> For the complete documentation index, see [llms.txt](https://docs.leather.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.leather.io/learn/segwit.md).

# What is Segregated Witness (SegWit)?

SegWit (Segregated Witness) is the 2017 Bitcoin upgrade that separated signature data, lowered fees and fixed transaction malleability.

SegWit (Segregated Witness) is a Bitcoin upgrade that activated in August 2017 as a soft fork. It moved the signature data, the witness, into a separate part of each transaction.

## What SegWit changed

* **Block capacity:** blocks are measured in weight, at most 4 million units. Witness data counts for a quarter of the weight of other data, so more transactions fit in a block.
* **Fees:** SegWit transactions weigh less, so they cost less to send.
* **Malleability:** the TXID no longer covers the witness, so nobody can change a transaction's ID before it confirms. See [What is Transaction Malleability?](/learn/transaction-malleability.md).
* **Layers:** reliable TXIDs made the Lightning Network practical.

The upgrade was debated for years before it activated, and part of that disagreement led to a split that created Bitcoin Cash.

## SegWit address types

* **Nested SegWit (P2SH)** addresses start with `3` and work with wallets that predate SegWit. See [What is a Bitcoin SegWit Address?](/learn/what-is-a-bitcoin-segwit-address.md).
* **Native SegWit (P2WPKH, bech32)** addresses start with `bc1q` and give the lowest fees of the two. See [What is a Native SegWit Address?](/learn/what-is-a-native-segwit-address.md).

Taproot addresses (`bc1p`), from the 2021 Taproot upgrade, also use witness data. See [What Are Taproot addresses?](/learn/taproot-address.md).

## SegWit in Leather

Leather creates a Native SegWit and a Taproot address for each account, so your Bitcoin transactions get SegWit fee savings. It sends to every address type.