XBT replay protection, explained: what it is and how to split your coins
If you held bitcoin before August 8, 2026, you also hold the same amount of XBT, at the same addresses, with the same keys. That's what a fork does. It also creates a risk: a transaction you sign on one chain can sometimes be copied onto the other. This is called a replay, and it can move coins you didn't mean to move. Here's how it works on XBT, and how to stay safe.
Why replays happen
XBT and Bitcoin share every block up to 961,631. The chains split at block 961,632. Any coin that existed before the split exists on both chains, controlled by the same private key.
A normal Bitcoin signature doesn't say which chain it's for. So if you sign a transaction spending a pre-fork coin on Bitcoin, anyone can take that exact transaction and broadcast it on XBT, and it's valid there too. The same works in reverse. Your coins move on both chains to the same destination, whether you wanted that or not.
XBT's fix: an opt-in signature flag
XBT added a new signature flag called SIGHASH_UNIFIED (0x20). Combined with the normal "sign everything" flag, the signature type becomes 0x21 instead of 0x01. Bitcoin nodes reject that signature type, so a transaction signed this way is valid on XBT and invalid on Bitcoin. It can't be replayed.
The catch is that it's opt-in. Plain signatures are still accepted on XBT, so the protection only applies when your wallet uses the new flag. Many wallets don't.
Which wallets use it
| Wallet | Replay-protected signing |
|---|---|
| Bitcoin Knots BLAKE2b (node wallet) | Yes, from the command line and GUI |
| Sparrow BLAKE2b build | Yes |
| Shrike (Sparrow fork) | Yes, with per-wallet replay marking |
| SeedSigner, Coldcard, Trezor community firmware (privkeyio) | Yes. Unaudited, development signing keys |
| Kilombino Android wallet | Not for spends, per the community list (plain signatures) |
| Standard Bitcoin wallets and stock hardware wallet firmware | No |
Source: the community-maintained awesome-bitcoin-blake list. Check each project's own notes before you rely on it.
Who needs to worry
- You bought XBT on an exchange after Sept 1, 2026, or mined it: those coins only exist on XBT. No replay risk.
- You held bitcoin before block 961,632: you have the same coins on both chains. Split them before you spend either side.
How to split pre-fork coins safely
- Spend the XBT copy first, using a wallet that signs with unified sighash (Knots, the Sparrow BLAKE2b build, Shrike, or the community signer firmware). Send it to a new address in an XBT-only wallet.
- Wait for it to confirm on XBT. That coin has now moved on XBT only, and the transaction can't be replayed onto Bitcoin.
- Your bitcoin hasn't moved. Spend it normally on Bitcoin whenever you like.
Doing it the other way round, spending your bitcoin first with a normal wallet, can broadcast the same transaction on XBT. Test with a small amount first.
Three mistakes to avoid
- Using your bitcoin wallet's seed in an XBT app you don't trust. Pre-fork coins share keys, so that app can see and move your bitcoin too. Make a fresh seed for XBT.
- Unsplit deposits to exchanges. Some venues accept the same address format on both chains. If you send an unsplit coin, check what was credited on each side.
- "Claim your fork coins" sites. Nothing needs to be claimed. Anyone asking for your seed phrase or private key to unlock XBT is a scammer.
Want your keys offline? Our XBT cold storage guide builds a $60 SeedSigner that signs with replay protection.
For education only. Not financial or security advice. Community wallets and firmware are unaudited; test with small amounts.