A new sent-prefix ledger, tracked per conversation, compares each outgoing request against what was previously committed to detect a model switch, a declared boundary, or a violation. When a tool description, input_schema, or system-prompt section has changed since it was first sent, it synthesizes a diff block for the model prefaced with: "The following changed since it was first sent in this conversation. The earlier text above stays as sent; where they differ, the current version below is the one in effect."
New mid-conversation tool/system-prompt diffing sent to the model
When a tool description or prompt section changes mid-conversation, Claude is now sent a diff saying the newer version is in effect.
You'll noticeTier: how much it should matter to you
4Useful: my rating, 1 to 5
4Signal: worth watching, 1 to 5
System PromptArea: what it touches
ImprovementsKind: in v2.1.257,
What probably matters to youSection of the release