Claude's Anti-Distillation Rule Turns Your Agent's Message History Append-Only
Book: AI Agents Pocket Guide Also by me: Thinking in Go (2-book series) — Complete Guide to Go Programming + Hexagonal Architecture in Go My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub If your Claude integration rewrites its own conversation history, the API can answer with a 400 that begins…
Claude's new anti-distillation rule requires agents using Claude's API to treat their conversation history as append-only. If an agent's integration attempts to modify or rewrite previous messages in the conversation, the Claude API will respond with a 400 error code indicating an invalid `signature` in the `thinking` block. This rule is part of Anthropic's efforts to prevent other labs from harvesting Claude's reasoning for training their own models, which have reportedly reduced the amount of data harvested by distillers by 90 to 99%.
The rule applies to all multi-turn integrations, affecting how agents handle their conversation history.
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