What is UniswapX and how does it work?

UniswapX is a trading protocol that lets people swap tokens by signing an order instead of sending a transaction themselves. Third parties called fillers compete to complete that order, using Uniswap pools, other exchanges or their own tokens. Uniswap Labs announced it on July 17, 2023, describing it as permissionless and open source under the GPL license.

What is Uniswap X, and how is it different from a normal Uniswap swap?

In a normal swap on Uniswap, your wallet sends a transaction that trades directly against a liquidity pool, and you pay the network fee. With UniswapX, you sign a message stating the tokens you will give and the range of amounts you will accept. That signed order is shared publicly, and fillers race to settle it on-chain.

The Uniswap app does not use UniswapX for every trade. Its help center says the web app offers it only above a minimum size, which depends on network costs, and routes smaller swaps, or swaps where a pool gives a better price, through Uniswap's v2, v3 and v4 pools instead.

How does UniswapX work?

Orders are filled through an auction, and the type depends on the chain. According to Uniswap's docs:

• Ethereum uses an exclusive Dutch auction. Approved quoters send firm quotes, and the most favorable one wins a short window to fill. If it backs out, the price steps down a little each block until another filler takes it.
• Arbitrum uses an open Dutch auction, where the price decays per block and any filler can act.
• Base and Unichain use a priority gas auction. Fillers bid with priority fees, and the highest bidder wins the right to fill.

A Uniswap help article gives a simple example. An order to sell 1 ETH might start at a quote of 1,000 USDC with a floor of 997. If the chosen filler fails, the offer slides toward that floor block by block.

What are UniswapX fillers?

Fillers are the businesses or bots that complete orders. Uniswap's docs say anyone can be a filler on any supported chain, while the quoters who compete for exclusive rights on Ethereum are vetted by Uniswap Labs. Fillers watch an orders feed, decide which orders are profitable and either use their own inventory or route trades through on-chain venues.

Because fillers profit from the gap between the order price and what they can get elsewhere, they are effectively the market makers of the system.

Are UniswapX swaps really gasless?

Mostly. Fillers pay the gas and fold it into the price you receive, and Uniswap says a failed swap costs the user nothing. The launch post noted that users still pay gas to approve a token through Permit2, Uniswap's approval contract, and to wrap a native token before selling it.

Uniswap also says the design limits MEV. Orders filled from a filler's own inventory cannot be sandwiched, and fillers are encouraged to use private transaction relays. As of October 2026, auction rules and supported chains can change, so check Uniswap's documentation for the current setup.