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How To Bridge Coins Back From Base To Ethereum: A Comprehensive Guide

Rene Peters

July 31, 2023

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There’s been a common misconception that bridging into the Base chain is a one-way process with no way to withdraw funds. However, this is not the case. It is indeed possible to use the native withdrawal process to get your funds back on the Ethereum mainnet, albeit with a waiting period of 7 days.

Twitter user Cygaar shared a detailed guide on on how to do it. The Base chain is essentially a 1-1 fork of Optimism, which means it can leverage all the features that Optimism has. This includes a native withdrawal process that allows users to move ETH from Base back to the Ethereum mainnet. The downside is that it takes 7 days due to the challenge period.

This 7-day period is necessary because optimistic rollups need a long enough period to challenge potentially fraudulent claims. Due to this waiting period, most people opt to use third-party bridges to bridge back to the mainnet quicker. However, the native withdrawal method should always work.

The Withdrawal Process

To start the withdrawal process, users need to visit the L2StandardBridge contract on the Base chain. From there, they can choose either “withdraw” or “withdrawTo”, with the only difference being that the latter allows users to choose the destination address that receives the ETH on the mainnet.

The fields need to be filled out as follows:

1. withdraw: This is the amount of ETH you want to bridge back.
2. _l2Token: Use the value 0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000. This is the ETH token address on Base.
3. _amount: This should be the same value you used for part 1, but converted to wei.
4. _minGasLimit: Put 0
5. _extraData: Put 0x

After submitting the transaction, users should save the transaction hash for later reference.

The Role of Optimism

Optimism handles withdrawals by requiring users to post a proof to L1 that they did a withdrawal on the L2 (Base in this case). After this, the user must wait 7 days to pass so any external party has the opportunity to challenge the proof. If no challenge happens, the user can finalize their withdrawal on L1.

For Base, users can use a command-line tool for withdrawals written by the Base team. This tool requires the necessary inputs – transaction hash from above, RPC URL, and the private key of the account that withdrew.

After running this command, users will get a transaction hash. They can confirm that their proof went through by looking up this transaction hash on Etherscan (for mainnet). They’ll then have to wait 7 days before proceeding. Once this challenge period is over, they can run the second command for finalizing the withdrawal.

Withdrawing from the Base chain back to Ethereum isn’t particularly hard, but it does require some technical savviness for now. This guide is meant for people that absolutely need to bridge back right now and don’t want to wait for the official bridge UI to come out. The Optimism stack was always built with a way to bridge back from L2 to L1, they just happened to make a UI to make this process easier. This guide works for all Optimism-stack chains.