A friend asked if payments between AI agents always require crypto. The truth is, crypto isn't always necessary, and it's not impossible without it. However, native payments between AI agents are structurally easier to implement using crypto. Visa and Mastercard can support some scenarios, but they have fundamental limitations. If AI is simply paying for people, traditional payment methods are perfectly adequate. But if it's autonomous settlement between AIs, the structural advantages of crypto are very clear. The fundamental difference lies in whether it's a human-in-the-loop or a machine-native economy. Can Visa and Mastercard support agent payments? Of course, but only in an agent model, where AI simply operates payment accounts on behalf of humans. For example, AI booking your flight can use your credit card. AI automatically purchasing cloud resources can be linked to corporate cards, and AI SaaS automatic renewals can use Stripe and Visa Rails. These scenarios don't require crypto at all. However, traditional payments have structural limitations. First, the account system is identity-bound, requiring risk control, auditing, and revocable transactions—a typical human financial system. Secondly, traditional payment systems rely on bulk clearing, while credit cards use a T+1 to T+3 settlement mechanism. This involves many intermediaries and high fees, which is fine for human consumption but not fast enough for the machine economy. Furthermore, traditional payment networks do not support high-frequency, small-amount payments. The typical characteristics of AI agent economies are settlement per second, centimeter-level payments, and API-level automatic triggering. Credit cards, with their minimum fees and transaction costs, are not suitable for streaming payments. Why do people say the agent economy is naturally inclined towards crypto? It's not because of faith, but because the technological structure is indeed a good match. No identity verification is required; agents can generate their own wallets, sign their own documents, and transact independently, without account opening approvals. This is crucial for the machine economy; otherwise, it would be completely impractical for each AI agent to connect to a bank account. Secondly, there's real-time settlement. Blockchain settlement is near-instantaneous, irrevocable, and without intermediaries, while the Visa card network is essentially an IOU system (IOU system). A straightforward analogy is that Visa and Mastercard are equivalent to HTTP plus a banking system for the human internet, suitable for person-to-person and person-to-merchant transactions. Crypto Rails is essentially TCP/IP plus a native settlement layer for the machine internet, suitable for AI-to-AI automated economies and trustless environments. The most likely future form will be layered collaboration. The upper layer is fiat currency entry points, including Visa and Mastercard bank accounts, responsible for human fund sources and KYC compliance. The middle layer is stablecoin settlement, including USDC and tokenized deposits, responsible for fast settlement, API payments, and cross-platform interoperability. The bottom layer is the agent-to-agent economy, including wallets, signatures, automated payments, and machine protocols. Whether an agent payment scenario needs crypto depends on whether there are continuous autonomous transactions without human authorization. If the answer is YES, then crypto has a significant advantage; if the answer is NO, then traditional Rails is sufficient. This is why AI agent economies and tokenization are highly coupled. When tokenization turns assets into APIs, and stablecoins turn money into APIs, the next step is for AI agents to turn decision-making into APIs as well. Together, these three create programmable capital markets. Visa is a payment network within a human trust system, while crypto is a settlement layer within a machine trust system. Their relationship is one of division of labor over time, rather than one of replacement.