Opus 5 fails reasoning tasks; Fable steps in with clarity
MakesNotSense · reddit · 2026-08-21
A developer compares Opus 5 and Fable models within an agent harness workflow.
- Opus 5 Failures: The model repeatedly failed to follow protocols (e.g., checking upstream fixes), hallucinated false premises, and persisted in building logic upon them. It struggled to comprehend or apply a "check the premise" protocol despite explicit instructions and feedback.
- Fable Success: Switching to Fable resulted in immediate comprehension of the scientific method's importance (challenging hypotheses) and clear communication.
Takeaway: Significant capability gaps exist between models regarding complex reasoning and adherence to first principles in agent workflows.
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