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BTC Circle's Agent Stack allows AI agents to hold USDC, follow spending rules, discover services, and make autonomous payments without manual approval.
USDC settles about 99% of x402 transaction volume, and Circle has gained a strong position as AI agents increasingly use programmable payment systems.
Circle faces competition from Coinbase, Stripe and Tether as its autonomous payment network expands into stablecoins and other digital assets.
According to Shoal Research, Circle is expanding the use of USDC as AI agents start initiating transactions. The report details Circle's Agent Stack, including wallets, Nanopayments, service discovery and developer tools, and explains how agents hold funds, follow spending rules, discover services, and make payments programmatically.
USDC dominates agency payment activities
The report states that software can trigger many agency payments without manual approval. Therefore, transaction numbers and payment volumes may better reflect the agent's activities.
USDT has approximately US$185 billion in circulation, while USDC is US$73 billion. However, USDC accounts for the majority of the combined USDC and USDT transfers, and its monthly transaction volume has increased approximately fivefold in two years.
Thereport cited x402-a mechanism that allows proxies to pay for network resources via HTTP requests. USDC was its original payment track and still settles 99% of x402 transactions to this day. Artemis data cited by Shoal Research confirms this number.
Circle adds tools for autonomous payments
In May 2026, Circle launched the Circle Agent Stack with five components: Nanopayments, Agent Wallets, Circle CLI, Agent Marketplace and Circle Skills.
Nanopayments supports transfers as low as US$0.00001, leveraging Circle Gateway to batch process authorizations and reduce settlement costs. Agent Wallets allows agents to manage funds based on predetermined spending policies.
Operators can set expenditure limits, allowed lists, prohibited lists, and allowed transaction types. Circle CLI provides developers with interfaces for wallet, CCTP, Gateway and policy management. The Agent Marketplace helps agents discover x402-compatible services, while Circle Skills provides information for AI coding tools.
Circle faces competition on payment tracks
Circle's Agent Stack is built on top of the USDC, while other companies are also developing competitive payment systems. Coinbase created x402 and operated its default settlement, as well as providing AgentKit, CDP Wallet and Base.
Stripe has developed the Tempo and Machine Payments protocols, which support stablecoins, bank cards and Bitcoin. At the same time, Tether is entering the AI payments space with its QVAC software development kit and wallet development kit.
The report also pointed out a problem with Circle's business model: Agents may increase trading activity while using their recharged wallets more frequently, leading to an increase in capital turnover, but the growth in stablecoin balances has not kept pace. Circle plans to launch the Arc main network in September 2026 and use USDC as its native Gas token.
