[DigitalToday reporter Yoonseo Lee] Circle has released an official USDC payment specification for the Machine Payments Protocol (MPP).

On June 23 local time, blockchain outlet The Defiant reported that the specification standardised how artificial intelligence (AI) agents and automated services pay in USDC on EVM-compatible blockchains and Solana.

There are three main points. It set out a standard payment interface for agents to transact in USDC across supported EVM-based chains and Solana. It also added MPP’s first crosschain payment profile via Circle Gateway. It further included support for USDCx, a Stacks-based USDC-linked stablecoin.

MPP is a payment standard designed around the existing web standard HTTP 402 “Payment Required” status code. When an agent sends a request to an endpoint that supports MPP, the server returns a 402-style response. The agent then signs an off-chain USDC payment authorisation using the Ethereum standard EIP-3009 and sends the request again. Circle Gateway verifies the authorisation and places it in an on-chain batch settlement queue.

This structure does not require a separate API key. Each request is identified by a wallet address and transaction hash. Automated services or AI agents make payments without human involvement, while settlement tracking is recorded on the blockchain basis.

A key point of the specification Circle released is that it elevated USDC to an official payment method within MPP. MPP already included payment specifications related to cards, EVM, Lightning, Solana, Stellar and Stripe, and USDC has now been added as a named payment method. The protocol was developed by Tempo Labs and Stripe engineers, and has been formally proposed to the Internet Engineering Task Force (IETF).

The expansion of supported assets also stood out. USDCx is a USDC-based stablecoin issued on Stacks, a leading Bitcoin layer-2 network. Stacks said USDCx is fully collateralised by USDC held in Circle xReserve and provides cryptographic proof in the deposit and issuance process. This extends MPP’s payment scope to Bitcoin-layer settlement.

The announcement did not include figures for actual users, transaction volumes or adoption indicators. It shows the release of the standard itself is the priority stage.

The market is also seeing faster competition over machine-to-machine commerce infrastructure. On the same day, 0x Protocol began supporting autonomous agent payments in its swap API. AI agents can use swap functions by paying $0.01 in USDC per request through x402 or MPP, without API credentials.

Earlier in June, Amazon Web Services (AWS) connected Coinbase’s x402 protocol to CloudFront to enable AI agents to pay content usage fees in USDC. Coinbase also released standalone agent accounts that same week. Mastercard opened its card payment network to AI agents through the AP4M network with more than 30 cryptocurrency partners. Circle also began gas-free micro-payments in April across 11 EVM chains.

Ultimately, the release of the specification is a move to incorporate USDC as an official payment method within MPP’s open standard. As machine-to-machine transactions are broken down into unit payments such as API calls, content access and swap requests, Circle has laid out a framework to secure both crosschain settlement and stablecoin-based payment standards at the same time.

We've published an official @USDC method spec for @mpp (Machine Payments Protocol) The spec gives developers: → A standardized way for agents to transact in USDC across supported EVM chains and Solana → The first crosschain payment profile in MPP via Circle Gateway → Support… pic.twitter.com/yMuCqWTNRB