Topic · How blockchains work
What is SegWit?
- Quick fact 1
SegWit is defined in BIP 141 and was deployed as a soft fork.
- Quick fact 2
SegWit separates (segregates) signature “witness” data from the rest of the transaction.
- Quick fact 3
Taproot later added SegWit version 1 spending rules.
The short lesson
SegWit, short for Segregated Witness, was a bitcoin upgrade activated in 2017 as a soft fork.
The “witness” is the signature data that proves you can spend. SegWit moved it into a separate part of the transaction. That did three useful things:
- Fixed malleability. Before SegWit, a transaction’s ID could be changed by tweaking its signature. Fixing that made second-layer systems like the Lightning Network practical.
- More room per block. Witness data is counted at a discount, so blocks can fit more transactions.
- Lower fees for SegWit users, because their transactions take less counted space.
How you see it
Native SegWit addresses start with bc1q. Older ones start with 1 or 3. All of them work for receiving bitcoin, but check that the sending service supports the format.
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Related terms
Go deeper in Lesson 6: What a network fee is
More in How blockchains work
Common questions
Should I use a bc1 address?
Most modern wallets default to one. They often mean lower fees.
Can old wallets send to bc1 addresses?
Most can today. A few very old services may not.
Was SegWit a hard fork?
No. It was a soft fork, so old nodes kept working.
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Reviewed and sources
Written and reviewed by Joshua Baskin, founder. Last reviewed . How we check facts · Report an error
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