BA-09 · LESSON 07

Consensus changes and BIPs

KEY DEFINITIONS

Terms used in this lesson

BIP: Bitcoin Improvement Proposal: a numbered technical document describing a Bitcoin standard, process, or proposed change.

Soft forks tighten validity rules and require deployment coordination across users, miners, software, and markets.

55 min Difficulty 3/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · soft fork deploymentA soft fork moves from specification to local enforcementSelect any state to inspect its exact role.

RELATIONSHIP MAPOrdered mechanism flow

01
SPECIFYNew rule, test vectors, and edge cases
A numbered or merged BIP is documentation. It does not change consensus by itself.
02
IMPLEMENTUpgraded release validates new rule
Users choose software. Different versions can temporarily enforce different validity sets.
03
SIGNALDefined threshold reached
Version-bit or other signaling follows a proposal-specific state machine and indicates readiness rather than sovereign voting power.
04
ACTIVATERule becomes active
Lock-in, activation height, timeout, and minimum activation conditions are distinct states defined by the deployment.
05
ENFORCEUpgraded nodes reject violations
After activation, an upgraded node rejects a new-rule violation even when an older node would still accept it.

Rule shown: A BIP documents the proposal, deployment coordinates activation, and each upgraded full node independently enforces the tighter validity set after activation.

STAGE 1 OF 5SPECIFY: New rule, test vectors, and edge cases

A numbered or merged BIP is documentation. It does not change consensus by itself.

Governing relationship: A BIP documents the proposal, deployment coordinates activation, and each upgraded full node independently enforces the tighter validity set after activation. Complete path: 1. SPECIFY, New rule, test vectors, and edge cases. A numbered or merged BIP is documentation. It does not change consensus by itself. 2. IMPLEMENT, Upgraded release validates new rule. Users choose software. Different versions can temporarily enforce different validity sets. 3. SIGNAL, Defined threshold reached. Version-bit or other signaling follows a proposal-specific state machine and indicates readiness rather than sovereign voting power. 4. ACTIVATE, Rule becomes active. Lock-in, activation height, timeout, and minimum activation conditions are distinct states defined by the deployment. 5. ENFORCE, Upgraded nodes reject violations. After activation, an upgraded node rejects a new-rule violation even when an older node would still accept it.

1. State transitionWhat exists, what changes, and what results

BEFORE

A proposal defines a 100-block window and 90-block readiness threshold. Exactly 92 valid blocks signal in one window.

MECHANISM

A consensus BIP defines new validity conditions, test vectors, compatibility, rationale, and edge cases. Ambiguous intent is not executable consensus.

AFTER

Deployment state and enforcement are separate transitions; the BIP's exact state machine determines both.

Text equivalent: Starting from A proposal defines a 100-block window and 90-block readiness threshold. Exactly 92 valid blocks signal in one window. The mechanism begins when A consensus BIP defines new validity conditions, test vectors, compatibility, rationale, and edge cases. Ambiguous intent is not executable consensus. The resulting lesson is Deployment state and enforcement are separate transitions; the BIP's exact state machine determines both.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Specify the rule exactly

A consensus BIP defines new validity conditions, test vectors, compatibility, rationale, and edge cases. Ambiguous intent is not executable consensus.

Complete path: 1. Specify the rule exactly: A consensus BIP defines new validity conditions, test vectors, compatibility, rationale, and edge cases. Ambiguous intent is not executable consensus. 2. Implement and review: Multiple reviewers trace parsing, activation, reorg, resource, wallet, and adversarial effects before broad deployment. 3. Distribute compatible software: Node operators, miners, wallets, and services choose versions and prepare for the proposed activation conditions. 4. Measure or trigger readiness: Some deployments use version-bit signaling over defined windows and thresholds; others use height or separate coordination. Signaling semantics are proposal-specific. 5. Enforce after activation: Upgraded nodes reject blocks violating the tightened rule. Older nodes may accept those blocks under old rules, creating risk if enforcement lacks sufficient coordination.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

The pinned period state machine moves through defined, started, locked in, active, or failed using completed-window signaling, timeout, and minimum activation rules.

CHANGED CONDITION

After activation an upgraded node rejects a new-rule violation even when an older node accepts it, exposing the coordination split the deployment sought to avoid.

Important distinction: A BIP becomes a Bitcoin rule when it is assigned a number or merged into a repository. A BIP is documentation. Consensus behavior changes only when software implementing it is adopted and its specified activation conditions are met.

Text equivalent: The accepted path is enforced by The pinned period state machine moves through defined, started, locked in, active, or failed using completed-window signaling, timeout, and minimum activation rules. If the required condition changes, After activation an upgraded node rejects a new-rule violation even when an older node accepts it, exposing the coordination split the deployment sought to avoid.

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Learn the idea

A Bitcoin Improvement Proposal, or BIP, documents a standard, process, or consensus proposal. A soft fork tightens consensus validity. Deployment is how participants coordinate enforcement, often using software releases, signaling mechanisms, activation heights, or other defined rules. Miner signaling can indicate readiness but does not grant miners authority to override node validation.

GUIDED EXPLANATION1/5 ideas inspected

Specify the rule exactly

A consensus BIP defines new validity conditions, test vectors, compatibility, rationale, and edge cases. Ambiguous intent is not executable consensus.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“A BIP becomes a Bitcoin rule when it is assigned a number or merged into a repository.”

A BIP is documentation. Consensus behavior changes only when software implementing it is adopted and its specified activation conditions are met.

FINISH LEARNING FIRST

The questions unlock after every required learning activity

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