Alchemy adds x402 SIWE gateway for USDC API payments

Alchemy has launched an x402 gateway authentication option that lets agents use Sign-In With Ethereum from a local EVM wallet and USDC on Base to pay for API responses. The company announced the capability on February 26, 2026 and the documentation snapshot is current as of September 26, 2026.

Under the gateway, an agent holds an EVM private key and signs a SIWE message. The signed SIWE token is attached to API requests and serves as both identity and payment source. When a paid request needs credits, Alchemy returns an HTTP 402 payment challenge with instructions. The agent then settles the charge in USDC on Base using x402 rails. Alchemy’s documentation states the firm uses Coinbase’s CDP facilitator to verify and settle those payments and then applies the funded credit balance to subsequent API calls.

The gateway exposes the same API surface available to key-based clients. That includes Node RPC methods (standard eth_* methods and Alchemy enhancements across more than 100 chains), Token, NFT, Transfers, Prices, Portfolio and Simulation APIs. The difference is in how requests are authenticated and how payments are settled.

To use the gateway, operators need a Node.js environment with npm and the Alchemy CLI. The CLI is installed via npm and the wallet is connected in local mode or by pointing the CLI to a key file. The gateway is enabled with alchemy config set x402 true or the global –x402 flag on commands. Example CLI commands in the documentation include alchemy wallet connect –mode local, alchemy config set wallet-key-file /secure/path/evm.key, and alchemy –json –no-interactive –x402 evm data price symbol ETH,BTC,SOL.

Agents must fund the EVM address with USDC on Base to pay top-ups. The February 26 announcement notes agents can start with about $1 in compute credits on the pay-as-you-go tier. The first paid call typically triggers a 402, the agent pays the top-up, and subsequent calls draw down the credited balance. A wallet with no USDC on Base will stall on every paid call until it is funded.

The documentation advises treating the gateway key as production signing material: restrict filesystem permissions, rotate keys on a schedule, and avoid embedding private keys in skills, public repositories or chat logs. Operators should maintain a small ETH balance or a sponsored-gas option if the same key is used to sign on-chain transactions. Session limits or allowlists can limit how much an agent can spend from the wallet.

The CLI includes diagnostics such as alchemy doctor and alchemy config status to surface missing configuration before running paid calls. The CLI supports –json and –no-interactive flags to prevent prompts from blocking automated agents. Alchemy also provides optional MCP and Agent Skills tooling and documents MCP registration commands for conversational agent integration.

The documentation distinguishes two CLI surfaces. Enabling x402 with alchemy config set x402 or the –x402 flag activates the gateway that pays Alchemy. The alchemy x402 request command is a separate client for paying compatible third-party x402 v2 endpoints. Browser- or device-based alchemy auth and API keys remain the method for Admin API app management and human developer workflows. Gateway SIWE requires an EVM wallet; Solana wallets in the CLI can sign Solana transactions but are not accepted as the gateway auth identity at this time.

For teams that need to verify and settle inbound payments to their own resource servers or use other facilitators, Alchemy’s documents point to selecting an x402 facilitator rather than using the gateway. The gateway option provides a way for agents to authenticate and pay for Alchemy APIs with a wallet identity and USDC on Base without using long-lived human API keys.