- While the 10%-back-date-rule in Anti-Fee-Sniping is a privacy feature for some people, it is also a privacy leak for others: https://github.com/bitcoin/bitcoin/issues/26526: When fee-bumping a previously not back-date transaction, Bitcoin Core might back-date the replacement. This is fingerprint that you likely back-dated the replacement transaction. There is also https://github.com/bitcoin/bitcoin/issues/26527, which I'm not sure if it's an actual problem or not (haven't had the time to double-check). Maybe documenting some of these edge-cases in the BIP makes sense. This allows potential future/other implementations not to make similar mistakes.

- There has been a case where the trying to do Anti-Fee-Sniping 1) wasn't implemented properly in a wallet so it didn't work 2) ended up being a clear fingerprint for this wallet: https://b10c.me/observations/01-locktime-stairs/. By now, this wallet doesn't have much usage anymore (https://mainnet.observer/charts/transactions-not-enforced-locktime/) but this still shows some of it's pitfalls.

- Note that currently only around 5% of the transactions set a heigt-based time-lock: https://mainnet.observer/charts/transactions-height-based-locktime/ - growing this anonymity set might be interesting to some wallets, but currently, do don't stick out if you don't do Anti-Fee-Sniping (or use locktime).

On Tuesday, 18 August 2026 at 11:17:44 UTC+2 nervana21 wrote:

Hello all,

Anti-fee-sniping with nLockTime has been present in Bitcoin Core since
2014 and in Electrum since 2017. BIP326 assumes this nLockTime behavior
as the baseline and uses nSequence instead for some taproot spends.
However, the nLockTime rules themselves were never specified in a BIP.

https://github.com/nervana21/bips/blob/anti-fee-snipe/bip-anti-fee-sniping-with-locktime.md

The BIP draft follows Bitcoin Core's DiscourageFeeSniping and
IsCurrentForAntiFeeSniping functions. nLockTime is set to the current tip height.
With probability 10%, a uniform random integer in 0..99 is subtracted
and the result is clamped at 0. A locktime equal to the tip height
cannot be included in a remine of the tip. An older locktime chosen on
the privacy branch can. nLockTime is set to 0 during initial block
download or when the tip is more than 8 hours old. The policy is not
applied when nLockTime is already set or when any input already has a
preset nSequence. Test vectors are included.

Constructive criticism is greatly appreciated.

Cheers,
nervana21