What Is Fractal Bitcoin? A Plain-English Guide for Miners

Fractal Bitcoin is a separate blockchain that runs a fork of Bitcoin Core with 30-second blocks and the same SHA-256 proof-of-work as Bitcoin. This article explains, in plain English, what the chain is, why only about one block in three is open to a solo miner, why its Bitcoin-identical addresses are a trap, what the reward and the September 2026 halving look like, and what the odds and node costs are.

Category: Mining and the Network · Published 2026-09-05

Editorial review complete · technical review pending · sources under review · time-sensitive: revisit periodically

Fractal Bitcoin is a separate chain, not Bitcoin

Fractal Bitcoin is a separate blockchain with its own ledger and its own coin, FB. Its node software, fractald, is a fork of Bitcoin Core — the install instructions still launch a binary called bitcoind — but it follows Fractal’s rules, not Bitcoin’s.¹ The first mined block on the chain is dated 9 September 2024.⁵

The project’s README describes Fractal as a scaling solution built from Bitcoin Core’s code.¹ Whatever you make of that framing, for a miner it is a separate chain: a Fractal block is not a Bitcoin block, FB is not BTC, and nothing that happens on Fractal moves a single satoshi on Bitcoin’s ledger. This article explains what that means for anyone who owns SHA-256 hardware and keeps hearing the name.

Why miners keep hearing about it

Two facts put Fractal in front of miners. It uses the same proof-of-work as Bitcoin — double SHA-256 — so existing Bitcoin ASICs can mine it unmodified.⁴ And its blocks are timed to arrive every 30 seconds instead of every ten minutes.⁴

The machine sees only a header and a target. What changes is who builds the work, which address is paid, which wallet can see the payment, and the odds. Only a third of those blocks are open to a solo miner; the next section explains why.

Three kinds of block: cadence mining

Fractal calls its block production cadence mining: three kinds of block compete for every height, and the design aims at one of each in every three blocks.⁴

• Permissionless proof-of-work blocks — standard SHA-256d blocks found by anyone with hashrate. This is the only kind a solo miner can find.⁴
• Merged-mined blocks — produced by Bitcoin mining pools as a by-product of their Bitcoin work, through the same auxiliary-proof-of-work mechanism Namecoin uses.⁴ On the explorer they carry the tags of pools such as AntPool, F2Pool and ViaBTC.⁵
• Indexer blocks — produced by a permissioned indexer role at difficulty 1; not open to outside miners.⁴⁵

Each kind has its own difficulty. As of 5 September 2026 the permissionless difficulty is between about 4 and 5 billion (roughly 4.5 G) and moves by ten per cent or more within a day, merged-mined difficulty is around 8 trillion, and indexer blocks stay at 1; over the recent chain the split is indeed close to a third each.⁵ The three difficulties are separate targets for separate participants, not a ranking.

For a solo miner this is the central fact of the chain. Only the permissionless third is yours to compete for, so a proof-of-work block lands about every 90 seconds on average, and the hashrate you race is the permissionless hashrate — roughly 215 PH/s as of 5 September 2026, which is what a difficulty near 4.5 G at one block per 90 seconds implies⁸ — not the Bitcoin pools’.

The addresses look like Bitcoin’s — and that is a trap

Because fractald is Bitcoin Core code, Fractal uses Bitcoin’s address formats unchanged: bc1q… (bech32, BIP-173),⁶ bc1p… (bech32m, BIP-350),⁷ and the older 1… and 3… base58 forms.¹⁶ A Fractal block reward is paid to a string that is, byte for byte, a valid Bitcoin address.⁵

That is convenient for software and dangerous for people. The same string is a valid destination on two ledgers, and each ledger knows only its own coins: FB exists only on Fractal’s ledger.⁴ So:

• Mine to an exchange’s BTC deposit address and the exchange’s Bitcoin system never sees the FB. The coins sit on Fractal at a key you do not control. In practice they are lost.
• The same goes for a payout address copied from a Bitcoin pool account, or any Bitcoin-only wallet: it shows zero because, on the ledger it reads, the balance is zero.
• The address you mine to must come from software that runs on the Fractal network and shows FB. Get that wallet before you point a miner anywhere; this mistake cannot be fixed afterwards.

The reward, and the halving at block 2,100,000

From the second block onward every Fractal block has paid a subsidy of 25 FB. The halving cycle is 2,100,000 blocks, and the total mining supply works out as 2 × 25 × 2,100,000 = 105 million FB.⁴ At 30-second blocks a cycle takes about two years, so the first halving falls in September 2026.

That first halving is also a hard fork. Fractald v0.4.0 activates at block 2,100,000 and, on top of the scheduled halving, applies an additional one-time halving from that height onward,² so the subsidy goes from 25 FB to 6.25 FB per block rather than 12.5.²⁴ Node operators must upgrade before that height; miners and mining pools, the release notes say, need not change their mining software.² As of 5 September 2026 the chain is at roughly 2,092,000 blocks,⁵ which at 30 seconds a block puts activation around 8 September 2026.

A block found after activation pays 6.25 FB, a quarter of today’s 25 FB.

What the odds look like

Solo odds on Fractal use the same arithmetic as on Bitcoin. A block takes, on average, difficulty × 2³² hashes, so expected time to a block (seconds) = difficulty × 2³² ÷ hashrate (hashes per second).⁸ Use the permissionless difficulty, the target your machine is actually trying to beat.⁴

At a proof-of-work difficulty of 4.5 G (as of 5 September 2026)⁵ the expected times are:

An expected time is an average over many independent attempts, not a countdown: a machine that has hashed for 186 days without a block is no closer to one than on day one, and a block can just as easily come in the first hour. Luck dominates on any timescale a home miner can afford, as explained in how solo-mining probability works. None of this is income advice; it describes a random process.

