Sparrow 2.5.5 built to follow the BLAKE2b chain, where Bitcoin's mainnet proof of work changed at block 961640 on 30 August 2026.
This build only talks to a server on that chain. It reads the fork point a server reports in server.features and refuses one that disagrees, or that does not report a fork at all. That check exists because the two mainnet chains share a genesis block, a network name and an address format, so without it a wallet connected to the wrong server syncs perfectly well and shows balances for a chain you did not choose.
Pair it with Electrs Pruned, which reports the fork point. An ordinary Electrum server will be refused.
What is new in this release
This picks up upstream Sparrow 2.5.5 and the drongo changes that came with it. Nothing in the BLAKE2b support changed, and nothing upstream changed touched it: the chain code, the header store and the server checks are the same as in 2.5.4.
From upstream: signatures are shown for a signed transaction opened offline, or when the server cannot return every input; an entered https scheme is kept when configuring a Bitcoin Core server; a Bitcoin Core RPC error that carries no result is reported rather than failing on a null response; and silent payment codes sharing a scan key are sorted ascending for BIP375 ordering.
If you are running 2.5.4 there is no urgency here. Your wallets, settings and header store carry over untouched.
Installing alongside upstream Sparrow
Both can be installed and run on the same computer. This build keeps its own wallets, settings and header store, under ~/.sparrowblake2b on Linux and macOS and %APPDATA%\Sparrowblake2b on Windows. Nothing is shared with an existing Sparrow installation, and installing this does not touch one.
On macOS the application is Sparrow BLAKE2b.app with its own bundle identifier, so it sits beside Sparrow.app rather than replacing it.
macOS: the first launch is blocked
These disk images are not signed or notarized. macOS will refuse to open the application the first time and say it is damaged or from an unidentified developer. It is neither; it is unsigned.
To open it, right-click the application in Finder and choose Open, then confirm. If that does not work:
xattr -d com.apple.quarantine "/Applications/Sparrow BLAKE2b.app"
You only need to do this once.
Verifying what you downloaded
gpg --verify SHA256SUMS.asc SHA256SUMS
sha256sum -c SHA256SUMS
What changed from upstream Sparrow
Block headers on this chain are 164 bytes rather than 80 above the fork, and both lengths appear in one chain. The header format, the block hash, the on-disk store and the Electrum response handling all read the length rather than assuming it.
The difficulty rule models the one-off target change at the fork. The target moves 2^22 easier at block 961640, part way through a difficulty period, which the standard rule rejects.
The compiled-in mainnet checkpoints stop at height 961631, the last block the two chains share. Upstream's last checkpoint is above the split and belongs to the other chain.
Built from Sparrow 2.5.5 and drongo, with sources at paulscode/sparrow and paulscode/drongo.