TERM_DEF // UPGRADES_BIPS / BIP_144_SEGWIT_TRANSACTION_SERIALIZATION
BIP 144 (SEGWIT
TRANSACTION SERIALIZATION)
TRANSACTION SERIALIZATION)
BIP 144 (transaction/">SegWit Transaction Serialization). Spec for the marker/flag/witness-bearing transaction serialization.
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_BIP_144_SEGWIT_TRANSACTION_SERIALIZATION_IS
BIP 144 (SegWit Transaction Serialization) — at a glance
UPGRADES
BIP 144 — "SegWit Transaction Serialization" is a proposal in the SegWit family, first published in 2016 with status final (fork/">soft fork). Spec for the marker/flag/witness-bearing transaction serialization. Its technical mechanism: marker + flag bytes in tx serialisation; legacy nodes see a stripped-down tx. enables every SegWit tx to be relayed peer-to-peer-p2p/">peer-to-peer
Why it exists
DESIGN
BIP 144 (SegWit Transaction Serialization) exists to solve a specific problem: serialise witness data over the P2P network without breaking old nodes. 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-144 is the single source of truth for this concern, so any new client built today can match the behaviour of every client built since 2016.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
Mechanically, BIP-144 marker + flag bytes in tx serialisation; legacy nodes see a stripped-down tx. 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: enables every SegWit tx to be relayed peer-to-peer.
1. Author drafts BIP-144 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-144) 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-144 is promoted to "final"; deprecated proposals get "replaced" or "withdrawn".
WORKED_EXAMPLE
BIP-144 — quick reference card
EXAMPLE
BIP number : 144
Title : SegWit Transaction Serialization
Area : SegWit
First published: 2016
Status : final
Fork class : soft
Motivation : serialise witness data over the P2P network without breaking old nodes.
Mechanism : marker + flag bytes in tx serialisation; legacy nodes see a stripped-down tx.
Where it shows up : enables every SegWit tx to be relayed peer-to-peer.
Read the spec : https://github.com/bitcoin/bips/blob/master/bip-0144.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-144 means the same thing across every wallet, miner, and node that has read this spec.
BIP-144 is a soft fork — it changes (or proposes to change) the rules every full node enforces.
DEPLOYED
Implementations of BIP-144 are in production. The behaviour is observable on mainnet today.
COMMON_PITFALLS
Things that catch people out
PITFALLS
- BIP-144 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
BIP 144 (SegWit Transaction Serialization)
Spec for the marker/flag/witness-bearing transaction serialization.
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.