SegWit (2017) moved signatures into a separate witness section, fixing malleability, discounting signature data and making Lightning practical.
What changed
SegWit activated at block 481,824 in August 2017. It segregates (separates) the witness, meaning signatures and public keys, from the rest of the transaction.
Three big effects
- Malleability fixed. The txid no longer includes signatures, so nobody can change a txid by tweaking a signature. That made the The Lightning Network practical.
- More capacity. Blocks are measured by weight and witness data is discounted, so more transactions fit.
- Script upgrades. SegWit outputs carry a version number, so new script types can be added cleanly. Taproot is version 1.
SegWit output types
| Type | Address | Holds |
|---|---|---|
| P2WPKH | bc1q… (42 chars) | 20-byte public key hash |
| P2WSH | bc1q… (62 chars) | 32-byte script hash |
| P2SH-P2WPKH | 3… | SegWit wrapped in Pay to script hash (P2SH) for old wallets |
A soft fork
Old nodes see SegWit outputs as "anyone can spend", but upgraded nodes enforce the real rules, and miners follow them. Old nodes stay compatible. See Soft forks and hard forks.
See the activation block
Block 481,824 on MyBitcoinExplorer is where SegWit rules began being enforced in August 2017. Transactions after it can carry witness data; blocks can hold more than 1 MB.
Is SegWit still used?
Yes, heavily. Native SegWit (bc1q) remains one of the most common output types, alongside Taproot (bc1p).
Key takeaways
- SegWit separated signatures into a witness section in 2017.
- It fixed txid malleability and discounted witness data.
- It introduced versioned outputs; Taproot is version 1.
Common questions
Do I need SegWit?
Using a bc1q or bc1p wallet means lower fees. Every major wallet supports it.
Is SegWit the same as SegWit2x?
No. SegWit2x was a separate, abandoned proposal to also double the block size by hard fork.
Does SegWit lower fees?
Yes. Witness data is discounted, so SegWit inputs cost less to spend.
Is SegWit compatible with old wallets?
Old wallets can still send to nested SegWit (3…) addresses; modern wallets support bc1 addresses directly.