Wiki / Concepts / Segregated Witness

Segregated Witness

From the Bitcoin Takeover Wiki · ✓ 6 sources · 0 podcast anchors · built 2026-11-13

The 2017 soft fork that moved signatures out of the legacy block, fixed malleability and became the centre of the block size war.

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The wiki's angle: SegWit is the reason most of the forks in this wiki exist. Bitcoin Cash split on 1 August 2017 rather than accept it.[4][3]

Contents

  1. What it changed
  2. Activation
  3. Forks over SegWit
  4. References

What it changed

BIP-141 specifies Segregated Witness at the consensus layer[1]. The SegWit2x announcement summarised what it required of upgrading software: changes to transaction serialisation, signature hashing, block weight, the scripting engine, a new address scheme and P2P messages, while noting that SegWit was opt-in for existing wallets[2].

Activation

Bitcoin Takeover's fork table records SegWit as a BIP-9 deployment on bit 1 that locked in from block 479,808 and became active at block 481,824 on 24 August 2017, “pushed over the line by BIP91 and BIP148”[3]. See UASF (BIP-148) and New York Agreement.

Forks over SegWit

Bitcoin Cash split from Bitcoin on 1 August 2017, before SegWit activated[4]. Bitcoin Gold, by contrast, kept SegWit[5]. The 2016 Hong Kong Roundtable had planned SegWit first and a hard fork afterwards[6].

References

  1. primaryBIP-141 (Segregated Witness, consensus layer) [archived]
  2. primarysegwit2x.github.io, “Bitcoin Upgrade at Block 494,784” [archived]
  3. btkBitcoin: All the Hard Forks and Soft Forks (BTCTKVR: Forks!) [archived]
  4. btkBitcoin Cash: The Big Block Breakaway (BTCTKVR: Forks!) [archived]
  5. btkBitcoin Gold: One GPU, One Vote (BTCTKVR: Forks!) [archived]
  6. primaryBitcoin Roundtable, “Bitcoin Roundtable Consensus”, Medium, 20 Feb 2016 (Wayback Machine copy)

Related

UASF (BIP-148)
The 2017 user-activated soft fork that threatened to reject non-SegWit-signalling blocks from 1 August 2017.
New York Agreement
The May 2017 industry deal to activate SegWit at 80% and hard fork to 2 MB within six months, which became Seg
Bitcoin Cash
The big-block fork of 1 August 2017, Bitcoin's first durable chain split.
Hard fork vs soft fork
The two ways to change Bitcoin's rules: soft forks tighten them and stay backward-compatible; hard forks loose
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