Flashbots Bundles Explained: How eth_sendBundle Works

What is a Flashbots bundle?

A Flashbots bundle is a set of one or more transactions submitted together to be executed atomically and in a specified order within a single block - either the entire bundle lands as submitted, or none of it does. There is no partial execution where some transactions in the bundle succeed and others fail independently.

Bundles are submitted through the eth_sendBundle RPC method, originally introduced as part of the mev-geth project and now a standard interface supported across the broader block-builder ecosystem that grew out of it.

How eth_sendBundle provides atomicity

• A bundle specifies its transactions, their order, and the target block number it should be considered for.
• The bundle is not broadcast to the public mempool - it is sent privately to builders, which removes the front-running window that exists for ordinary, individually broadcast transactions.
• If the bundle is not included in its target block, it is generally safe to retry for a later block rather than being stuck.
• Because inclusion is all-or-nothing, a bundle can safely combine dependent transactions - for example, a token deployment and an opening buy - without the risk of one succeeding while the other fails or gets front-run in between.

MEV-Boost and the builder market

MEV-Boost is the middleware that lets Ethereum validators source blocks from a competitive market of builders rather than constructing every block entirely themselves. Under this proposer-builder separation model, builders assemble candidate blocks - incorporating bundles like the ones described above - and submit them through relays to validators, who accept the most valuable block offered without seeing its full contents in advance.

This market structure is what makes Flashbots bundles practically useful: a bundle submitted to the network of builders competes to be included in whichever block is ultimately proposed, based on how much value it adds to that block.

Why Flashbots bundles matter for a token launch

For a token launch, the core benefit is the same atomicity and privacy that makes bundles useful generally: a deployment and one or more coordinated buys can be submitted as a single bundle, executing together in one block with no public mempool exposure in between for anyone to react to.

This is a genuinely different capability from what a sequencer-based chain without a competitive relay market can offer. Robinhood Chain, for example, orders transactions strictly by arrival through a single sequencer with no public mempool and no Flashbots-style relay market - there is nothing equivalent to bundle atomically submit for same-block, no-front-running execution the way Ethereum's builder market provides.

What Flashbots bundles do not guarantee

• Inclusion in your target block is not guaranteed - a bundle competes with everything else builders are considering, and can simply not be chosen.
• A bundle does not bypass gas costs - transactions inside it are still priced and paid for according to normal Ethereum gas rules if included.
• Not every validator sources blocks through MEV-Boost, though a large majority do in practice - a bundle only reaches validators using that path.
• Using a bundle does not make a launch immune to risks unrelated to mempool front-running, such as a flawed contract or a mispriced initial buy.

FAQ

• Do I need to run my own infrastructure to submit a Flashbots bundle? No - bundles are typically submitted through a relay endpoint using the eth_sendBundle interface, without needing to run a builder or validator yourself.
• What happens if my bundle isn't included? It generally is not charged and can be resubmitted targeting a later block, since it was never broadcast publicly or partially executed.
• Is a Flashbots bundle the same as a bundler tool like TokenBundle? No - a bundler tool coordinates wallets and prepares a launch plan; a Flashbots bundle is one possible execution method that plan can be submitted through on Ethereum specifically.
• Does Robinhood Chain support Flashbots-style bundles? No - Robinhood Chain has a single sequencer with no public mempool and no equivalent relay/builder market, so this specific mechanism is Ethereum-specific.