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platform-support.md

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+# Platform Support Lifecycle
+
+"Platform Support" for this project includes three somewhat different things:
+1. The target platforms for which tests may be written.
+2. The platforms under which those tests will run, which is equivalent to the list of agents we supply.
+3. The minimum platforms required to execute the runner and engine themselves, without regard to the tests being run.
+
+## Test Assembly Target Runtimes
+
+We will continue to support tests targeting runtimes which are out of support from Microsoft's perspective, so long
+as we are able to do so without significant additional effort or security risk. If no agent is available for a runtime,
+the tests will be run on the closest higher runtime available.
+
+> _We currently support execution of tests written to target any version of the .NET Framework >= 2.0 and any version
+> of .NET Core >= 3.1, including .NET 5.0 and higher._
+
+## Agents Provided
+
+We will continue to provide agents for any Microsoft runtime for at least six months after its end of life. This is 
+intended to support continued testing of legacy applications while users are in the process of upgrade. However, agents
+for runtimes which have been declared a security risk may be removed immediately.
+
+> _We currently supply agents for .NET Famework 2.0 and 4.6.2. .NET Core 2,1 and 3.1 and .NET 5.0, 6.0 and 7.0. The .NET
+> Core 2.1 runner is being removed in version 3.18.0 and .NET 8.0 will probably be added before this document is finalized.
+> Once this document is approved, we will begin to phase out agents according to the above criteria._
+
+## Required Runtimes
+
+The console runner and engine target .NET 4.6.2, so that runtime or greater is required to execute any tests at all
+without loss of features. In individual cases, it may be possible to run using a lesser version of .NET 4.x.
+
+> **Note:** Editorial comments in italics will be removed in the final version of this document