Pro Plan Opus Default Option

What: New experimental feature that allows Pro plan subscribers to use Opus 4.5 as their default model.

How it works: When enabled via the tengu_opus_default_pro_plan experiment, Pro plan users will see "Opus 4.5 · Most capable for complex work" as their default model option.

Details:

• Controlled by experimental flag tengu_opus_default_pro_plan with variant opus_is_default
• Added VI6() function at line 181554 that checks if the user's plan is "pro"
• Added haA() function at line 181569 that checks if the Opus default experiment is enabled
• Model description function uaA() at line 181634 now includes the Pro plan Opus option check