ERC-6909

Uniswap v4 uses ERC-6909 to further improve gas-efficiency on token claims and redemptions.

ERC-6909 is a simple multi-token contract standard. The token standard is analogous to managing multiple ERC-20 tokens from a single smart contract - similar to ERC-1155. The major difference between ERC-6909 vs. ERC-1155 is granular approvals and the removal of inefficient safe transfer callbacks.

How it works

Instead of choosing to move tokens in/out of the PoolManager, developers can opt-in and leave the ERC-20 tokens within the PoolManager. In exchange, the PoolManager can mint them an ERC-6909 token representing their claim. In subsequent interactions requiring paying tokens, users will not need to transfer ERC-20 tokens into the PoolManager - users can simply burn some (or all) of their claim tokens they have

Doing real ERC-20 token transfers requires calls to external smart contracts - incurring gas overhead compared to internal accounting. Secondly, these external smart contracts have their own custom logic within their transfer functions - for example USDC's blocked-address list - which is a further gas overhead. Thus, minting and burning ERC-6909 tokens are more gas-efficient because they don't require external function calls and have a constant-size gas overhead regardless of the underlying ERC-20 token.

This mechanism therefore helps further reduce gas costs. All these gas cost reductions overall make pools much more competitive based on the fees they charge.

Examples

High-frequency traders / MEV bots

These users are often conducting a lot of swaps in relatively short durations of time, while staying within the Uniswap Protocol. These power-users can trade using ERC-6909 tokens for improved gas-efficiency.

Liquidity management

ERC-6909 does not only benefit swappers. For power-users that may be opening and closing liquidity positions frequently, liquidity managers can opt-in and receive their capital as ERC-6909.