BIP-110, in alignment with the vast majority of node policy, attempted to reject use of the network for arbitrary data storage while leaving ordinary payments alone. It was a user-activated softfork: a tighter rule that old software can still follow, and that nodes could enforce even if miners did not want it. It is not this hardfork. A hardfork is a break away from abuse of the Bitcoin network. The change to the BLAKE2b algorithm exists because that softfork was blocked, and because the reason it was blocked still matters.
Industrial mining groups that answer to shareholders, not node operators, rejected the cap and kept producing blocks that used transactions most nodes would not relay as a matter of policy. Anyone can still verify that history, but following it means accepting use of the network for arbitrary data storage, which every node operator on that chain must store at their own expense and, most importantly, risk.
On August 8, 2026, nodes enforcing BIP-110 stopped accepting blocks that did not support it, while most SHA256d mining power kept producing those blocks, so the money-only rules could not activate.
This hardfork changes proof of work from the legacy SHA256d algorithm to the stronger and quantum-resistant BLAKE2b algorithm, so today's SHA256d miners cannot add blocks here. The pools that buried BIP-110 lose their lock on this chain. In that sense the hardfork "fires" the incumbent miners and lets a new market form around a ledger that is money only.
People asked for Bitcoin as money only. The mining power that refused them also stalled the chain. A new proof-of-work algorithm takes that mining power off the board.
Temporary limits on arbitrary data storage begin at the same block height as BLAKE2b. They are not a leftover BIP-110 miner-vote schedule. They apply to the new-style blocks until 1 September 2027, 00:00 UTC, using the previous block's median time past. That clock only moves forward, so the cutoff cannot flicker. While those limits are on, a block may also be no larger than about 300 kB (700,000 weight units). Coins created before the fork can still be spent under the old script rules. Continuing those limits after that date is a later choice for node operators; the BLAKE2b algorithm remains.
What this means for node operators
- If you upgrade before the hardfork: You can continue using your existing Bitcoin data directory normally. No blockchain re-download or movement of funds is required.
- If you switch from Bitcoin Core or an older Bitcoin Knots after the hardfork: That software may have followed the SHA256d chain. On startup, this release usually notices those extra blocks, walks back to the fork, and then downloads the BLAKE2b chain. That automatic walk-back is only for SHA256d blocks at or after the fork. If a BLAKE2b block itself breaks the data or size rules, you still need
-reindexto rebuild the database from blocks you already have. - A pruned node deletes old blocks to save disk space. If you waited so long that the walk-back blocks are already gone, rebuild the node and download the chain again.
- You do not need to move your bitcoin before the fork. Coins created before the fork remain spendable.
- The first BLAKE2b block includes a short agreed phrase,
blake2b_headline. Set the announced value or your node will reject that block. - After the hardfork, Bitcoin Core and older Bitcoin Knots still require SHA256d and follow a different blockchain. You need a Knots version that includes the BLAKE2b change, published at bitcoinknots.org when it is available. Source: github.com/bitcoinknots/bitcoin.
For background on BIP-110, why this hardfork is not BIP-110, frequently asked questions, and guidance for miners, wallets, exchanges, and other users, see the common questions and miners and DATUM.