Express Relay
Express Relay is a system for routing the most contested transactions on-chain — liquidations, limit-order fills, oracle-update wraps — through an off-chain auction. Bidders compete to win the right to execute. The protocol that owns the opportunity captures the value, not the searcher who got there first.
The problem it fixes
On a normal mempool, a liquidatable position is a footrace. The first bot to land a transaction wins the bounty. In practice that bot pays nearly all of its profit back to the validator as priority fees. The lending protocol that suffered the bad debt — and the user who got liquidated — see none of it.
Express Relay says: do not race. Run a 100-millisecond sealed-bid auction off-chain. The winning bidder pays the protocol directly. Everyone else loses the auction cleanly without burning gas.
How an auction round works
- A protocol — say, a lending market — opens an opportunity on Express Relay: here is a liquidatable position, here are the parameters, the auction closes in 100ms.
- Registered searchers see the opportunity and submit sealed bids. Each bid is a complete transaction plus a value paid to the protocol.
- The auctioneer picks the highest bid, posts it on-chain through a relayer, and routes the bid amount to the protocol's receiver address.
- Losing bids never touch chain. Nobody pays gas to lose.
MEV → REV
Who Express Relay is for
- Lending markets. Liquidations are the textbook case. Aave-style protocols can route every liquidation through Express Relay and recapture the bounty.
- Perp DEXes. Insurance fund top-ups, ADL events, funding settlements — anything time-sensitive with a clear value.
- Limit-order DEXes. Each fill is a small auction. The maker gets a piece of what the taker would have paid in priority fees on a vanilla mempool.
- NFT mints. Anti-bot, anti-Sybil whitelisted auctions.
What you have to build
Integration has two halves. On-chain you add an Express Relay hook to the function you want to auction — usually a single modifier that verifies the caller is the Express Relay router and that the bid was paid. Off-chain you publish opportunities to the Express Relay service through a small SDK.
Searchers register independently. As a protocol you do not have to recruit them — Express Relay already runs a competitive bidder market.
When NOT to use it
- Transactions with no bidder competition. A 100ms auction with one bidder is just a 100ms delay.
- Cases where instant on-chain settlement is required for safety. The relay path adds latency, even if small.
- Protocols on chains Express Relay does not support yet — check the live network list before designing around it.