[Bug] Model unexpectedly switches back to Opus without explanation

Bug Description
why... keep going back opus, at least gimme a reason brother

Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.1.170
• Feedback ID: 3c2344d3-b55e-47ed-940f-89188e1bf9e2

Errors

[{"error":"Error: 404 {\"type\":\"error\",\"error\":{\"type\":\"not_found_error\",\"message\":\"Claude Fable 5 is not available. Please use Opus 4.8. Learn more: https://www.anthropic.com/news/fable-mythos-access\"},\"request_id\":\"req_011CbzZcQTJ8sstArskjGvBf\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:68217)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-13T03:39:05.761Z"},{"error":"Error: 401 {\"type\":\"error\",\"error\":{\"type\":\"authentication_error\",\"message\":\"Invalid authentication credentials\"},\"request_id\":\"req_011CcGbwded72nXm6n3SD3WA\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:68143)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-21T14:59:11.874Z"}]