Stablecoins on blockchain rails are rapidly becoming the go-to payment infrastructure for AI agents, according to a new report from crypto trading firm Keyrock. The report found that AI agents settled over $73 million across approximately 176 million transactions on blockchain rails between May 2025 and April 2026, with 98.6 percent of those payments denominated in USDC. As traditional card networks struggle to accommodate the micropayment patterns of autonomous machine commerce, blockchain-based stablecoins are filling a structural gap that legacy systems were never designed to address.

Why Card Rails Fall Short for Machine Commerce

The Keyrock report highlights a fundamental mismatch between existing payment infrastructure and the requirements of AI-driven transactions. According to the findings, 76 percent of agent transactions fall below the 30-cent fee threshold that card networks typically charge per transaction, with most payments ranging between one and ten cents. For context, Visa processes approximately $14.5 trillion annually, but its fee structure was designed for human-scale purchases rather than the high-frequency, low-value exchanges that characterize machine-to-machine commerce. Stablecoins, particularly USDC issued by Circle, offer near-zero transaction costs on certain blockchain networks, making them the only viable settlement mechanism for this emerging category of economic activity.

The scale projections underscore the significance of this shift. Gartner estimates that AI agents could intermediate $15 trillion in purchases by 2028, while McKinsey projects retail agentic commerce could reach between $3 trillion and $5 trillion by 2030. If even a fraction of this volume flows through blockchain rails, the implications for stablecoin adoption and blockchain network utilization would be substantial.

Major Technology Firms Build Competing Payment Stacks

The race to build machine payment infrastructure has attracted some of the largest names in technology and finance. Coinbase launched its x402 protocol, which allows AI agents to pay directly with USDC for services such as blockchain analytics and cloud infrastructure without creating accounts or managing subscriptions. The protocol has already processed 169 million machine-native payments, serving 590,000 buyers and 100,000 sellers. Amazon Web Services entered the space in May 2026 with Bedrock AgentCore Payments, developed in partnership with Coinbase and Stripe, enabling AI agents to settle API and data feed purchases in USDC with approximately 200-millisecond settlement times.

Google developed its Agent Payments Protocol, known as AP2, in collaboration with over 60 organizations including Mastercard, PayPal, and American Express. The protocol was further extended through an A2A x402 integration with Coinbase, MetaMask, and the Ethereum Foundation to support stablecoin transactions. Stripe has also entered the arena with its Machine Payments Protocol on the Tempo blockchain, while Visa is developing tokenized credentials for AI-driven commerce. The breadth of corporate involvement suggests that machine payments represent a category that major incumbents view as strategically important.

Stablecoin Volumes Reflect Broader Adoption Trends

The growth in machine payments coincides with a broader acceleration in stablecoin adoption across business and institutional channels. Business-to-business stablecoin payments grew from under $100 million monthly in early 2023 to over $6 billion monthly by mid-2025, according to industry data. USDC alone has processed over $55 trillion in lifetime volume as of January 2026, while Visa settled $4.5 billion annualized in stablecoins during the same period. In Latin America, 71 percent of firms now use stablecoins for cross-border transactions, according to a Fireblocks survey conducted in 2025.

Risks and Regulatory Uncertainty

Despite the momentum, significant questions remain unresolved. The regulatory landscape for autonomous machine payments is largely uncharted territory. MiCA in Europe, the GENIUS Act in the United States, and the EU AI Act are all expected to take effect around mid-2026, yet none of these frameworks directly address autonomous machine-to-machine transactions or the complex liability questions that arise when AI agents execute financial operations without human oversight. Issues around agent identity verification, dispute resolution, and consumer protection in fully automated payment flows remain open.

There are also concentration risks to consider. With 98.6 percent of machine payments currently settling in a single stablecoin, the ecosystem’s dependence on USDC and its issuer Circle represents a potential single point of failure. Whether competing stablecoins or alternative settlement mechanisms will emerge to diversify this risk remains an open question as the market matures.

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