Cannot See Chain Of Thought / Missing Thinking Tokens

[AlexanderJohnston]

🏷️ Discussion Type

Bug

💬 Feature/Topic Area

Copilot CLI v1.0.27

Body

First it started with Opus-4.6 where I could no longer see Chain Of Thought in the GH CLI. As of yesterday, I can no longer see GPT-5.4 chain of thought in the CLI. I did try hitting ctrl+T several times.

I'm using GPT-5.4-xhigh and Opus-4.6-high as examples.

Is this a bug? Is it on purpose? CoT monitoring was the core part of my workflow to catch and avoid misalignment early.

Anyone else experiencing this?

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[AlexanderJohnston]

I am also seeing degraded performance from these models without their Chain of Thought. I'm not sure if that's a nocebo effect in my head or not, but GPT-5.4-xhigh is struggling to understand basic C# apps that it absolutely dominated on just a week ago.

And unfortunately without Chain of Thought, I'm completely unable to figure out why the performance is degrading.

e.g. this failed to actually produce a working C# app to parse a log file. It messed up on basic issues like escaped JSON. As you can see, no thinking tokens are showing.

[AlexanderJohnston]

Here is a session that I haven't closed since last week, when thinking tokens were still available. In this session, gpt-5.4-xhigh is available and it produces thinking tokens.

I am able to continue sending requests to this session and it continues to give me thinking tokens even a week later.

Here is an example of it still producing thinking tokens as of today:

But if I open a new session, xhigh is gone, and thinking tokens are gone:

[AlexanderJohnston]

Last comment I will make on this topic. xhigh works correctly in VSCode on the same account. This is an issue with GH Copilot CLI.

[AlexanderJohnston]

As of today, Opus-4.6 thinking tokens are showing up again.

GPT-5.4 thinking tokens are not showing up. GPT-5.4-xhigh still does not show in CLI v1.0.29

I can only assume this is some serious issue on the backend and the GH Copilot team will eventually fix it.