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Flash Boys 2.0: Frontrunning, Transaction Reordering, and Consensus Instability in Decentralized Exchanges

Flash Boys 2.0. Philip Daian, Steven Goldfeder, Tyler Kell, Yunqi Li, Xueyuan Zhao, Iddo Bentov, Lorenz Breidenbach and Ari Juels.

A measurement paper. Miners and bots reorder and insert transactions around DEX trades. The authors name miner-extractable value and show priority gas auctions. It is not a trading manual, and it is not a claim that any strategy here is available or profitable now.

Flash Boys 2.0 measures how public Ethereum transactions were reordered around early DEX trades. Whoever can order the block can take value from the trade. If that value exceeds the block reward, the chain's own consensus can be bid for.

The five-minute read

The mempool is a broadcast of intent

A transaction sitting in public view is an option on its own execution. A searcher can buy before it and sell after it, or bid to land next to it. The paper records that auction in gas prices.

The producer is the auctioneer

Miners, in the 2019 setting, choose inclusion and order. The profit is not a fee the protocol printed. It is the difference a reorder can extract from users who already submitted.

Time-bandit is the consensus claim

If reordering old blocks pays more than the reward for extending the tip, a rational miner rewrites history. The paper's warning is about consensus stability, not about a particular bot.

This is not a how-to

The study names the incentive. It does not specify a sandwich, a bundle format, or a current profit. Those details change, and copying them is not what this library is for.

One action, walked through

  1. A user broadcasts a DEX trade with a public slippage tolerance.
  2. Observers see it before it is mined.
  3. Searchers bid, by gas or by direct payment, to place their transactions around it.
  4. The block producer includes the winning order.
  5. The user's execution price is worse than the price they would have had without the insertion, by up to the slippage they allowed.

The argument, unpacked

MEV is a property of a transparent ordered log

Any chain that publishes intents and then lets one party order them creates the same shape of profit. Hiding the intent, constraining the order, or auctioning the right to order are different responses. The paper does not pick a product. It shows why doing nothing is a design.

Private order flow does not delete the incentive

Later private mempools and builder auctions changed who sees the transaction and who gets paid. They did not make reordering worthless. A design that says MEV is solved has to say which of those actors still exists.

What has to be true

  • The measurements are about the exchanges and the period the paper studied. They are not a current volume figure.
  • Users set slippage. A trade with zero slippage fails instead of being robbed. The loss moves from price to failure.
  • Block producers can order transactions. A protocol that removes that discretion removes this specific auction.
  • The DEX's price is a function of order. A constant-product pool is. An order book is too, with a different shape.

What happened after the paper

The acronym MEV stuck. Searchers, builders, and proposer-builder separation grew up around the incentive the paper measured. None of that later market is in the 2019 data. The durable claim is the time-bandit: value that can be taken by reordering can become a bid for the chain itself. Cite the paper for that, not for a trading strategy.

What to check before you use the idea

  • Are intents public before they execute?
  • Who chooses transaction order, and can that right be sold?
  • Is the extractable value comparable to the protocol reward?
  • What does the user allow: slippage, a deadline, or a revert?

Terms

Extractable value
What a block producer can gain by including, excluding, or reordering transactions, beyond the protocol reward.
Priority gas auction
Searchers bidding in transaction fees to land in a specific position relative to a victim trade.

The problem the paper names

Public mempools tell the world your trade before it is final. Whoever orders the block can trade ahead of it. The paper asks how large that effect already was on early Ethereum DEXs, and whether the extractable value can exceed the block reward.

What the design proposes

  • Observe pending transactions and the gas auctions around DEX calls.
  • Define extractable value as what a block producer can take by including, excluding, or reordering.
  • A time-bandit incentive if stealing that value pays more than producing blocks honestly.

How the mechanism is specified

  • A priority gas auction is bots bidding in gas to land immediately before or after a victim transaction.
  • The block producer, or a searcher paying the producer, captures the difference.
  • If that prize dominates the protocol reward, consensus itself is what gets bid for.

What this page does not treat as proven

  • Figures from 2019 are not current market sizes. The mechanism is the part that aged into a category.
  • This page does not describe how to front-run, sandwich, or auction order flow.
  • Private mempools and proposer-builder separation came later. They change who sees the order. They do not delete the incentive.

Why a venture studio still reads it

Treat MEV as a property of a public ordered log, not as a product. A design that publishes intents before they execute has to say who is allowed to reorder them.

This is Blockchain Lab's reading of a public design paper. It is not the paper, not a copy of it, and not an offer of tokens, equity, custody or a partnership. Later network behaviour can diverge from the text. Nothing here is investment, legal or technical advice.

Research status: Design paper. Last reviewed: 1 October 2026. This is a reading of a public paper, not investment, legal or security advice.