[Bug] Forced model switching from Claude 5 to Opus 4.8 prevents end-to-end session continuity

Bug Description
Subject: Fable 5 has become unusable for real work — forced model switching and severe quality regression I'm a paying customer building several production projects with Claude Code, and I need to be blunt: something has gone badly wrong with Fable 5, and with the Claude 5 family in general. 1. The forced switching to Opus 4.8 makes Fable 5 unusable. Across multiple projects, my sessions constantly get switched away from Fable 5 to Opus 4.8. I cannot build my own projects with Fable 5 end-to-end, I cannot test with it, I cannot harden anything with it, because I never get to keep the model I chose. Whatever capacity or routing logic is behind this: from the customer's side, the product "Fable 5" has effectively become unusable. A flagship model I can't actually use is not a flagship model. 2. Severe regression in task execution since release. I don't know what has been changed under the hood since Fable 5 first shipped, but the difference is dramatic. At release, Fable 5 was outstanding — especially in strategy, which was its single biggest advantage. Today: - After two or three tasks it drifts massively — losing the goal, changing scope on its own, ignoring standing instructions. - Error correction, which worked at release, no longer converges. It loops, guesses, and repeats the same failed approaches. - Strategy quality, formerly its greatest strength, has become genuinely poor — full of mistakes and drift. - Opus 5 shows the same pattern: bad at working through tasks reliably. The overall impression: the current Fable 5 feels worse than Opus 4.8. That is not what "our most intelligent model" should feel like. The consequence: I now do about 90% of my work in Codex with the 5.6 model. It does exactly what I need: no drift, clean execution, and it actually arrives at a solution. I'm not saying this to promote a competitor — I'm saying it because it's the measurable reality of my daily work. I'm writing this as a genuine Anthropic fan. It honestly hurts to watch these models drift into unusability. I want Claude to be my primary tool again. Please take this seriously: whatever was changed after the initial Fable 5 release is heading in the wrong direction. Reference from a current failing session, in case it helps: ofid_d3105bfce8431726

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.220
• Feedback ID: ca37d7f2-fcdb-46b0-9b58-f26f42258e79

Errors

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