Coinbase's x402 payment protocol — built on HTTP's long-dormant 402 Payment Required status code — shipped three major upgrades on March 17, expanding what AI agents can pay with and how developers can monetize AI tooling.

Any ERC-20 Token

Previously, x402 transactions were primarily limited to USDC. The v2 update adds support for any ERC-20 token using the EIP-3009 and Permit2 standards. Developers can now accept USDC, EURC, meme coins, or any other Ethereum-compatible token as payment — with no extra bridging or wrapping required.

Sign-In With X (SIWX)

A new Sign-in-with-X feature solves a friction point for paid content: customers who have already paid can now authenticate via their wallet to regain access without re-paying. The system supports both EVM and Solana wallets, making it portable across chains.

MCP Tool Monetization

The most developer-facing addition is the x402 MCP package, which lets any MCP tool be monetized directly. Developers can attach a payment gate to any tool in an AI workflow — an agent that calls a weather API, a code executor, or a search index can now pay per-use in a single transaction without any custom payment integration.

Why It Matters

x402 sits at the intersection of two fast-moving trends: autonomous AI agents and on-chain payments. With Base as its native home and Coinbase providing the infrastructure, x402 is positioning itself as the default payment rail for agentic systems — the layer where AI agents settle transactions without needing a human to authorize each one. The MCP integration in particular signals a clear bet that AI agent tooling will become a paid marketplace.