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TERM_DEF // UPGRADES_BIPS / BIP_361_POST_QUANTUM_MIGRATION_LEGACY_SIGNATURE_SUNSET
BIP 361 (POST-QUANTUM MIGRATION
& LEGACY SIGNATURE SUNSET)
BIP 361 (Post-Quantum Migration & Legacy Signature Sunset). Draft migration roadmap deprecating ECDSA/Schnorr in favour of PQ signatures.

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_361_POST_QUANTUM_MIGRATION_LEGACY_SIGNATURE_SUNSET_IS
BIP 361 (Post-Quantum Migration & Legacy Signature Sunset) — at a glance
UPGRADES
BIP 361 — "Post-Quantum Migration & Legacy Signature Sunset" is a proposal in the Post-Quantum family, first published in 2025 with status draft (fork/">soft fork). Draft migration roadmap deprecating ECDSA/Schnorr in favour of PQ signatures. Its technical mechanism: consensus rule eventually rejecting spends of pre-PQ outputs after a deadline. companion to BIP-360 for the great post-quantum migration
Why it exists
DESIGN
BIP 361 (Post-Quantum Migration & Legacy Signature Sunset) exists to solve a specific problem: sunset legacy ECDSA-only outputs that are vulnerable to quantum attack. 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-361 is the single source of truth for this concern, so any new client built today can match the behaviour of every client built since 2025.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
Mechanically, BIP-361 consensus rule eventually rejecting spends of pre-PQ outputs after a deadline. 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: companion to BIP-360 for the great post-quantum migration.
1. Author drafts BIP-361 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-361) 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-361 is promoted to "final"; deprecated proposals get "replaced" or "withdrawn".
WORKED_EXAMPLE
BIP-361 — quick reference card
EXAMPLE
BIP number : 361 Title : Post-Quantum Migration & Legacy Signature Sunset Area : Post-Quantum First published: 2025 Status : draft Fork class : soft Motivation : sunset legacy ECDSA-only outputs that are vulnerable to quantum attack. Mechanism : consensus rule eventually rejecting spends of pre-PQ outputs after a deadline. Where it shows up : companion to BIP-360 for the great post-quantum migration. Read the spec : https://github.com/bitcoin/bips/blob/master/bip-0361.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-361 means the same thing across every wallet, miner, and node that has read this spec.
CONSENSUS
BIP-361 is a soft fork — it changes (or proposes to change) the rules every full node enforces.
DRAFT
BIP-361 is still in draft — reference code may exist but mainnet adoption is partial or pending.
COMMON_PITFALLS
Things that catch people out
PITFALLS
  • BIP-361 is still in DRAFT status — its details can change before activation, and any code built against it may need adjustment.
  • BIP-361 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:
Segregated Witness (SegWit, BIP 141) Taproot (BIP 341) Tapscript (BIP 342) Schnorr (BIP 340) BIP Process Soft Fork Activation MASF (Miner-Activated Soft Fork) UASF (User-Activated Soft Fork)
TERMINOLOGY_INDEX
TERMINOLOGY
BIP 361 (Post-Quantum Migration & Legacy Signature Sunset)
Draft migration roadmap deprecating ECDSA/Schnorr in favour of PQ signatures.
Segregated Witness (SegWit, BIP 141)
The 2017 upgrade separating witness-data/">witness data, fixing tx malleability, and introducing weight units.
Taproot (BIP 341)
The 2021 upgrade introducing key-aggregable Schnorr signatures and Merkleized script trees.
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
The mechanism (versionbits, MASF, UASF, Speedy Trial) by which soft forks turn on.
MASF (Miner-Activated Soft Fork)
Activation triggered by miner signaling in block versions.