Forks & controversies: how Bitcoin does (not) change

Changes to Bitcoin are often fiercely debated – sometimes to the point of a split. Here you’ll read what a fork is, which conflicts have shaped Bitcoin – each with both sides – and what to do if a split is coming.

Soft fork and hard fork: the difference

Every node checks blocks against the same consensus rules. When these rules change, that’s called a fork – as in a fork in the road:^[1]

	Soft forkGlossarySoft forkA change to the consensus rules that only tightens them. Blocks that follow the new rules remain valid for old nodes – so Bitcoin can be developed further without a chain split, as with SegWit and Taproot.In the glossary →×	Hard forkGlossaryHard forkA change to the consensus rules that allows previously invalid blocks. Old nodes reject such blocks; if not everyone goes along, two permanently separate chains emerge – and with them a new, separate currency.In the glossary →×
Rules become	stricter	looser or different
Old nodes	accept the new blocks	reject the new blocks
Lasting split	only if nodes enforce the new rules without a majority of the computing power	yes, if not everyone follows
Examples	SegWit (2017), Taproot (2021)	Bitcoin Cash (2017)

To remember it: a soft fork is like stricter house rules – anyone who follows them isn’t breaking the old ones. A hard fork allows something the old rules forbid.

Changes are proposed publicly as a BIPGlossaryBIP (Bitcoin Improvement Proposal)A publicly documented proposal for Bitcoin – for example for new rules, standards or processes. A BIP is not a decision: whether it gets used is up to users, wallets and node operators themselves.In the glossary →× (Bitcoin Improvement Proposal). A soft fork usually only activates once most miners signal readiness: TaprootGlossaryTaprootA soft fork from November 2021 that introduced Schnorr signatures and more flexible spending conditions. Complex arrangements such as multisig can look like a simple payment. Taproot addresses start with bc1p.In the glossary →× needed 90% of the blocks in a signalling period and has been in force since block 709,632 (14 November 2021).^[2]

Dive deeperHow does a soft fork activate?

Miners set a particular bit in the header of their blocks (version bits). Signals are counted in periods of 2,016 blocks, roughly two weeks. The standard procedure, BIP 9, requires 1,916 signalling blocks (95%); for Taproot, the threshold was lowered to 1,815 (90%).^[2] Once it is reached, the change is locked in and activates after a lead time.

Miners’ signalling is a coordination aid, not a binding vote. Which rules apply is decided by each node through the software it runs.

The block size war (2015–2017)

What was it about? Since 2010, blocks had been limited to 1 MB.^[3] As usage grew, blocks filled up and fees rose. Should the limit be raised via a hard fork?

For: more transactions per second and lower fees. Small blocks, supporters argued, would in the long run force high fees for fast confirmations.^[3]

Against: Larger blocks make running a full nodeGlossaryFull nodeA node that checks every block and every transaction itself against all the consensus rules. If you run a full node, you don’t have to trust anyone to know whether a payment is valid.In the glossary →× more expensive – fewer independent nodes mean more centralisation. Large blocks also propagate more slowly across the network.^[3]

How it ended: Hard-fork proposals such as Bitcoin XT (2015) and Bitcoin Classic (2016) failed to gain enough support.^[3] On 1 August 2017, big-block supporters split off with Bitcoin Cash – from block 478,559, initially with 8 MB blocks and with 32 MB blocks from 2018. In November 2018, Bitcoin Cash split again, into Bitcoin Cash and Bitcoin SV.^[4] Bitcoin itself activated the soft fork SegWitGlossarySegWit (Segregated Witness)A 2017 soft fork that treats signature data (the ‘witness’) separately. It fixed transaction malleability, increased block capacity and makes payments with modern addresses (bc1q…) cheaper.In the glossary →× on 24 August 2017 at block 481,824. It increased capacity without excluding old nodes.^[5],[3]

What does this mean for you? When buying, check for the ticker BTC – BCH and BSV are different currencies.^[4] And the question of what should happen on the blockchain itself and what on layers such as the Lightning Network still shapes Bitcoin today.

