Re: [bitcoindev] [BIP Draft] 24 bits for nVersion nonce space instead of 16

Anthony Towns
2026-03-28T13:54:37Z

On Thu, Feb 26, 2026 at 05:12:03PM -0500, Matt Corallo wrote:
> ==Specification==
> 24 bits from the block header nVersion field, starting from 5 and ending at
> 28 inclusive (0x1fffffe0), are reserved for nonce use and removed from BIP8
> and BIP9 specifications. A mask of 0xe000001f should be applied to nVersion
> bits so bits 5-28 inclusive will be ignored for soft-fork signalling and
> unknown soft-fork warnings.

This conflicts with the proposed use of bit 5 for signalling CTV activation
over the next twelve months mentioned at:

* https://groups.google.com/g/bitcoindev/c/HC2bn4QOR-M/m/TF8qJidzAAAJ
* https://delvingbitcoin.org/t/bip-119-ctv-activation-client/2242
* https://github.com/ctv-activation/activation-client/blob/06ddbdf01bc8ce181b01c7497010bff74c2b79c6/src/kernel/chainparams.cpp#L121-L127

I don't think there's any meaningful support for that activation proposal,
but thought it was worth pointing out for completeness.

BIP110 is currently signalling via bit 4 until block 963648; LNHANCE
is possibly signalling on bit 3 between May last year and Jan 2028.

Previously, CSV signalled on bit 0, segwit on bit 1, segwit reduced
threshold (bip 91) on bit 4, and taproot on bit 2.

Cheers,
aj

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