They are not competing. They are building different floors of the same building. And the most important floor does not exist yet.

The limitation is also clear. Crypto only. USDC only. No fiat path.

x402 is USDC only?

Officially there are more (https://docs.x402.org/core-concepts/network-and-token-support), but, for example, the Coinbase docs only mention USDC.

In x402, USDC is the default payment token on most EVM networks. When you use a price string like $0.01, the system automatically infers USDC. It's preferred because it implements EIP-3009, enabling single-signature gasless transfers with no approval step needed."

No, x402 is not limited to USDC only. USDC was the primary token initially supported through the EIP-3009 standard, recent updates have expanded x402 to support all ERC-20 tokens. In fact x402 is token-agnostic.