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

'Antoine Poinsot' via Bitcoin Development Mailing List
2026-02-27T16:39:49Z

Makes sense.

The current 16 bits in the header allow to serve fresh job to an ASIC only once every second up to ~280TH/s. There are nowadays ASICs that are able to perform more than 1PH/s[^0], and 8 more bits would extend that limit up to 72PH/s without nTime rolling.

This leaves 5 bits available for concurrent deployments. With upgrades becoming less frequent as Bitcoin matures, i think this is more than enough.

[^0]: https://shop.bitmain.com/product/detail?pid=00020250707194812615L4HTKEMY064E

On Thursday, February 26th, 2026 at 5:26 PM, Matt Corallo <lf-lists@mattcorallo.com> wrote:

>
> BIP: ?
> Title: 24 nVersion bits for general purpose use
> Author: Matt Corallo <bips@bluematt.me>
> Status: Draft
> Type: Specification
> Created: 2026-02-26
> License: BSD-3-Clause
> CC0-1.0
> Replaces: 320
>
>
> ==Abstract==
>
> 24 bits are reserved in the nVersion field as extra nonce space for miners, providing for additional
> hashrate with header-only mining without relying on rolling nTime more often than once per second.
>
> ==Motivation==
>
> BIP 320 defined 16 bits of nVersion as nonce space for additional nonce space. It turns out that
> this isn't enough, as some devices have started using 7 bits from nTime for extra nonce space (see
> https://github.com/stratum-mining/sv2-spec/discussions/187). Given there's limited utility in 16
> bits of nVersion space for signaling, instead here we offer 24 bits of nVersion space as extra nonce
> space.
>
> ==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.
>
> ==Rationale==
>
> Headers-only mining avoids mining devices (either ASICs or the firmware) from having to concern
> itself with the vast space of consensus logic (handling transactions, merkle trees, etc). It is
> widely deployed in ASICs, but requires a substantial number of jobs fed across an entire device,
> keeping the ASIC controller busy. Providing additional nonce space for the ASICs to roll without
> needing fresh work from the controller may simplify ASIC design somewhat, and as been apparently
> adopted in some miners by using extra space in nTime as extra nonce space. Doing so in nVersion
> instead is preferable to using nTime.
>
> ==Backwards Compatibility==
>
> Non-upgraded nodes will interpret the reserved bits of this proposal as signals for soft forks, and
> may additionally activate the warning system for unknown soft forks.
>
> At the time of writing no known soft forks are pending using any of 24 bits reserved in this BIP,
> and given that a non-trivial percentage of the hashrate is already making uses of those bits,
> future soft forks SHOULD NOT utilize those bits for activation signalling.
>
> ==Acknowledgements==
>
> Timo Hanke and Sergio Lerner for originally proposing 15-bit extra nNonce2. Btc Drak for writing BIP
> 320.
>
> ==Changelog==
>
> ==Copyright==
>
> This document is dual licensed as BSD 3-clause, and Creative Commons CC0 1.0 Universal.
>
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