Sep 26, 2026 · Backend Development

DeepSeek Harness Session V4: Tool Result Restructure, Source Identity & Migration Impact

This article details the major data structure changes in DeepSeek Harness Session V4, including tool/result message restructuring, source.kind identity model shift, new developer/message surface type, dynamic tool history via headerSeq, deferLoading schema support, and migration rules affecting plugin authors and session parsers.

DeepSeek HarnessDeveloper MessageDynamic Tools

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DeepSeek Harness Session V4: Tool Result Restructure, Source Identity & Migration Impact