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Microsoft Agent Framework dotnet-1.21.0 lands four breaking changes at once, including limiting MCP skill archives to ZIP
The 2026-09-11 .NET release marks four PRs BREAKING: MCP skill archives are restricted to the ZIP format across both .NET and Python (#8290), LocalCodeAct's subprocess environment is isolated (#8159), A2A agent run modes are redefined (#8032), and `file_access_read_lines` moves the line-numbering contract onto AgentFileStore (#7671). LocalCodeAct also picks up OS validation hardening (#8239) and the same approval process Hyperlight already used (#8289), and Hyperlight sandbox fingerprints are now canonicalized (#8295). The release drops the Azure.AI.OpenAI dependency entirely and swaps deprecated AWSSDK.Extensions.Bedrock.MEAI for AWS.Bedrock.MEAI.
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