Cross-exchange arbitrage relies on predictable, low-latency execution and low transaction failure costs. Miner Extractable Value MEV and priority gas auctions historically made that difficult: competing searchers bid up fees and reorder transactions, increasing costs and the risk of being front-run. Flashbots introduced a private bundle relay and auction mechanism to route signed transaction bundles directly to block producers, bypassing the public mempool and the open priority gas auction.
How the relay changes execution
The Flashbots team at Flashbots describes a workflow where arbitrageurs submit signed bundles that include both the arbitrage transaction and a compensating fee, which miners can include as a block-level decision. This reduces exposure to public mempool observation and lowers the incidence of failed, repeatedly rebroadcast transactions. Earlier academic work by Philip Daian and Ari Juels at Cornell Tech documented the harms of public transaction ordering and motivated private-relay approaches. The immediate effect for cross-exchange arbitrageurs is greater certainty of inclusion and fewer wasted gas expenditures when a trade is beaten on-chain.
Causes of improved profitability and remaining limits
Improved profitability stems from two mechanisms. First, reduced competition in the mempool and avoidance of costly fee escalation means arbitrageurs spend less on transaction fees. Second, the ability to bundle and atomically execute complex multi-step arbitrages reduces slippage and execution risk. However, these gains are conditional: arbitrageurs still need low-latency price feeds, capital, and sophisticated off-chain infrastructure to detect and construct profitable bundles. Flashbots reduces one class of execution risk but does not eliminate on-chain latency, off-chain counterparty delays, or cross-venue withdrawal times that can spoil arbitrage.
Consequences extend beyond individual profitability. The Flashbots team at Flashbots documents a shift in where MEV is captured, concentrating power with relayers and miners and raising centralization concerns. Smaller participants may be excluded if they cannot afford the tooling or relationships to access bundle submission channels. There are also territorial and environmental nuances: in regions where regulatory or exchange connectivity is constrained, private-relay advantages can be muted; and fewer repeated failed transactions can reduce wasted compute and fee-related environmental cost marginally.
In summary, private-relay systems pioneered by Flashbots can improve profitability for technically equipped cross-exchange arbitrageurs by reducing mempool competition and failed-tx costs, while also shifting and concentrating economic rents and imposing new infrastructural and access barriers.