Did the new API/model setup stop passing Fast mode to child agents?

Has anyone else noticed this after moving to the newer API/model setup? I’m using GPT-5.6 Sol with child/subagents v2. When I asked one of the child agents to enable Fast mode, it told me that it doesn’t have a Fast mode option available — it only sees the model and reasoning/thinking settings. From what I can tell, OpenAI still supports Fast mode through service_tier , so I’m wondering if the issue is actually with the API/wrapper/orchestration layer not forwarding that parameter to child agents. We recently changed the API setup, so I’m trying to figure out whether: service_tier is no longer being inherited by child agents it has to be explicitly passed on every child request or the new API layer simply doesn’t expose it Has anyone run into the same thing with GPT-5.6 Sol/subagents?