What happens to P2A outputs that are never needed in the end because their user didn’t need a fee bump on their transaction? Do they just bloat the UTXO set?
Since these outputs require no witness data to be spent, presumably they will be swept once the amount of satoshis in the output is worth sweeping. The minimum amount in satoshis for P2A outputs as of Bitcoin Core 28.0 is 240 satoshis but they can also be any other larger value. This means if the going feerate for block inclusion drops to 3 sat/vbyte, it makes sense for a miner or other actor to sweep it.
I had heard that those would carry 0 value, but in fact all of them do. Is this related to the fact that usually (I think) all outputs need need to be above dust-value for transactions to be propagated? If so, how is that reconciled with the idea of having 0-value outputs (or am I just wrong about that and they’ve changed to be a minimum of the dust-value?).
Currently, all outputs have a non-0 satoshi value dust limit that’s calculated based on the script size and some other heuristics.
The original idea for “Ephemeral Anchors” was split into two separate concepts: Pay To Anchor(P2A) which is the script format, and “Ephemeral Dust”, which is the ability to have a dust output without unduly bloating the utxo set.
The latter idea is not bound to a specific output type, and is still being developed for a future Bitcoin Core release.
