Go-Ethereum – How Legacy Transactions are Handled After EIP1559 Update

Yes, the transaction format for EIP-1559 is different. The current transaction format (now called legacy transactions) will still work, but will result in you always overpaying for transactions.

Legacy transactions have a gas price, whereas EIP-1559 transactions have a priority fee and max fee. The max fee is how much you are willing to pay in total for your transaction (so base fee and the priority fee combined). If you send a legacy transaction, the specified gas price will be used for both the priority fee and max fee. This will result in you paying the full difference between the base fee and the set gas price to the miner, since you didn't set a lower priority fee.

How you get the priority fee will also likely change, and you shouldn't need an API like ETH Gas Station for this anymore, but how this should be calculated will probably wait until after the launch of EIP-1559.

Web3.py appears to support EIP-1559 already, and will try to determine the best max fee and priority fee: https://github.com/ethereum/web3.py/pull/2055

Let's quickly understand how the fee is changed in EIP-1159.

1. Base Fee: Base fee is determined by the network itself.
2. Max Priority Fee: Optional. Determined by the user and paid directly to the miner.
3. Max Fee Per Gas: This is the absolute maximum fee you want to pay per unit of gas.

In the EIP-1159 transaction; we supply maxFeePerGas and maxPriorityFeePerGas. The base fee is automatically calculated by the network.

Now the base fee can increase/decrease but we have already supplied the max fee we want to pay in maxFeePerGas. So if baseFee increases in the next block, the priority fee can be adjusted to make sure the total fee never crosses the max fee.

Base Fee + Priority Fee <= Max Fee

Now about calculating the fee;

we need to get the base fee from the blockchain node and we can then decide how much max fee we want to make. Ideally, if you want your tx to be valid even after 6 blocks (assuming the base Fee increases to a maximum per block); you can use given formulae to calculate the max fee.

Max Fee = (2 * base fee) + Priority fee

So in terms of how do we get each field:

baseFee = await (web3.eth.getBlock("pending")).baseFeePerGas
priorityFee = choose yourself
MaxFee = (2 * baseFee) + priorityFee