TERM_DEF // UPGRADES_BIPS / SEGREGATED_WITNESS_SEGWIT_BIP_141
SEGREGATED WITNESS (SEGWIT,
BIP 141)
BIP 141)
witness-segwit-bip-141/">Segregated Witness (SegWit, BIP 141). The 2017 upgrade separating witness data, fixing tx malleability, and introducing weight units.
This page sits in the Upgrades & BIPs section — The proposal process and the major upgrades that shaped Bitcoin. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
This page sits in the Upgrades & BIPs section — The proposal process and the major upgrades that shaped Bitcoin. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
WHAT_SEGREGATED_WITNESS_SEGWIT_BIP_141_IS
Segregated Witness (SegWit, BIP 141) — at a glance
UPGRADES
BIP 141 is a proposal in the SegWit family, first published in 2015 with status final (fork/">soft fork). The 2017 upgrade separating witness data, fixing tx malleability, and introducing weight units. Its technical mechanism: witness data separated from txid hash; weight metric (4× discount on witness bytes). activated August 2017; enabled Lightning Network on the base layer
Why it exists
DESIGN
Segregated Witness (SegWit, BIP 141) exists to solve a specific problem: fix transaction-malleability/">transaction malleability and increase effective block capacity. Without a written, numbered spec, every wallet and node implementer would interpret the requirement differently — and Bitcoin's value depends on every implementation agreeing exactly. BIP-141 is the single source of truth for this concern, so any new client built today can match the behaviour of every client built since 2015.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
Mechanically, BIP-141 witness data separated from txid hash; weight metric (4× discount on witness bytes). Because this is a soft fork, old software accepts new behaviour without modification — but new behaviour is rejected if old software produces it. Adoption today: activated August 2017; enabled Lightning Network on the base layer.
1. Author drafts BIP-141 against the BIP-2 template — abstract, motivation, specification, rationale.
2. The text + a reference implementation are posted on the bitcoin-dev list and as a PR to bitcoin/bips.
3. Reviewers tear it apart: ambiguities, security concerns, edge cases, interaction with prior BIPs.
4. Once stable, the BIP editor merges it; it gets a number (BIP-141) and the status "draft" or "proposed".
5. Implementations land in Bitcoin Core / wallets / other clients. For consensus changes: activation parameters chosen.
6. After deployment + adoption, BIP-141 is promoted to "final"; deprecated proposals get "replaced" or "withdrawn".
WORKED_EXAMPLE
BIP-141 — quick reference card
EXAMPLE
BIP number : 141
Title : Segregated Witness (SegWit, BIP 141)
Area : SegWit
First published: 2015
Status : final
Fork class : soft
Motivation : fix transaction malleability and increase effective block capacity.
Mechanism : witness data separated from txid hash; weight metric (4× discount on witness bytes).
Where it shows up : activated August 2017; enabled Lightning Network on the base layer.
Read the spec : https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki
KEY_PROPERTIES
OPT-IN
No authority can force a BIP on anyone. Adoption depends entirely on whether the change is genuinely useful.
NUMBERED
Stable numeric reference — BIP-141 means the same thing across every wallet, miner, and node that has read this spec.
BIP-141 is a soft fork — it changes (or proposes to change) the rules every full node enforces.
DEPLOYED
Implementations of BIP-141 are in production. The behaviour is observable on mainnet today.
COMMON_PITFALLS
Things that catch people out
PITFALLS
- BIP-141 is a soft fork — old clients accept new behaviour but don't enforce it. Validate against an upgraded node to be sure the rule is being checked.
- Don't confuse "draft" / "proposed" / "final" status — read the BIP header before relying on it in production.
- The BIP number is just an editorial counter — it doesn't imply correctness or stability. Always cross-reference with the latest bitcoin/bips repo.
RELATED_CONCEPTS
Other terms from Upgrades & BIPs — click any to read its page:
TERMINOLOGY_INDEX
TERMINOLOGY
Segregated Witness (SegWit, BIP 141)
The 2017 upgrade separating witness data, fixing tx malleability, and introducing weight units.
Taproot (BIP 341)
Tapscript (BIP 342)
Script-language updates accompanying Taproot — new opcodes, removed limits.
Schnorr (BIP 340)
The Schnorr signature spec adopted by Taproot.
BIP Process
The community workflow for proposing, discussing, and tracking changes to Bitcoin.
Soft Fork Activation
MASF (Miner-Activated Soft Fork)
Activation triggered by miner signaling in block versions.
UASF (User-Activated Soft Fork)
Activation enforced by economic nodes regardless of miner signaling.