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Although I've broadcasted many transactions via testnet with RBF opted-in ( --rbf true), yet, given different incentives present among the miners of the testnet and of the mainnet, my experience so far does not seem very helpful when it comes to grasping firmly how RBF works in Electrum. So far I've always broadcast them with 1 sat/byte. I most cases they were picked up by miners with this fee. A couple of times I noticed a slight discrepancy between the fee that I did broadcast (always 1 sat/byte) and the fee (1.2-1.3 sat/byte) that was shown in the blockchain explorer. Such minor discrepancies suggest to me that Electrum somehow automates the process of bumping the fee up when needed.

Does Electrum handle incrementing the fee for me or do I have to manually bump the fee up? If the latter is the case, can the fee bumping be done from the terminal (i.e. without GUI)? If the logic of the wallet automates the RBF process, how does it look like exactly? How many blocks does it wait until it increments the fee? By what factor is the fee increased? I have not found any information that would answer my questions in Electrum's documentation.

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    When you write "broadcast", I think you're actually referring to your transaction building instructions. I.e. you instructed your wallet to build with 1 sat/vB, but what was broadcast had a slightly higher feerate. I'm asking about that, because it could otherwise be understood that you first broadcast a transaction with the lower fee, but then saw an updated variant of the transaction later on the network, but I don't think the latter is what you mean.
    – Murch
    Jul 8 at 16:14
  • @Murch When I wrote Although I've broadcasted many transactions via testnet with RBF opted-in ( --rbf true) I meant that I broadcasted to the mempool, i.e. executed two commands: first electrum payto with --rbf true flag and then, after getting a long string of numbers in the output, electrum broadcast long_string_of_numbers. When I referred to the fee (1.2-1.3 sat/byte) that was shown in the blockchain explorer. I meant here the tx fee shown on some Bitcoin explorers, after being the tx have been confirmed. Jul 8 at 17:07
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    Yeah, I guess it's just a small terminology nit: we would usually describe the first step as the transaction building and the second step where you submit the transaction to the network as the broadcast. The feerate is decided in the "payto" step where the transaction is built. Transactions are immutable after built, so the second step just allows you to either broadcast or refrain from broadcasting a fixed transaction.
    – Murch
    Jul 8 at 17:52
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A couple of times I noticed a slight discrepancy between the fee that I did broadcast (always 1 sat/byte) and the fee (1.2-1.3 sat/byte) that was shown in the blockchain explorer. Such minor discrepancies suggest to me that Electrum somehow automates the process of bumping the fee up when needed.

Most of the times its above 1 sat/byte (it should be sat/vbyte instead of sat/byte but thats unrelated to question) and you can notice this even in Electrum before broadcasting transaction on top-left in the below screenshot:

fee-rate-electrum

If you try different values in fee rate and fee, it will either be below relay fee so not broadcasted or above 1 sat/byte.

Reason:

rounding

This rounding can be disabled from preferences:

preferences

Now you can use 1 sat/byte fee rate:

1-sat-fee-rate

Does Electrum handle incrementing the fee for me or do I have to manually bump the fee up?

If a transaction has RBF enabled it can be replaced with another transaction that uses higher fee rate and fee. Right click on any transaction that is not confirmed yet and click on 'increase fee':

RBF

Click on OK, sign and broadcast the replacement transaction: 4df6cc117882570b635bf08c28152e5985885227c19ac4cb337532241fdfd087

can the fee bumping be done from the terminal [...]?

Yes bumpfee command can be used which was added in https://github.com/spesmilo/electrum/pull/7438

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