What BTC BLAKE2b is.

Fork height

961,640

Activated

30 Aug 2026

Proof of work

BLAKE2b

Node software

Bitcoin Knots

Bitcoin proves a block by hashing its header twice with SHA-256 until the result falls below a target. This chain replaces that with BLAKE2b over a restructured 164-byte header. The rules that matter to a holder — the 21 million limit, the halving schedule, the addresses, the signatures — are untouched. What changed is who can compete to produce blocks.

SHA-256 mining has been the preserve of purpose-built machines for over a decade, because the function is cheap in silicon and ruinously expensive everywhere else. BLAKE2b moves that line. It is fast enough on an ordinary processor that a laptop can produce valid work — not competitively against a warehouse, but genuinely, and measurably: one core computes about 6.66 million BLAKE2b hashes a second.

There is a second, temporary change. Blocks are capped at 800,000 weight units instead of the usual 4,000,000, a restriction that expires on 1 September 2027. It is why blocks on this chain are smaller than you might expect.

This is not the SHA-256 chain. That chain carried on and is entirely unaffected by any of this. From block 961,640 there are two chains that share one past, and a coin on one is not a coin on the other.

Because the history is shared, an address that held BTC before the fork exists on both chains. That is exactly why you should never point mining payouts, or anything else, at an address holding SHA-256 BTC. Create a fresh wallet for this chain and use an address that has only ever existed here. It costs nothing and it removes a whole category of mistake.

Two things follow from the algorithm. The first is that Sia-generation ASICs — built for BLAKE2b when Siacoin used it — mine this chain on stock firmware, with no reflash and no patched software. The second is that SHA-256 ASICs cannot mine it at all; an Antminer S19 will connect, look busy, and have every share rejected. Which machines work, and how often each lands a share, is set out on the hardware page.

Mining needs three values and no account: a stratum URL, your payout address as the worker name, and any password. On this pool the address is the account — there is nothing to register and no password to lose.

1. 01

   A fresh address

   Create a wallet for this chain and copy a receiving address. Never reuse one that holds coins on the other side of the split.

2. 02

   The port for your hardware

   3333 for a BLAKE2b ASIC, 4444 for an FPGA or GPU, 5555 for a CPU. Add one to each for solo mining.

3. 03

   Three fields

   URL, worker, password — then watch for accepted shares. Your page appears under Miners within a minute or two.

The setup page has the exact values, and the published protocol specification has the wire format down to the byte if you are writing a miner yourself.

Is this the same as SHA-256 Bitcoin?

No. They share every block before 961,640 and nothing after it. The SHA-256 chain continues on its own; this one runs separately, with its own difficulty, blocks and coins.

Why change the proof of work at all?

To move mining back within reach of general hardware. BLAKE2b is cheap enough on a normal processor that a computer can produce valid work, which SHA-256 has not allowed for years.

Do I need a new wallet?

Yes, and it matters. Use an address created for this chain only. An address that holds BTC exists on both chains, and mixing them is how people lose coins.

What software does the node run?

Bitcoin Knots, version 29.4.2 or newer. A node has to be one that follows the fork; an unmodified Bitcoin Core node stays on the SHA-256 chain and will not see this chain's blocks as valid. From block 973,440 the version matters for mining as well: an older node still accepts spends the network no longer does, so anyone mining on one builds invalid blocks.

Where can I read the specification?

For the chain itself, bitcoin-blake2b.org. For the mining protocol as this pool speaks it — every field, its length and its byte order, with a reference implementation and a test vector — see stratum-protocol.md.

What is BTC BLAKE2b?

It is the chain that Bitcoin Knots follows after the BLAKE2b hardfork, which activated at block 961,640 on 30 August 2026. It shares every block of Bitcoin's history before that height and differs after it in one decisive way: a block is proved with BLAKE2b instead of SHA-256.

At what height did the BLAKE2b fork activate?

Block 961,640, on 30 August 2026. Before that height the two are the same chain; after it they are two chains with the same history.

Why did the proof of work change to BLAKE2b?

BLAKE2b is far cheaper to compute than SHA-256 on general hardware, so ordinary computers and graphics cards can take part in mining rather than only purpose-built SHA-256 machines. As a side effect, the Sia-generation ASICs built for BLAKE2b mine the chain on stock firmware.

How do I mine BTC BLAKE2b?

Point a BLAKE2b miner at a pool on this chain with three values: the stratum URL, your payout address as the worker name and any password. On B2Pool the ports are 3333 for ASICs, 4444 for FPGAs and GPUs and 5555 for CPUs, with the same ports plus one for solo mining.

What is RDTS and the 800,000 weight unit limit?

Alongside the proof-of-work change, blocks are temporarily capped at 800,000 weight units instead of 4,000,000. The cap expires on 1 September 2027, after which the ordinary limit returns.