Why x402 Doesn't Support USDT (But USDT0 Changes Everything)
Source: Dev.to
Technical limitation of USDT with x402
If you’ve explored the x402 protocol, you’ll notice it exclusively supports USDC—not USDT. The reason is entirely technical: USDT doesn’t implement the smart‑contract functions that x402 requires.
x402 payments on EVM chains rely on ERC‑3009, which enables gas‑less, signature‑based transfers. USDT’s contract only implements standard ERC‑20 functions—no transferWithAuthorization, no permit.
Feature comparison: USDT vs. USDC
| Feature | USDT | USDC |
|---|---|---|
| Standard ERC‑20 | ✅ | ✅ |
| ERC‑3009 | ❌ | ✅ |
| ERC‑2612 (permit) | ❌ | ✅ |
| Gasless transfers | ❌ | ✅ |
| x402 compatible | ❌ | ✅ |
User flow with USDC
- Click “Pay” →
- Sign in wallet →
- Instant response →
- Done
User flow with USDT
- Click “Pay” →
- Approve →
- Wait →
- Click again →
- Transfer →
- Wait →
- Done
USDT0: An omnichain upgrade
In January 2025, Tether launched USDT0, an omnichain version built on LayerZero’s OFT standard. The key difference is that USDT0 implements both ERC‑3009 and ERC‑2612.
Feature comparison: Original USDT vs. USDT0
| Feature | USDT (original) | USDT0 |
|---|---|---|
| ERC‑3009 | ❌ | ✅ |
| ERC‑2612 (permit) | ❌ | ✅ |
| Gasless transfers | ❌ | ✅ |
| x402 compatible | ❌ | ✅ (potentially) |
| Cross‑chain native | ❌ | ✅ |
USDT0 has processed over $50 billion across Ethereum, Arbitrum, Sei, HyperLiquid, Solana, and more. It also includes:
- Dual DVN Validation
- $6 M Bug Bounty
- OpenZeppelin audit
Traditional USDT remains incompatible with x402, but USDT0 opens the door to Tether‑based x402 payments. For builders, starting with USDC remains the safest path for proven compatibility.
ERC‑3009: The protocol behind x402 payments
ERC‑3009 defines the transferWithAuthorization and receiveWithAuthorization functions that enable gas‑less, signature‑based transfers. x402 leverages this to provide HTTP‑native, instant payment experiences without requiring on‑chain approval transactions.
References & further reading
- x402 Facilitators – Overview of services that enable x402 payments.
- Solana’s Authorization Mechanism – How Solana implements similar gas‑less patterns.
- x402 Developer’s Guide – Technical documentation for integrating x402 with supported tokens.
The x402 protocol’s USDC focus isn’t about preference—it’s about capability. With USDT0’s ERC‑3009 support, the future of HTTP‑native payments becomes multi‑stablecoin.