01Definition
SegWit moves transaction witness data into a separate serialization structure. It fixes third-party transaction malleability for SegWit spends and increases effective block capacity through a weight-based limit.
02Why malleability mattered
Before SegWit, a transaction identifier could be changed without invalidating the payment. Stable transaction IDs made pre-signed chains of unconfirmed transactions safer, an important foundation for Lightning channels.
03Compatibility
SegWit was deployed as a soft fork. Older nodes could continue to follow the chain without understanding the new witness rules, while upgraded nodes enforced them.
⌖Reference points
01
Activated 24 August 2017
02
Fixes third-party transaction malleability
03
Introduces block weight
04
Enabled safer Lightning construction