Add docs on version compatibility within a deployment

docs/content/about/releases.mdx

@@ -44,6 +44,16 @@ While technically the 0.y.z phase of Semantic Versioning is "anything goes", we
 
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+## Version compatibility wihin a Dagster deployment
+
+Dagster deployments can have multiple versions of Dagster running simultaneously.
+
+A Dagster deployment consists of a set of [code locations](https://docs.dagster.io/concepts/code-locations), as well as _host processes_: the web server and [daemon](https://docs.dagster.io/deployment/dagster-daemon).
+- The code locations within a deployment can each depend on a different Dagster version.
+- The host processes within a deployment are expected to all have the same Dagster version, and that Dagster version is expected to be greater than or equal to the greatest Dagster version used by any code location within the deployment. In Dagster+ deployments, Dagster+ automatically keeps host processes up-to-date, so no user action is require to achieve this. In OSS deployments, users are expected to upgrade their host processes before upgrading the version of Dagster used in their code locations.
+
+---
+
 ## Python version support
 
 Each Dagster release strives to support the currently active versions of Python.