Stablecoins are increasingly being used as the settlement asset for a new class of machine payments, as AI agents and other software systems gain the ability to pay for digital services without a human completing each transaction.
The development is being driven by payment protocols such as x402 and Stripe’s Machine Payments Protocol, alongside infrastructure being developed by Coinbase, Circle, AWS, Cloudflare, Visa, Mastercard and Google.
The emerging model is aimed particularly at small, frequent transactions between software, including payments for application programming interfaces, data, computing resources, inference services, verification and other digital tools.
Coinbase’s x402 protocol uses the HTTP 402 Payment Required status to allow a service to request payment as part of an ordinary web request. An agent can receive the payment requirements, authorise the transaction, have it settled on-chain and retry the request with proof of payment.
That approach removes several steps associated with conventional online payments, such as creating an account, obtaining an API key, adding a payment card and purchasing credits or a subscription before using a service.
The x402 Foundation describes the protocol as an open standard for internet-native payments. Coinbase also introduced Agentic Wallets, designed to give software agents the ability to hold, send and receive funds under defined controls.
Stablecoins have emerged as the dominant settlement asset within the x402 ecosystem, with USDC accounting for almost all of the transactions analysed in recent research.
TRM Labs analysed about 198.9 million x402 settlement transactions across Base, Solana and Polygon, representing approximately $52.7 million in volume. Its analysis found that about $52.47 million of the $52.68 million examined settled in USDC, equal to roughly 99.6 per cent.
Keyrock, using research conducted with Coinbase, Tempo and Virtuals, reported a similar concentration. Its analysis of 176 million x402 payments found that 98.6 per cent of settlement volume used USDC.
However, the transaction figures do not establish that all, or even most, of the payments were made by AI agents.
TRM Labs found that x402 does not require a transaction to originate from an AI agent. Ordinary scripts, scheduled jobs and other automated processes can produce the same on-chain payment records.
After filtering out self-payments, bulk flows and other activity, TRM Labs reduced the analysed volume to about $25.62 million. It estimated that between 0.6 per cent and 7.5 per cent of that screened activity appeared to be genuinely agentic, depending on the definition used.
That estimate corresponds to approximately $154,000 to $1.92 million of the screened amount. TRM Labs also noted that its methodology could classify some single-purpose agents that repeatedly pay a single service as ordinary automated processes.
A separate July 2026 academic study reached a similar caution about raw x402 transaction counts. The researchers analysed 136.7 million settlements worth $44.1 million on Base over 280 days.
The study classified 21.2 per cent of settlements as fictitious and found that 63.78 per cent represented internal settlement within linked clusters. It identified only $187,861.35 as demonstrably reaching a nameable service.
The academic study of x402 settlement activity concluded that settlement counts can measure how easily transactions can be generated, rather than proving genuine economic adoption.
Despite those limitations, major companies are continuing to build infrastructure around machine payments.
Circle launched Circle Agent Stack in May 2026. The platform includes agent wallets, an agent marketplace, developer tools and nanopayments, with USDC positioned as a core asset for machine transactions.
Circle said its platform had more than 900 paid services by its second-quarter 2026 reporting and reported that 99.3 per cent of x402 agent-payment volume was settling in USDC.
AWS has also added machine payments to its cloud infrastructure. Amazon Bedrock AgentCore Payments supports payments for APIs, MCP servers and content through x402 and Stripe’s Machine Payments Protocol.
AWS provides controls including payment limits, wallet integration, transaction signing and monitoring. The service is intended to allow agents to make payments within defined financial boundaries.
Cloudflare is pursuing a similar model. Its Monetization Gateway, announced in July 2026, allows websites, datasets, APIs and MCP tools to charge through x402, with stablecoins used for settlement at launch.
Stripe introduced its Machine Payments Protocol in March 2026. MPP is designed to let agents pay businesses and other agents programmatically and supports both stablecoins and fiat payment methods.
The growing activity is not limited to cryptocurrency-focused companies.
Visa has described agentic payments as having two broad use cases: larger consumer transactions, where existing card systems can remain relevant, and very small machine-to-machine transactions, where programmable payment systems and stablecoins can be more suitable.
Visa has also expanded its own stablecoin infrastructure. In April 2026, the company reported that its stablecoin settlement programme had reached a $7 billion annualised run rate.
By September 2026, Visa said its stablecoin settlement volume had exceeded a $20 billion annualised run rate. It also reported more than 160 stablecoin-linked card programmes globally in the second quarter of its 2026 fiscal year.
Those figures represent Visa’s broader stablecoin business and should not be treated as AI-agent payment volume.
Mastercard is building another route into the market. The company launched Agent Pay for Machines in June 2026 to support high-frequency machine transactions.
Mastercard’s system can support settlement in fiat or stablecoins. The company has also expanded its settlement capabilities to include regulated stablecoins alongside intraday, weekend and holiday settlement options.
Google is focusing on the authorisation side of agent commerce.
Its Agent Payments Protocol, or AP2, is intended to establish mechanisms for authorising transactions initiated by software agents, including situations where the human is not present when the payment occurs.
Google donated AP2 to the FIDO Alliance in April 2026 and released version 0.2 with mechanisms for autonomous transactions.
The wider development shows that machine payments require more than a way to move money.
Agents also need identity, delegated authority, spending limits, transaction signing, monitoring and mechanisms for determining who is responsible when a transaction goes wrong.
Circle’s agent wallet architecture includes controls such as global spending limits, per-service limits, chain allowlists, contract allowlists and time-bounded sessions. AWS has introduced similar concepts around funded wallets and predefined payment budgets.
Security remains a significant unresolved issue.
Agents can be exposed to prompt injection, malicious services, compromised tools and other attacks that could influence spending decisions. On-chain payments also introduce questions around refunds, liability and dispute resolution.
Research published in May 2026 identified security weaknesses in x402 implementations that could result in resource leakage and payment-related problems. A separate July 2026 study examining 15 facilitators reported security-rule violations and identified risks including fraudulent free access, asset theft, denial-of-service attacks and gas abuse.
Those studies do not establish that x402 is fundamentally unsafe, but they show that autonomous payments introduce security risks that developers must address alongside the payment mechanism itself.
Another issue is the concentration of activity around USDC.
The dominance of USDC suggests that the stablecoin currently fits the requirements of machine settlement particularly well. It also creates exposure to the risks associated with a highly concentrated ecosystem, including issuer, regulatory, technical and liquidity risks.
The institutional support for x402 is also broadening. In July 2026, the Linux Foundation announced the operational launch of the x402 Foundation and the completed contribution of the protocol by Coinbase.
The foundation said 40 organisations had joined, including AWS, American Express, Circle, Cloudflare, Coinbase, Google, Mastercard, Ripple, Shopify, Solana Foundation, Stripe and Visa.
The current governing structure includes representatives from American Express, AWS, Google, Visa, Mastercard, Cloudflare, Stripe, Fiserv and the Stellar Foundation, alongside the Linux Foundation.
The development of these systems is creating a possible new form of digital commerce in which payment can happen at the same time as a software request.
An agent could pay for a single API call, a data query, a unit of computing capacity, an inference request or another digital service without requiring a human to intervene in each transaction.
That possibility is the strongest case for stablecoins in the agent economy. Their use in x402 demonstrates that a stable-value digital asset can be incorporated directly into software-driven payment flows.
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