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I'm trying to find out the limitations of the block proposal tips paid out to validator's fee recipient on the execution layer. Like being sent to a smart contract with a fallback/receive function. What are the gas limits on these tips?

Thank you for any help!

2 Answers 2

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Builder tips you're talking about aren't received via a transaction that calls the recipient. They are just added to the balance of the fee recipient address when the block is created, your fallback/receive function wont be called by it, so the gas usage isn't a factor

You could make the recipient a contract that collects the fees and has a function you can call to execute whatever logic you need though

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  • Awesome that explains so much. Thank you!
    – Alienbyte
    Commented Sep 16, 2022 at 17:16
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Nate's answer is correct, but to expand a little further.

Validator attestations, proposals and other beacon chain rewards are added to the validator's balance. If this balance is above 32 ETH then the rewards periodically get swept to their execution layer withdrawal address (if they provided one). This is the so-called "partial withdrawal" and is not an execution layer transaction, and just ends up as a state change balance increase in the validator's withdrawal address account (and no chance to revert etc.)

Block proposer tips are also not execution layer transactions, and again are just state changes in account balance. But this time the balance increase is to the validator's fee recipient address, not the withdrawal address. Again no chance of reverting.

MEV rewards on the other hand (assuming the validator is running MEV-Boost) are slightly different. Because PBS (proposer-builder separation) is not enshrined in the ethereum protocol yet, the MEV rewards have to actually be sent as an execution layer transaction. On Etherscan for most blocks, you can see a "MEV Info" tab, which gives the MEV transaction. Basically searchers find MEV and build bundles of transactions, they submit these bundles to builders and then the builders build the blocks for the proposers running MEV-Boost to propose. The builders pay the proposers this MEV (minus a fee) usually as the lowest fee transaction in that block (they build the block so they can put their transaction anywhere). This explains (perhaps) the slightly confusing fact that MEV is still an actual transaction in the block, whereas tips are a "transactionless" state change. So although people talk about "execution layer rewards" including both MEV and tips, their mechanism of distribution is completely different, because one is enshrined in the protocol (tips) and one is not (MEV).

Finally, to your point about a smart contract with a fallback/receive function. While there is no chance of revert for validator partial withdrawals to the withdrawal address or proposer tips to the fee recipient address, the MEV transaction can still revert, because it is an actual transaction. Also just because sending doesn't revert, doesn't mean you won't still have issues.

Take for example a smart contract that has no way of withdrawing the funds. This is exactly why EigenLayer for native restaking (where the validator withdrawal address has to be set to the address of the smart contract EigenPod) warns users that:

"Ensure your fee recipient address is pointed to an address you own that is not your EigenPod. If you set the fee recipient to your EigenPod, execution layer rewards will be lost"

So while sending execution layer rewards may revert (MEV) or has no chance of reverting (proposer tips), those funds can still be stuck permanently in a smart contract if that smart contract doesn't handle withdrawals for those funds.

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