a slot that has sat in the web's specification since the 1990s but was reserved for future use. With x402, a service can charge for an API call or a piece of content, and the client, whether a human's app or an autonomous AI agent, can pay programmatically in seconds. Coinbase, which introduced x402 in 2025, framed it as a potential "WhatsApp moment" for stablecoins.
Explainer
x402: Stablecoin Payments for the Web and AI Agents
Coinbase revived a dormant web status code, HTTP 402 "Payment Required," to let apps and AI agents pay in stablecoins directly over HTTP. Here is how it works and why it matters.
How it works
The x402 payment handshake
01
Request
A client (a human app or an AI agent) requests a paid resource, such as an API call or a piece of content.
02
402 Payment Required
Instead of serving the resource, the server responds with HTTP 402 and the payment details: amount, asset, network, and where to pay.
03
Pay in stablecoins
The client signs a stablecoin payment, typically USDC on Base, and resends the request with the payment attached.
04
Verify & settle
A facilitator verifies the payment and settles it onchain. The server then returns the resource. The whole handshake takes seconds.
The protocol standardizes the payment handshake, not the entire commerce stack. A facilitator (Coinbase runs one) verifies and settles payments onchain so neither side has to manage the blockchain mechanics directly. Most activity today settles in USDC on Base, though x402 is designed to be flexible across chains and tokens.
Use cases
What x402 unlocks
Pay-per-call APIs
Monetize an API by the request, with no keys, accounts, or subscriptions. The caller pays a few cents per call.
Agent commerce
AI agents pay for data, tools, and compute autonomously, using a wallet as their native way to transact.
Metered content
Charge per article, query, or download instead of forcing a full subscription for one-off access.
Machine-to-machine
Services pay each other programmatically for resources, settling instantly in stablecoins around the clock.
The x402 ecosystem
Since launch, a growing ecosystem of services has adopted x402 to charge for APIs, data, and AI tools per request, most of them settling micro-payments in USDC on Base. Independent explorers such as x402scan track live sellers, transactions, and facilitators across the network, a useful window into how fast agent-driven, pay-per-use commerce is forming.
For the underlying money, see how stablecoin payments work and why stablecoins like USDC are suited to instant, programmatic settlement. Businesses accepting payments at scale can compare payment gateways and platforms.
The bigger shift x402 points to: money that moves at the speed of an HTTP request, payable by software as easily as by people.
FAQ
x402, answered
What is x402?
x402 is an open payment protocol developed by Coinbase that enables instant, automatic stablecoin payments directly over HTTP. It revives the long-dormant HTTP 402 'Payment Required' status code so that services can charge for APIs and content, and both humans and machines can pay programmatically. Coinbase introduced it in 2025.
How does the x402 protocol work?
When a client requests a paid resource, the server responds with HTTP 402 and the payment requirements. The client pays in a stablecoin, typically USDC on the Base network, and resends the request with proof of payment. A facilitator verifies and settles the payment onchain, and the server returns the resource. The exchange completes in seconds, with no accounts or manual checkout.
Why is x402 important for stablecoins?
x402 turns stablecoins into a native payment method for the web and for AI agents. Because a stablecoin like USDC holds a steady dollar value and settles onchain in seconds, it fits micro-payments and machine-to-machine commerce that card rails handle poorly. Coinbase described the launch as a potential 'WhatsApp moment' for stablecoins.
What is HTTP 402 Payment Required?
HTTP 402 is a status code that has existed in the web's specification since the 1990s but was reserved for future use and left largely unused. x402 puts it to work: a server returns 402 to signal that payment is required before a resource is served, along with the details needed to pay.
What stablecoins and networks does x402 use?
In practice most x402 activity settles in USDC on Base, though the protocol is designed to be chain and token flexible. Facilitators, including Coinbase, handle verification and settlement so servers and clients do not manage the onchain mechanics themselves.
Who can use x402?
Any service that wants to charge for a resource can implement x402, and any client, a person's app or an autonomous AI agent, can pay through it. It is an open standard, so it is not limited to a single company or wallet.
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