BitcoinIII [BC3]
A Bitcoin relaunch with no compatible mining hardware and no rental hashrate market at birth
What is BitcoinIII?BitcoinIII, ticker
BC3, is a relaunch of the Bitcoin protocol, with SHA3-256t as the block hash algorithm.
The codebase is
BitcoinIII Core v29.1, based on BitcoinII Core v29.1 and Bitcoin Core v29.1. The code remains as similar as possible to Bitcoin by design. The core idea is simple:
Keep Bitcoin's consensus rules, but change the block hash / proof-of-work (PoW) algorithm to one without an existing rental hashrate market or compatible ASIC fleet at launch.BitcoinIII uses
SHA3-256t - three iterations of SHA3-256 - as its proof-of-work algorithm.
The goal is not to claim magical security from day one. No new proof-of-work chain can honestly claim that. The goal is narrower and more concrete: BC3 avoids launching into a world where a large amount of algorithm-compatible hashrate can simply be rented and redirected at the chain on short notice.
I should mention that
BC3 is not associated with BC2, despite inheriting the codebase. BC3 will likely follow upstream Bitcoin Core/Knots in the future instead.
Why BC3?Since the rise of rental hashrate markets, attacking small proof-of-work coins has become much easier.
For many algorithms, an attacker no longer needs to buy, configure, host, and operate physical mining hardware. He can simply rent hashrate for the chosen algorithm, point it at a target chain, and attempt a disruption.
That is the problem BC3 tries to avoid.
BC3 does
not share SHA-256d with Bitcoin. Bitcoin's enormous SHA-256d hashrate cannot mine BC3. Existing SHA-256d ASICs cannot mine BC3. Rental hashrate for SHA-256d cannot simply be redirected to BC3.
BC3 also does not rely on a common altcoin algorithm with a mature rental market. Its proof-of-work algorithm is
little-endian SHA3-256t over the 80-byte Bitcoin block header, and the network launched without a ready-made pool of compatible ASICs or rental hashpower.
This means that anyone who wants to mine BC3 must deliberately choose to mine BC3 with suitable CPU or GPU software. Likewise, any serious attacker must assemble, configure, coordinate, and sustain the necessary compute himself.
That is a materially higher bar than logging into a rental platform and buying temporary access to an existing hashrate market.
As mentioned, BC3 does not claim a high level of security from day one; it claims that the bar to disrupt the chain is higher. In addition, as BC3 matures, it has a smaller hill to climb than small coins whose PoW algorithm is shared with a larger coin, as it does not need to "out-hash" an existing, large pool of compatible hashrate elsewhere.
The Consensus ChangeBC3 changes only what is necessary: the block hash / proof-of-work algorithm. BitcoinIII does not use a "separate" PoW field as some chains do: the block hash algorithm
is SHA3-256t, so the PoW algorithm and block identification
both utilise SHA3-256t over the same header.
BC3 started out by using SHA-256d, but then forked to SHA3-256t for all the reasons mentioned above.
Post-fork blocks use:
SHA3_256t(header) = SHA3_256(SHA3_256(SHA3_256(header)))
The hard fork activated at
block height 30,240.
Block 30,239 was the final SHA-256d block.
Block 30,240 was the first SHA3-256t block.
At the fork height, difficulty was reset to 1:
This gave the new SHA3-256t network room to find its own hashrate instead of being trapped at an inherited SHA-256d difficulty level, with blocks 35 years apart.
The block hash algorithm is determined using
version bit 12. Pre-fork blocks do not have bit 12 set; post-fork blocks must have it set. This keeps
CBlockHeader::GetHash() an intrinsic function of the block header itself, whilst leaving the BIP320-reserved ASIC rolling bits and the top three BIP9 bits untouched. The lower 12 version bits remain available for BIP9 signalling, in case of any future soft forks.
MiningBC3 is mineable with ordinary hardware.
CPU mining: possible
GPU mining: ideal
SHA-256d ASIC mining: not compatible
Existing rental SHA-256d hashrate: not compatible
Existing BC3 SHA3-256t ASIC inventory: none at launch
An Intel i9 can produce
~10 MH/s of SHA3-256t hashrate. CUDA implementations of SHA3-256 have also been adapted for BC3, so consumer GPUs can mine the coin. Personally, my GeForce RTX 4050 is getting approx. 250 MH/s.
BC3 does not promise a long CPU-only era. This is 2026, not 2009. SHA3-256 is a NIST standard, optimised implementations exist, and open-source miners can be adapted quickly.
Instead, the claim is:
No inherited rental hashrate market.
No compatible ASIC fleet.
No large neighbouring chain whose hardware can be redirected at BC3 overnight.Every hash pointed at BC3 today comes from someone deliberately choosing to mine BC3.
Specifications| Name | BitcoinIII |
| Ticker | BC3 |
| Codebase | BitcoinIII Core v29.1, via BitcoinII Core v29.1 and Bitcoin Core v29.1 |
| Maximum Supply | 21,000,000 BC3 |
| Block Time | 10-minute target |
| Difficulty Adjustment | Every 2,016 blocks |
| Halving Interval | 210,000 blocks |
| Pre-fork PoW | SHA-256d |
| Post-fork PoW | SHA3-256t |
| Hard Fork Height | 30,240 |
| Algorithm Signal | Version bit 12 |
| Genesis / Fork nBits | 0x1d00ffff |
| Address Formats | P2PK, P2PKH, P2SH, P2WPKH, P2WSH, P2TR |
| Datacarrier Size | 83 bytes, Bitcoin Core v29.1 default |
Fair Launch StatementBitcoinIII has:
- No company
- No foundation
- No premine
- No ICO
- No special allocation
BC3 is a proof-of-work network. Coins are obtained by mining or by acquiring them from miners and holders.
The coin will be listed on
NestEx in the following days, and then
NonKYC, allowing it to be purchased and sold.
Mining Pools
ClosingBitcoinIII is an attempt to preserve the Bitcoin experience while relaunching proof-of-work under conditions where the network does not inherit the security liabilities of existing rental hashrate markets.
It is simple by design:
Bitcoin's structure.
A new proof-of-work algorithm.
No compatible ASIC fleet at birth.
No rental hashrate market.
No premine.
No foundation.
Just miners, nodes, and the chain.Discussion, criticism, miners, node operators, developers, and technically minded users are welcome.