Two things are specific to a 30-second chain. A new job arrives every 30 seconds on average, because each block makes the previous work obsolete,⁴ so shares returned against the old job are stale: roughly 1 to 5 per cent stale on an ASIC is normal here, not a fault. And with blocks so close together, orphaned blocks — valid blocks that lose the race to be built on — are more common than on Bitcoin. Neither changes the formula.

What it costs to run a node

A solo pool runs the node for you, but many miners want their own, and Fractal’s is heavier than people expect. The README lists 2 TB of disk for a full node and 300 GB for a pruned “mining node”.¹ The prune-mode note shows where most of the 300 GB goes: about 30 GB of recent blocks plus roughly 191 GB of chain state — the unspent-output set a node keeps to validate new blocks.³

Treat 2 TB as a floor. As of 5 September 2026 the chain has more than 2.09 million blocks, and recent blocks average about 1.65 MB and roughly 8,000 transactions;⁵ the explorer puts the block data to date at about 2.3 TB, growing by several gigabytes a day. The release repository ships software and a Docker setup, not a copy of the chain, so a new node starts at the first block and validates everything since.¹ Pruning limits what the node keeps, not what it must download and process.³ And the node must be v0.4.0 or later before block 2,100,000: the release notes say an older non-mining node may keep following the chain without enforcing the new rules.²

Common misunderstandings

• “Fractal is a Bitcoin layer, so FB is a kind of BTC.” No. FB is issued by Fractal’s own subsidy schedule on Fractal’s own ledger.⁴ The BTC supply is unaffected.
• “My Bitcoin wallet will show the FB I mine.” No. A wallet that reads only the Bitcoin ledger shows zero, because on that ledger there is nothing. You need software that reads the Fractal network.
• “A block every 30 seconds means my chance comes up every 30 seconds.” No. Only about one block in three is a permissionless proof-of-work block,⁴⁵ and your chance at each is your hashrate against the permissionless hashrate, not against the clock.
• “Merged mining is solo mining Fractal for free.” Merged mining is done by Bitcoin pools that fold Fractal work into their Bitcoin work.⁴ The pool finds the block; whether any of it reaches you is that pool’s business, not the protocol’s. Solo mining Fractal means pointing your own hashrate at the permissionless blocks, during which it is not mining Bitcoin.
• “Three difficulties means the permissionless blocks are easy.” A difficulty means nothing except against the hashrate competing for that kind of block. Roughly 4.5 G against roughly 215 PH/s (as of 5 September 2026) gives the table above: days to months, not minutes.⁸

Fractal and Bitcoin, side by side

Everything above in one view. The left column is what a Bitcoin miner already knows; the right is what changes.

The resemblance is the whole point of the design, and the whole danger. The hardware, the hashing and the addresses carry over exactly. The ledger, the coin and the odds do not. Every line in that right-hand column is something that costs you money if you assume it behaves the way Bitcoin does.

Key takeaways

• Fractal Bitcoin is a separate chain running a Bitcoin Core fork: its coin, FB, is not BTC, and a Bitcoin-only wallet will never show it.
• Only permissionless proof-of-work blocks, about one block in three, are open to a solo miner; merged-mined and indexer blocks are not.
• Fractal addresses are identical to Bitcoin's, so an exchange BTC deposit address or a Bitcoin pool payout address silently loses your FB.
• The subsidy is 25 FB now and becomes 6.25 FB at block 2,100,000 (expected around 8 September 2026), when the v0.4.0 hard fork applies the scheduled halving plus a one-time extra halving.
• Expected time to a block = difficulty × 2^32 ÷ hashrate; at a 4.5 G proof-of-work difficulty a 4 TH/s miner averages about 56 days, and luck does not accumulate.
• A full node needs about 2 TB (300 GB pruned) and must download the whole chain from the first block; there is no snapshot.

Sources

1. fractald-release: README (what Fractal is, system requirements: full node 2 TB, mining node 300 GB pruned, install and Docker options) — GitHub, fractal-bitcoin
2. Fractald v0.4.0 release notes: hard fork at height 2,100,000, additional one-time halving, no miner software change — GitHub, fractal-bitcoin
3. 2025.07 Fractal Prune Mode Explained: ~300 GB in prune mode (30 GB blocks + 191 GB chainstate) — GitHub, fractal-bitcoin
4. Mining Overview: cadence mining, 30-second interval, SHA-256d, 25 FB subsidy, 2,100,000-block halving cycle, 105 million FB supply, difficulty targets — Fractal Bitcoin documentation
5. Fractal Bitcoin explorer: block heights, timestamps, per-block difficulty, block kinds and pool tags, block sizes and transaction counts — mempool.fractalbitcoin.io
6. BIP-173: Base32 address format for native v0-16 witness outputs (bech32, bc1q addresses) — Bitcoin Improvement Proposals
7. BIP-350: Bech32m format for v1+ witness addresses (bc1p addresses) — Bitcoin Improvement Proposals
8. Difficulty: expected time to a block = difficulty × 2^32 ÷ hashrate — Bitcoin Wiki

Some specific claims in this article are scheduled for further source review; citations may be expanded (see our editorial policy).

Related educational reading

• How Proof of Work Secures Bitcoin
• How Solo-Mining Probability Works
• Soft Fork vs Hard Fork, Explained