The debate is heating up. As AI agents graduate from demos to production systems that actually spend money, founders and CTOs face a fundamental choice: which payment rails should you build on?
Crypto-native protocols promise programmable money, instant settlement, and freedom from interchange fees. The vision is compelling. But when your agent needs to book a flight, spin up cloud infrastructure, or purchase SaaS seats, theory meets reality fast.
Here's the pragmatic case for building on card rails today, and why that calculus will eventually shift.
The Current Landscape
Three payment rails compete for agentic commerce:
Traditional card networks like Visa and Mastercard offer near-universal merchant acceptance. The infrastructure is battle-tested, the dispute mechanisms are established, and the regulatory framework is mature.
Stablecoins like USDC and USDT promise programmable payments with 24/7 settlement. Companies like Skyfire have built identity and payment protocols specifically for AI agents using stablecoin wallets.
The x402 protocol, launched by Coinbase in May 2025, revives the HTTP 402 Payment Required status code to enable native payments over HTTP. By December 2025, it had processed 75 million transactions. Cloudflare and Google Cloud have announced integrations.
Each approach has merit. The question is which one works for production agent deployments today.
Merchant Acceptance - The Deciding Factor
When your AI agent is tasked with "find and book the cheapest flight to Austin," it doesn't care about settlement times or interchange fees. It needs to complete the transaction. And airlines, hotels, and the overwhelming majority of merchants accept exactly one thing: card payments.
According to the 2025 Global eCommerce Payments & Fraud Report from Visa and the Merchant Risk Council, only about 10% of merchants accept cryptocurrency at checkout. That makes crypto the least accepted payment method among the surveyed merchants. Even with Stripe and Shopify announcing USDC support for millions of merchants in mid-2025, direct stablecoin acceptance remains a fraction of total ecommerce.
The math is stark. Less than 0.5% of global ecommerce transaction value flows through cryptocurrency. Meanwhile, card networks cover effectively 100% of online merchants.
For autonomous agents operating in the real economy, that gap is disqualifying.
The Comparison
| Rail | Merchant Acceptance | Dispute Mechanism | Regulatory Clarity | Works Today |
|---|---|---|---|---|
| Cards (Visa/MC) | ~100% of ecommerce | Chargebacks exist | Decades of law | Yes |
| Stablecoins | Under 1% of merchants | None standard | Uncertain | Limited |
| x402 Protocol | Nascent | None | None | No |
This table tells the whole story. Card rails aren't technically elegant, but they're universally functional.
Even Crypto-Native Players Choose Cards
The most telling signal comes from companies building at the intersection of crypto and payments. Rain, a stablecoin infrastructure provider that just raised $250 million at a $1.95 billion valuation, is a principal member of Visa. Their entire product is issuing Visa cards backed by on-chain stablecoin wallets.
Think about that. A company that raised hundreds of millions to advance stablecoin payments chose to wrap those stablecoins in Visa cards rather than push direct merchant acceptance.
Rain's approach lets businesses hold self-custodied stablecoins while still transacting at any merchant that accepts Visa. They've processed payments in over 150 countries. That reach would be impossible with native stablecoin rails.
Skyfire tells a similar story. Their KYAPay protocol supports both USDC payments and tokenized credit/debit cards. The system is designed for AI agents, with programmatic wallets and Know Your Agent (KYA) identity. But when merchants don't accept stablecoins directly, agents need card rails to complete transactions.
The pattern is clear: even crypto-native infrastructure is bridging to cards, not replacing them.
The Bull Case for Crypto Rails
None of this means stablecoins and protocols like x402 are wrong-headed. The theoretical advantages are real:
Programmability. Smart contracts can encode complex payment logic that card networks can't match. Escrow, milestone-based payments, and conditional transfers become native primitives.
Settlement speed. Cards settle in days. On-chain stablecoins settle in seconds or minutes. For high-frequency agent transactions, that difference compounds.
Cost structure. Interchange fees typically run 1.5-3% per transaction. Stablecoin transfers cost a fraction of that. Coinbase's x402 facilitator offers fee-free USDC payments on Base.
24/7 availability. Blockchain networks don't observe banking hours or holidays. Agents can transact at any time without settlement delays.
Native machine interfaces. HTTP 402 responses with payment instructions are more natural for software than OAuth flows and card tokenization.
These advantages are genuine. They just don't matter if your agent can't complete transactions at most merchants.
When Crypto Rails Will Win
The tipping point isn't technical. It's about merchant adoption.
Several forces are pushing in that direction. The x402 protocol saw 10,000% growth in activity by late 2025. Major platforms are integrating stablecoin payments. Regulatory clarity is slowly emerging in key markets.
Crypto rails will dominate agentic payments when two conditions are met:
First, major ecommerce platforms and merchant payment processors must support stablecoins as seamlessly as they support cards today. The Stripe/Shopify announcement was a step, but coverage needs to approach universality.
Second, the agent ecosystem needs standardized dispute resolution and consumer protection mechanisms for on-chain payments. Chargebacks aren't elegant, but they provide a safety net that enterprise deployments require.
We estimate this transition is 2-4 years away for mainstream use cases. For certain verticals like API marketplaces, compute providers, and digital goods, it's already viable.
The Pragmatic Path Forward
If you're building an AI agent platform today, here's the practical guidance:
Build on card rails first. Your agents need to transact with merchants who only accept cards. That's most merchants. Virtual cards with per-agent, per-workflow controls give you the programmability you need without limiting where agents can spend.
Abstract the payment layer. Design your systems so the underlying rail can change. When stablecoin acceptance reaches critical mass, you want to swap implementations without rebuilding your agent logic.
Watch the x402 ecosystem. Native HTTP payments are the long-term future for machine-to-machine commerce. Start integrating with x402-enabled services where available, particularly for API and compute procurement.
Don't dismiss crypto infrastructure. Companies like Rain and Skyfire are solving real problems around agent identity, wallet management, and programmable controls. Their architectures will inform how payments work even if the settlement layer evolves.
Conclusion
The stablecoin future is coming. Programmable money, instant settlement, and native machine interfaces will eventually transform how AI agents transact.
But "eventually" doesn't ship products. When your agent needs to book that flight to Austin, complete that SaaS purchase, or procure cloud resources, it needs payment rails that work at merchants today.
Virtual cards running on Visa and Mastercard networks aren't glamorous. They weren't designed for autonomous software agents. But they work everywhere, right now.
Build for the infrastructure that exists. Design for the infrastructure that's coming. Your agents will thank you.
Signets provides virtual cards and payment infrastructure purpose-built for AI agents. Get started with programmatic spending controls for your autonomous systems.
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