Ordinals and OP_RETURN: how much data belongs in the blockchain?

What is it about? Since January 2023, OrdinalsGlossaryOrdinals (inscriptions)A protocol that numbers individual satoshis and links them to content such as images or text (‘inscriptions’). Usable by anyone since January 2023; the data sits in Taproot scripts in the blockchain. Its usefulness is disputed.In the glossary →× inscriptions have been used to write images and text into the blockchain. They use Taproot scripts because, unlike other script types, these have no size limit of their own.^[6] A second route is OP_RETURNGlossaryOP_RETURNA command in Bitcoin’s scripting language that marks a transaction output as provably unspendable. It lets data be written into the blockchain. How much of it nodes should relay has been hotly disputed since 2025.In the glossary →× outputs. Bitcoin Core 30.0 (10 October 2025) relays such data up to 100,000 bytes by default instead of 83 bytes and allows several OP_RETURN outputs per transaction.^[7] Bitcoin Knots, by contrast, filters such transactions more strictly.^[8]

The dispute is about relay rules (policy): which unconfirmed transactions a node passes on to others. Under the consensus rules, these transactions were already valid.

The left column summarises a statement by 31 Core contributors dated 6 June 2025,^[9] the right column the rationale of BIP-110.^[10]

What does this mean for you? Little in everyday life: your payments work with both programs. If you run your own node, your choice of software determines which relay rules you support – more in Nodes & decentralisation.

BIP-110: from soft fork to split (2026)

What was it about? BIP-110 (‘Reduced Data Temporary Softfork’) aimed to limit data not via policy but via a consensus rule, for about a year – for example, OP_RETURN outputs back to 83 bytes and individual data pushes in transactions to 256 bytes. The soft fork was to activate once 55% of blocks signalled support. If that threshold hadn’t been reached by block 961,632, BIP-110 nodes were to accept only signalling blocks from there on for one signalling period (2,016 blocks).^[10]

For: the reasons in the right column above – but as a binding rule for everyone rather than a filter on your own node.^[10]

Against: A consensus change without broad agreement risks a split. The proposal itself concedes that funds in certain pre-signed Taproot transactions could theoretically be frozen or lost.^[10]

What happened: In the two weeks before the deadline, only 2.53% of blocks signalled support. From block 961,632 on 8 August 2026, BIP-110 nodes rejected non-signalling blocks and split off. Around eight hours later, their chain had found two blocks; the main chain was 48 blocks ahead by then.^[11] The proposal has since been marked ‘Closed’ in the BIP repository.^[10] Supporters then planned to continue their chain from 1 September 2026 via a hard fork with a different mining algorithm (BLAKE2b); no major exchangeTermExchange (crypto exchange)A trading platform where buyers and sellers trade bitcoin with each other via an order book.On the learning path: Stage 4 · Step 2 – Choosing a provider →In the glossary →AdLicensed providers with a paid linkProviders from our comparisonKrakenExchange · MiCA (Central Bank of Ireland)Visit Kraken* (paid link, opens in a new window)BitvavoExchange · MiCA (AFM, Netherlands)Visit Bitvavo* (paid link, opens in a new window)CoinbaseExchange · MiCA (CSSF, Luxembourg)Visit Coinbase* (paid link, opens in a new window)All 7 compared – including non-partners →*Paid link: if you sign up or buy through it, we earn a commission. Your price stays the same. How we make money →18+ · Crypto assets are highly volatile; you could lose all your money. No deposit protection.× had pledged support beforehand.^[12] For the latest status, see What’s changing right now.

What does this mean for you? Nothing has changed on the Bitcoin network.

If a split is coming

The warnings ahead of BIP-110 showed what matters in any split:^[13]

• Replay risk: Without replay protection, a transaction you send on one chain can also be valid on the other. If you sell fork coins, you might unintentionally spend your real bitcoin too.
• Exchange balances: If your bitcoin are on an exchange at the time of the split, the exchange decides whether and how to credit fork coins.
• Lightning: Open channels exist on both chains afterwards, but your node only watches one. It’s safer to close them beforehand.

What’s next?