Hi @zhaoxi2000,
This is expected behavior. When you select Opus 4.6, that model is used for the main agent. Subagents (Explore, Browser, Bash) that get automatically spawned during agent tasks use Composer 2 by default. Your Opus 4.6 requests are routing correctly for the primary agent work.
To have subagents use your selected model instead of Composer, enable Max Mode in the chat settings. More details in this related thread where a staff member covers the workaround options.