> ### Bumping Fee by Deducting Fee from CTV Output
> For some reason if you still wanted to pay the fee with just the ctv ouput you could take it from the output value
> - [bump fee without extra input or child transaction: Parent Transaction on Mempool Space](https://mempool.space/signet/tx/86896275fb71d4e3b84d1edeeacb90f7c4ccf77ee3a29e66d7effff4bb0682fb)

/dev/fd0

On Wednesday, December 18, 2024 at 5:57:19 AM UTC+5:30 stutxo wrote:

Hi everyone,

I am trying to learn more about op_ctv (or its true name, op_securethebag). One thing I keep hearing is that estimating fees are potentially an issue when spending CTV transactions.

jamesob mentioned fees in his simple_ctv_valut
Because coins may remain vaulted for long periods of time, the unvault process is sensitive to changes in the fee market. Because use of OP_CTV requires precommiting to a tree of all possible specific outputs and the number of inputs, we cannot use RBF to dynamically adjust feerate of unvaulting transactions.

and rustyrussell on nostr also mentioned fees being a problem
Optimised sponsors for solving the "but how do I add fees" problem in a way that doesn't drive miner centralisation.

With v3 transactions available in bitcoin 28.0 there are a bunch of new techniques that have been enabled that we can use to hopefully solve these issues

As long as you have an output for 240 sats paying to a P2A address, such as tb1pfees9rn5nz on signet, you or anyone else will be able to bump the fees using CPFP on the anchor output.

I have some examples of these transactions here on signet

CTV spend transaction with zero fees:
https://mempool.space/signet/tx/32f4f4e6165e7f8df9b9a762e11a6ca7f16087713e0e3e42352021e6bf3800e3

P2A CPFP transaction:
https://mempool.space/signet/tx/9a3582f03b0ac39cff8ed024cf8f38e4fc4a1ee2ff216badf041bf4572c0d03b

Code used is here:
https://github.com/stutxo/simple_ctv

Is there anything I am missing here? What are the downsides of this method? Is this how most ctv scripts spends would work?

Thanks!
stu