Why is OpenSearch 1.x support being dropped?
OpenSearch 1.x reached end-of-life in May 2025. Continuing to support it requires maintaining compatibility shims for an API surface that has meaningfully diverged from OpenSearch 2.x, and it prevents Mattermost from adopting improvements available in the modern OpenSearch client.
Rather than carry that burden indefinitely, we are setting a minimum supported version of OpenSearch 2.x, which has been stable and widely adopted since its release in 2022.
What will I see if I try to run Mattermost v12.0+ with OpenSearch 1.x?
The server will refuse to activate the OpenSearch search backend and will log an error similar to:
OpenSearch version 1 is lower than min supported version of 2
Is Mattermost dropping OpenSearch support entirely?
Absolutely not. Mattermost continues to fully support OpenSearch 2.x and 3.x. Only the 1.x line is affected.
What are my options?
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Upgrade to OpenSearch 2.x or 3.x. OpenSearch provides an in-place upgrade path from 1.x to 2.x. This is the most direct route for existing OpenSearch deployments.
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Use a managed OpenSearch service. If you are using Amazon OpenSearch Service or another managed offering, upgrade your domain to OpenSearch 2.x or later through your provider’s console.
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Switch to Elasticsearch. Mattermost also supports Elasticsearch 8.x and 9.x as a search backend.
When does this take effect?
Mattermost v12.0 (October 2026) is the first release that requires OpenSearch 2.x or newer. If you need more time to plan your migration, you can remain on v11 releases while you prepare. We recommend completing your migration before the v11.7 ESR reaches the end of its support window.