---
xip: 72
title: Client enforcement of protocol version on specific commits and groups
description: Tool for protocol developers to protect users on old versions from getting groups in a bad state when releasing breaking changes
author: Cameron Voell (@cameronvoell)
status: Final
type: Standards
category: XRC
created: 2025-03-05
---
## Abstract
In XMTP Protocol, breaking changes can sometimes cause errors in existing groups that are difficult or impossible to recover from without just starting over from scratch with a new group. Two ways around this are blocking users on old versions from using the network (API Enforcement, or “The Hammer”), and Group Enforcement using MLS [required capabilities](https://www.rfc-editor.org/rfc/rfc9420.html#section-11.1) extension and [Group Reinitialization](https://www.rfc-editor.org/rfc/rfc9420.html#name-reinitialization). This proposal is for a third type of enforcement, Client Enforcement, where older clients will pause individual groups when they receive a commit message that specifies a min LibXMTP version that is higher than their current version.
## Specification
For the purposes of this proposal, the LibXMTP GitHub repo MLS crate cargo package version will serve as the source of truth of each client version.
### How to communicate `minimum_supported_protocol_version`
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