Vibe Coding
Pattern: an Anthropic default-model flip now propagates through the whole tool chain inside 24 hours
Fable 5.1 shipped on 2026-09-01 and by 2026-09-02 it was the default in Claude Code 2.1.257, the resolved default for 57 providers in Cline v4.1.17 and 36 in Cline Desktop v0.0.22, and a supported model in Copilot CLI v1.0.83-2, while opencode v1.18.26 shipped a compatibility fix for its thinking-block behavior. The practical consequence for builders is that not pinning a model in any of these tools means your agent silently changed models overnight, and Fable 5.1 has documented behavior differences in tool batching and file editing that will show up as changed token spend before they show up as changed output.
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