Why GPT-5.4 agent is using Claude Haiku 4.5 model in VSCode Copilot?

[HermesZum]

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I started using the GPT-5.4 agent in Copilot. Shortly afterwards I noticed that the agent was using Claude Haiku 4.5 models. How is it possible? Is it a bug or is it real?

[WattoX00]

It is not a bug.
Copilot agents can route some subtasks to other models for things like file scanning, repo reading, or summarization, while GPT-5.4 remains the main agent controlling the workflow.

[HermesZum]

I didn't know, as I've never seen this happen in GPT-5.3-Codex, I was surprised. Thanks for the update.

[HermesZum]

I have used this delegation of functions for other inferior models on the part of GPT-5.4. From what I've seen this method makes everything slower. Nothing useful for performing tasks. I don't see the use of this function at all. I disabled it to make the work faster.