Mattermost team here. Agree we could have done a better job communicating. The change started in 2023 and we had made a lot of effort to work with the largest unsupported deployments early.

They were very aware of the direction ahead of the August 2025 announce. From then, there was still over a year of support during the transition: https://forum.mattermost.com/t/mattermost-v11-changes-in-fre...

Our understanding is that the organizations most impacted were those using the unsupported Mattermost commercial version, not the open source version. The commercial version of Mattermost is offered in Docker, K8, etc.

If you look into the license of the Mattermost instance you ran, what is the "Enterprise Edition" (i.e. commercial version that upgrades into paid offering) or under MIT license (open source licensed offering, bundled with GitLab omnibus)?