# Soft forks and hard forks

A soft fork tightens Bitcoin's rules so old nodes keep working; a hard fork loosens them so old nodes reject the new chain. Learn the difference.

Canonical page: https://mybitcoinexplorer.com/learn/soft-forks-and-hard-forks
Topic: Nodes and the network
Published: 2026-10-29
Updated: 2026-10-30


## Soft fork: stricter rules
New rules only **forbid** things that used to be allowed. Blocks valid under the new rules are still valid to old nodes, so the network stays together even if some nodes don't upgrade.

> Diagram: Soft fork: the new rules are a subset of the old rules — soft

Examples: [Pay to script hash (P2SH)](https://mybitcoinexplorer.com/learn/p2sh) (2012), CLTV (2015), CSV (2016), [Segregated Witness (SegWit)](https://mybitcoinexplorer.com/learn/segwit) (2017), [Taproot](https://mybitcoinexplorer.com/learn/taproot) (2021).

## Hard fork: looser rules
New rules **allow** something old nodes reject, like bigger blocks. Old nodes see those blocks as invalid and stay on the old chain. If both sides keep going, you get two coins.

> Diagram: Hard fork: new rules allow blocks old nodes reject — hard

Bitcoin hasn't had a planned hard fork in its main history. In 2017, Bitcoin Cash split off through a hard fork to allow bigger blocks.

## How soft forks activate
| Method | How it works |
|---|---|
| Miner signalling (BIP 9) | Activates when enough blocks in a period signal readiness |
| Speedy Trial | Short signalling window with a delayed activation (used for Taproot) |
| User-activated (UASF) | Nodes enforce from a date regardless of miner signals (BIP 148 in 2017) |

Signalling isn't voting: it coordinates timing so miners are ready to follow the new rules.


## Bitcoin's soft forks
| Year | Upgrade | What it added |
|---|---|---|
| 2012 | P2SH (BIP 16) | Pay to script hash |
| 2015 | CLTV (BIP 65) | Absolute timelocks |
| 2016 | CSV (BIPs 68, 112, 113) | Relative timelocks |
| 2017 | SegWit (BIP 141) | Witness data, weight limit |
| 2021 | Taproot (BIPs 340–342) | Schnorr, Taproot, Tapscript |


## Key takeaways

- Soft forks tighten rules and stay compatible with old nodes.
- Hard forks loosen rules and can split the chain.
- SegWit and Taproot were soft forks.

## Common questions

### Is a hard fork always bad?

Not inherently, but it needs everyone to upgrade, so in Bitcoin it's seen as risky and is avoided.

### Do I need to upgrade for a soft fork?

Your old node keeps working, but to enforce the new rules yourself, you upgrade.

### Is a chain split always a hard fork?

Splits come from rule differences. A hard fork that not everyone adopts creates a split; a soft fork usually doesn't.

### What was Bitcoin Cash?

A 2017 hard fork that split from Bitcoin to allow larger blocks; it is a separate coin.

## Related lessons

- [Consensus rules](https://mybitcoinexplorer.com/learn/consensus-rules)
- [Bitcoin Improvement Proposals (BIPs)](https://mybitcoinexplorer.com/learn/bitcoin-improvement-proposals-bips)
- [Segregated Witness (SegWit)](https://mybitcoinexplorer.com/learn/segwit)
- [Taproot](https://mybitcoinexplorer.com/learn/taproot)