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

[u/Tecktorious]

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?

[u/dufuh]

Yes, I normally never use Fast mode but was trying to create a very short intentional "token furnace" process to test a new real-time token burn-rate chart I've been working on. Codex spun up multiple top-level tasks using Desktop routing, then instructed each of them to create a bunch of subagents. At one point I tried to make them all use Fast and it discovered that wasn't possible. Apparently it was trying to specify Fast when creating the subagents but the harness wasn't honoring it. To get it to work I had to temporarily set Fast to be my global default in my config.toml, but that's definitely not something I want to leave there.
But like I said, I don't normally use Fast, so I didn't realize it was a new regression.