AI agents are already buying and selling from each other millions of times a day, and the cryptocurrency settling those deals was decided months ago without much fanfare. The winner might surprise you, and the real battle has quietly shifted…
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Software has been transacting with other software for a year, and most people are unaware of it. By late April 2026, Coinbase reported 69,000 active agents and 165 million transactions, totaling around $50 million in cumulative volume using its x402 standard. In each of those transactions, both the buyer and seller are programs, and the average transfer amount is just a fraction of one cent.
So which cryptocurrency is used to settle these bills? The straightforward answer is that the contest for dominance concluded in the second quarter of 2026. USDC (CRYPTO:USDC) has taken the lead in the market, while XRP (CRYPTO:XRP) and Solana (CRYPTO:SOL) are now playing for different stakes.
Dominates Agent Payments #
Circle’s recent press material revealed that USDC accounts for 98.8% of agent-driven transaction volume. In a prior statement, CEO Jeremy Allaire noted that this figure had reached 99.3% for payments made by AI agents using x402 in the second quarter of 2026.
This dominance was not accidental. Circle introduced its Agent Stack in May 2026, providing developers with policy-controlled wallets, nanopayments, and a marketplace, which now supports over 900 paid services. USDC’s circulation reached $73.3 billion, and transaction volume rose 151% over the year.
Chainalysis tracked over 100 million cumulative x402 transactions on Base through the first quarter of 2026, but cautioned that much of the late-2025 surge was due to meme coin activity. Thus, the actual working market is smaller than the transaction count might imply.
Why a Stablecoin Wins in a Market of Tiny Transactions #
AI agents frequently buy data feeds, computing cycles, API calls, and model inference services, which is the technical term for requesting a trained model to generate an answer and paying for that response. Each of these services has a low price point and is often consumed thousands of times a minute.
For instance, if a service quotes an API call at $0.0004, that value must hold constant even a minute later. Only a token pegged to a currency can provide this stability, which matters before you consider factors like transaction speed or fees. A volatile asset would turn each invoice into a bet on the denominator. The x402 standard is built on the HTTP 402 Payment Required response. When a server sends back a 402, the agent reads the payment instructions, signs a stablecoin transaction, includes proof, and retries the request. Coinbase integrated stablecoin functionality into the reference implementation, settling this issue before any developer began working with the specification.
Coinbase created and open-sourced x402 in May 2025, announced a foundation with Cloudflare in September, and transferred governance to the Linux Foundation in April 2026. By that time, five deployments were operational, including Coinbase’s Agent.market, Stripe Machine Payments, CoinGecko’s paid endpoints, and the Cloudflare Agents SDK.
XRP and Solana Are Competing for Different Roles #
Within agent stacks, transactions typically default to Base for Ethereum-compatible tasks and Solana for high-throughput cases, with the actual payment still settling in USDC. Solana offers confirmations in about half a second, while Base takes roughly two seconds, both at very low gas costs. In contrast, Ethereum’s main chain is supported but is too costly for sub-dollar transactions.
So, while Solana is winning a place in this market, it functions as a routing chain rather than the asset used for payments, and those are separate business models with separate economics.
XRP took longer to enter this arena and came from a different perspective. Ripple adopted the x402 standard in June 2026 and joined the Machine Payments Protocol on September 17, allowing XRP to serve a function no other asset on its ledger can perform, which is streaming payment sessions. While RLUSD can handle one-off payments, session streaming requires a future upgrade from Ripple, which has yet to be scheduled.
| Asset | Share of Agent Volume | Role in Stack | Limit |
|---|---|---|---|
| USDC | 98.8% | Settles payments | Dependent on Circle as issuer |
| Solana | Not a settlement asset | Provides high-throughput routing | Native token price can fluctuate against invoices |
| XRP | Not measurable yet | Streams payment sessions | Joined the standard in September 2026 |
Which Coin Wins in Agent Payments? #
USDC has emerged as the clear leader, accounting for 98.8% of agent-driven volume, which leaves no meaningful competition for the settlement asset. The market resolved that question in the second quarter.
The chain underneath remains open, and that is where the next two years get decided. Circle is developing Arc to control both the infrastructure and the token, Ripple supports competing standards so the XRP Ledger stays reachable whichever way developers go, and Solana already carries a share of the routing.
A holder who assumes the fight is over the coin watches the wrong number. The one that counts is which chain the reference client selects first, because whatever it picks becomes the habit for millions of daily payments.
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