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Version bits with timeout and delay

BIP 9. Pieter Wuille.

BIP 9, Version bits with timeout and delay. This document specifies a proposed change to the semantics of the 'version' field in Bitcoin blocks, allowing multiple backward-compatible changes (further called "soft forks") to be deployed in parallel.

Status in the source: Deployed. A reading of the public specification, not a copy of it and not a certification.

Version bits with timeout and delay is worth reading for the rule it actually adds: This document specifies a proposed change to the semantics of the 'version' field in Bitcoin blocks, allowing multiple backward-compatible changes (further called "soft forks") to be deployed in parallel.
Evidence
Primary paper
Re-measured
No
Assumptions
3
Records linked
3

Code

Source, repository, and what is actually hosted

  • BIP 9https://bips.dev/9
  • The source URL is not a GitHub repository. No code remote is invented.
  • Full text is not mirrored. Public availability is not a licence to copy the file onto this site.
  • Add to a reading list

01 Claim ledger

What the paper is allowed to say

Each row is a sentence already in the study. The status is the same on every row: a model claim, not a live measurement.

  1. Claim 01 · Paper model

    The rule

    This document specifies a proposed change to the semantics of the 'version' field in Bitcoin blocks, allowing multiple backward-compatible changes (further called "soft forks") to be deployed in parallel.

  2. Claim 02 · Paper model

    What was already failing

    A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

  3. Claim 03 · Paper model

    What the number does not mean

    The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

  4. Claim 04 · Paper model

    What a builder should be able to point at

    An implementation either constrains Version bits with timeout and delay or it is a different design.

02 Three cuts

Observation, model, falsifier

A desk does not stop at the summary. Each claim is cut three ways, using only this study's own assumptions and checks. Nothing here is a new figure.

  1. 01 The rule

    Observation

    What the study says

    This document specifies a proposed change to the semantics of the 'version' field in Bitcoin blocks, allowing multiple backward-compatible changes (further called "soft forks") to be deployed in parallel.

    Model

    What has to hold

    The object that has to change is Version bits with timeout and delay. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    What is covered by the signed bytes in Version bits with timeout and delay?

  2. 02 What was already failing

    Observation

    What the study says

    A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

    Model

    What has to hold

    The object that has to change is Version bits with timeout and delay. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    Can the same signature be replayed on another chain, account, or message?

  3. 03 What the number does not mean

    Observation

    What the study says

    The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

    Model

    What has to hold

    You are implementing BIP 9 at the status the text itself states: Deployed.

    Falsifier

    What would retire it

    Which primitive does the text require: Version bits with timeout and delay?

  4. 04 What a builder should be able to point at

    Observation

    What the study says

    An implementation either constrains Version bits with timeout and delay or it is a different design.

    Model

    What has to hold

    The object that has to change is Version bits with timeout and delay. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    What is covered by the signed bytes in Version bits with timeout and delay?

03 Sequence

One action, as an operating tape

  1. 01Open BIP 9 and read the status line before the examples.
  2. 02Write down the rule in one sentence. A fair version of that sentence is: This document specifies a proposed change to the semantics of the 'version' field in Bitcoin blocks, allowing multiple backward-compatible changes (further called "soft forks") to be deployed in parallel.
  3. 03Name the object that changes: Version bits with timeout and delay.
  4. 04Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

04 Load-bearing

The argument, and where a pitch drops it

  1. What the text is allowed to settle

    The cut

    Bitcoin Improvement Proposal 9 can settle the shape of Version bits with timeout and delay. It cannot settle whether a later client, a later fork, or a later wallet still does this.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    Wallet support is not the same as consensus validity.

  2. What this page will not pretend

    The cut

    There is no benchmark, no adoption number, and no claim that the mechanism is safe outside the assumptions written in the source.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

05 Register

What has to be true

  • Model · Not re-measured

    You are implementing BIP 9 at the status the text itself states: Deployed.

  • Network · Not re-measured

    The object that has to change is Version bits with timeout and delay. A neighbouring document with a similar name is not this one.

  • Model · Not re-measured

    Wallet support is not the same as consensus validity.

06 Divergence

What happened after the paper

The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it. Later documents can narrow, replace, or ignore this one. Cite the number you mean.

A later client, parameter set, or reward formula is a different object. Cite this paper for the mechanism. Cite a primary release for the network. This desk has not re-run the proof.

07 Pre-mortem

What to check before you use the idea

  4. 0 of 3 marked on this browser. A mark is a reading note, not a pass, a rating, or a recommendation.

08 Anatomy

The paper, in the order a builder needs

The problem it names

A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

What the design proposes

  • This document specifies a proposed change to the semantics of the 'version' field in Bitcoin blocks, allowing multiple backward-compatible changes (further called "soft forks") to be deployed in parallel.
  • It relies on interpreting the version field as a bit vector, where each bit can be used to track an independent change.
  • Once the consensus change succeeds or times out, there is a "fallow" pause after which the bit can be reused for later changes.

How the mechanism is specified

  • Taken from the specification, the next constraint is: It relies on interpreting the version field as a bit vector, where each bit can be used to track an independent change.
  • Locate Version bits with timeout and delay in BIP 9 and apply it to one transaction or call.
  • Then check the failure the class of rule always has: a node that did not upgrade, a reverted call, a replayed signature, or a peer that does not speak the message.

What this page does not treat as proven

  • A signature scheme is not a privacy system. It hides the signer only if the protocol says so.
  • Wallet support is not the same as consensus validity.
  • The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

Why the desk still reads it

Use BIP 9 when a pitch says 'Version bits with timeout and delay' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.

09 Lexicon

Terms, opened into the record

BIP 9
The public text titled Version bits with timeout and delay.
Deployed
The document's own label for how finished the text is. It is not a market fact.

10 Repository

Every linked record on this page

Underlined words open a page that already exists: a concept, a protocol profile, a failure record, or another paper. If a word is not underlined, this desk does not have a record for it.

Protocols

This is Blockchain Lab's reading of a public design paper. It is not the paper, not a copy of it, and not an offer of tokens, equity, custody or a partnership. Later network behaviour can diverge from the text. Nothing here is investment, legal or technical advice.

Research status: Design paper. Last reviewed: 1 October 2026. This is a reading of a public paper, not investment, legal or security advice.