Coinbase marked its Business unit's first anniversary this week by flipping on a feature that lets any of its roughly 5,000 business customers accept payments directly from AI agents, no separate integration required. The mechanism is x402, the payment standard Coinbase built and then handed to a Linux Foundation-governed foundation, which repurposes the long-dormant HTTP 402 "Payment Required" status code into a working machine payment protocol. The flow is mechanical and auditable: if payment is required, the server responds with HTTP 402 and includes payment instructions in a structured header specifying the price, accepted tokens, recipient address, and network. The agent doesn't just send money and hope — it reads the payment instructions, signs a stablecoin transaction, attaches the proof, and retries the request, and the server verifies the payment before returning the data. That signed, attached proof is the load-bearing part: every transaction carries cryptographic evidence that can be checked independently of either party's say-so, rather than relying on a session cookie or an after-the-fact dispute process. On the business side, the rollout removes friction entirely. The feature uses the same Coinbase Business account that companies already use to receive payments from people, and businesses can manage, reconcile, and convert agent payments without creating a separate checkout flow. Coinbase's head of Business described it plainly: "A business owner can now sell their stuff to agents online" ... "They can already sell their products, goods and services to humans today using Coinbase Business; we're just going to add a separate lane in the same product for agents." The scale is no longer speculative. Coinbase reported 69,000 active agents, 165 million transactions, and approximately $50 million in cumulative volume on x402 by late April 2026, and the average transaction size sits near $0.30 — sub-cent API metering rather than retail purchases. Coinbase also disclosed a signal about where this is headed: agent traffic surpassed human user traffic for the first time in Base documentation, meaning software is now reading Coinbase's own developer docs more than people are. What makes this notable for accountability infrastructure isn't the stablecoin rail itself — it's that the protocol builds a verifiable receipt into every single machine transaction by default, rather than bolting audit trails on after adoption. As agent commerce scales into the billions of micro-transactions, having proof-of-payment attached at the protocol layer, verified by a neutral facilitator, is what makes chargeback-free, human-out-of-the-loop commerce something a merchant can actually reconcile and trust.