AltFee (Gas Abstraction)
Overview
Every blockchain transaction requires gas paid in the chain's native token (typically ETH). This creates a critical UX barrier: users and agents must acquire, hold, and manage ETH balances solely for transaction fees. For payment use cases, this is impractical — imagine requiring merchants to hold a separate "fee currency" just to accept credit cards.
AltFee is Morph's native gas abstraction mechanism. It allows any transaction to pay gas fees in approved ERC-20 tokens (e.g., USDC, USDT0, BGB) instead of ETH.
How It Works
- The user constructs a standard EVM transaction.
- Instead of submitting a Type-2 (EIP-1559) transaction, the client submits a Type-0x7F transaction — Morph's custom AltFee transaction type.
- The transaction includes a
token_idfield specifying which token to use for gas. - Morph's sequencer validates the transaction, deducts gas fees from the user's token balance, and executes the transaction.
- From the user's perspective, the experience is identical to a normal transaction — except no ETH is required.
Supported Tokens
| Token | Contract Address | Token ID |
|---|---|---|
| USDC | 0xe34c91815d7fc18A9e2148bcD4241d0a5848b693 | — |
| BGB | 0x389C08Bc23A7317000a1FD76c7c5B0cb0b4640b5 | 4 |
| USDT0 | 0xe7cd86e13AC4309349F30B3435a9d337750fC82D | — |
Key Properties
- Zero ETH required — Users and agents can operate entirely in stablecoins.
- Native protocol support — AltFee is implemented at the sequencer level, not as a smart contract wrapper. This means lower gas overhead and higher reliability than relayer-based solutions (e.g., ERC-4337 paymasters).
- Transparent pricing — Gas costs are denominated in the chosen token at real-time oracle rates.
- Composable — AltFee works with all Morph Rails services. x402 payments, DEX swaps, token transfers — all can use AltFee.
Competitive Advantage
This is a critical differentiator versus Base and other L2s. On Base, agents must acquire and manage ETH for gas. On Morph, an agent funded with only USDC can operate indefinitely — a fundamentally simpler operational model for autonomous systems.
For the full AltFee technical specification including transaction signing procedures and protocol architecture, see the AltFeeTx Technical Specification.