Bitcoin BLAKE2b (XBT / BTCB2)XBT / BTCB2
The 2026 fork that grew out of Luke Dashjr's BIP-110 anti-spam soft fork and replaced SHA-256d with BLAKE2b. Sold as XBT on some venues.
Vlad's verdict in the magazine: the youngest and most volatile chain in the issue, and the only one that began as an attempt to make Bitcoin smaller. The XBT ticker is an operational hazard because Kraken has long used XBT for Bitcoin itself.[2][5]
Contents
From soft fork to hard fork
The chain began as BIP-110, a soft fork to restrict arbitrary data on Bitcoin[1]. Activation split the chain at block 961,632 on 8 August 2026, the first block of BIP-110's mandatory signalling period; the SHA-256d side then produced only eight blocks in 22 days[2]. Bob Summerwill described the minority chain grinding to a halt on S17 E42[3].
New proof of work
The project then switched proof of work from SHA-256d to BLAKE2b; the first BLAKE2b block was 961,640 on 30 August 2026[4]. The project's developer page says it is not BIP-110 itself, which was a soft fork, but a hard fork that changed the proof of work so existing SHA-256d miners cannot produce valid blocks[4]. The algorithm was chosen by a lottery using the last hex digits of Testnet4 blocks[2].
Temporary data limits
Reduced-data rules and an 800,000 weight unit cap (about 300 kB) apply until the previous block's median time past reaches 1 September 2027[4].
Names and the XBT problem
The same asset trades as XBT, BTCB2 and BIP110 on different small venues[2]. XBT has long been used for Bitcoin itself on platforms such as Kraken, so a media advisory asked outlets to identify the fork by network, not ticker[5].
People
Luke Dashjr, maintainer of Bitcoin Knots, is credited on BIP-110 and authored the BLAKE2b header, the activation headline and the coinbase maturity rule[2]. On S17 E17, months before the split, Vlad predicted a Knots fork would let the market price BIP-110's ideas[6].
References
- primaryBIP-110 specification [archived]
- btkBitcoin BLAKE2b: The Fork That Fired the Miners (BTCTKVR: Forks!) [archived]
- episodeS17 E42: Bob Summerwill — the BIP-110 chain ground to a halt▶ listen at 38:26timestamp transcript-derived, pending a listen [archived]
- primarybitcoin-blake2b.org, “Bitcoin for developers” [archived]
- secondaryBitcoin Marketing Department, BLAKE2b fork media advisory (XBT naming) [archived]
- episodeS17 E17: Lukas Hozda on BIP-110 — Vlad on a possible Knots/BIP-110 fork▶ listen at 1:18:41timestamp transcript-derived, pending a listen [archived]
- primaryBitcoin Knots 29.4.1 release files [archived]