Definition
Lazy consensus is the informal decision-making model used by the Bitcoin Core project. There is no formal voting, no board, and no committee that ratifies code changes. Instead, a proposed change accumulates public peer review, and a merge maintainer assesses whether it has rough consensus among contributors before merging. The word "lazy" reflects that silence is not assent: a change advances because reviewers actively support it and no one raises an unrebutted objection, not because nobody happened to comment.
How review is expressed
Reviewers signal positions in a shared vocabulary. A Concept ACK agrees with the goal; an Approach ACK agrees with the method; a plain ACK or tested ACK (tACK) means the reviewer examined and exercised the code and supports merging. A NACK is an objection and, to carry weight, must include a sound technical rationale. NACKs without reasoning may be disregarded.
Why it matters
This model deliberately makes changes to consensus-critical software slow and hard to push through. It resists capture, because no single actor can unilaterally approve a change, and it favors objections that are technically grounded over those backed by social pressure or stake.
Maintainers weigh review according to demonstrated expertise; see the Bitcoin Core maintainer role and the broader code review culture.
In Simple Terms
Lazy consensus is the informal decision-making model used by the Bitcoin Core project. There is no formal voting, no board, and no committee that ratifies…