BIP Draft: Flag day activation based on nLockTime signaling

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BIP: XXX  
Layer: Consensus (soft fork)  
Title: nLockTime signaling and flag day activation
Author: /dev/fd0 <alicexbt@protonmail.com>  
Status: Draft  
Type: Standards Track  
Created: 2024-08-19  
License: Public Domain

Abstract

This document describes a process to activate soft forks using flag day after nLockTime signaling and discussion.

Motivation

BIP 8 and BIP 9 are controversial. This BIP is an alternative which addresses the problems with other activation methods.

Specification

• Assign numbers to different soft fork proposals or use their BIP numbers
• Users can broadcast their transactions with one of these numbers used as nLockTime to show support
• Miners inlcuding a transaction in block would signal readiness for a soft fork
• Community can analyze these transactions after 3 months and prepare for a flag day activation of soft fork

Example:

Use 119 to signal support for OP_CHECKTEMPLATEVERIFY in nLockTime

Reference implementation

Activation: https://github.com/bitcoin/bitcoin/commit/ab91bf39b7c11e9c86bb2043c24f0f377f1cf514.diff

Exclusion in relay or mining: https://github.com/bitcoinknots/bitcoin/commit/18cd7b0ef6eaeacd06678c6d192b6cacc9d7eee5.diff

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If a transaction does not get included in block for a long time, users can replace it with another transaction spending same inputs and use a different nLockTime.