Protocol x402: How AI Agents Will Pay for Services Online

Everyone is familiar with the 404 error code, but few have heard of the 402 status “Payment Required.” Developed decades ago, it never saw widespread adoption. However, with the dawn of the artificial intelligence era, this could change dramatically.

What the x402 Standard Represents

x402 is an open protocol designed to simplify online payments, making them as effortless as loading a web page. Announced by Coinbase in May 2025, the initiative focuses on AI agents that can autonomously conduct transactions using stablecoins.

The foundation of the modern internet is the HTTP protocol, which uses various status codes:

• HTTP 200 — Successful request;
• HTTP 404 — Resource not found;
• HTTP 500 — Internal server error.

Among them is the rarely used HTTP 402, meaning “Payment Required.” It was originally conceived for premium content payment but wasn’t implemented due to the lack of a convenient infrastructure.

x402 aims to fix this. When a service requires payment, it sends the agent not just a notification, but a detailed request specifying the amount, wallet address, and currency. The agent, in turn, can automatically confirm and execute the transaction on the blockchain. Essentially, x402 becomes a mechanism allowing machines to pay for each other’s services, turning stablecoins into “fuel” for the digital economy.

Why HTTP 402 Wasn’t Used Before

The widespread adoption of the 402 code was hindered by economic reasons. Since micropayments through traditional systems (Visa, Mastercard) were unprofitable due to high transaction fees, advertising became the internet’s primary business model. Paying a dollar in fees to access content costing five cents is economically unviable.

Blockchain technology solves this problem by offering minimal fees, making micropayments financially feasible.

Who is Already Adopting x402

The x402 ecosystem is still in its early stages but is attracting attention from projects related to AI and decentralized services. A key development was the endorsement from Google, which, together with over 60 companies (including Coinbase, PayPal, Mastercard, and Salesforce), is working on integrating this standard for future agent-to-agent payments.

Analytical platforms have already begun listing crypto assets in the x402 category. This list includes 41 projects with a total market capitalization of approximately $800 million. Volume leaders include:

• EigenCloud (EIGEN) — $440 million;
• FLock (FLOCK) — $60 million;
• Bankr (BNKR) — $50 million.

Network activity is also growing: in the last week of October, over 550,000 transactions were recorded from 40,000 unique users, totaling around $600,000 in USDC stablecoins.