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GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

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Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#142
post #16

Oh this seems bad, and is fairly easy to reproduce using codex cli. You give it a puzzle prompt that it has to reason about and solve, occasionally it will seemingly short circuit and think for exactly 516 tokens, and return the wrong result. When it ends up using 6000-8000 thinking tokens it returns the correct result. Maybe some issue with adaptive thinking? Another point for local models I guess, don't have to wor…

This is preliminary, but it seems like it might somehow be related to the `## Intermediary updates` system prompt that's provided to the model. Seems like it forces the model to stop thinking and return early to provide updates. Removing that entirely makes all runs succeed [1].

I wonder if it's somehow getting confused between what's supposed to be an intermediate update vs the final result.

[1] https://github.com/openai/codex/issues/30364#issuecomment-48...

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#143
There is nothing called "GPT5.5 Codex" unless I've completely misunderstood OpenAI's product line?

Codex is a harness, while GPT-5.5 is a model. The last codex-branded model was 5.3. Codex as a harness ships as a CLI, a desktop app, and a web product (and I'm not at all sure how similar the underlying harness is between them.)

Is the bug here supposed to be with the CLI harness, or the model? Does it also happen in pi, opencode, etc while running GPT-5.5?

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#144
post #12

Earlier quoted context omitted.

That was an article in The Information but it didn't read very well to me, I didn't get the impression the author was enough of a technical expert on how LLMs work to credibly evaluate the claim, which came from an insider rumor: https://www.theinformation.com/newsletters/ai-agenda/openai-... > OpenAI engineers earlier this month told some colleagues they had figured out a way to more than halve the cost of inference…

I bet that since this bug has made headlines, there are some panicked engineers at OpenAI desperately trying to figure out how to fix it without undoing their “magic optimisation”.

Is there any indication that optimization shipped? Depending on whether it’s R&D or pragmatic, I’d expect it to take months at least.

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#145

A rare case "they made the model dumber" where they actually made the model dumber, instead of the usual user psychosis?

This is the second one in a row now (previous was Anthropic flic in Feb/March)

Nah there have been thousands of “they made the model dumber” false alarms between these two.

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#146

It's funny, they sell you a subscription for frontier models, then over time begin to nerf them rapidly and no one talks about it. Should give me a discount when they reduce reasoning effort silently on the server side! But on the other hand, I've been using 5.5-high on a daily basis in multithreading workflows, i.e. in parallel. I'm barely exhausting my weekly limits. I can't even Human-as-a-Service fast enough to c…

I’ve been paying $200/mo for Claude code for, IDK, 9 months?

I am 100% sure that I get far more value from today than I did in December. The models are smarter, the limits are higher. It’s possible there’s some “five steps forward, one step back” going on, but it’s hard to imagine complaining about that step back.

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#147
post #42

Earlier quoted context omitted.

How do you mean OpenAI lets you use your own harness? I'm under the impression that a custom harness requires the OpenAI SDK, which requires api tokens rather than plus/pro accounts.

https://x.com/thsottiaux/status/2058071172361998482 "A little secret. About 5% of our production traffic is on the Pi harness, about another 5% is on OpenCode. Reminder you can use your ChatGPT account in a flourishing set of other tools. We’ll continue to make Codex awesome, but you have options."

They will only do this while they have no users. Once they are compute constrained they won't let you do this anymore

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#148
post #16

Oh this seems bad, and is fairly easy to reproduce using codex cli. You give it a puzzle prompt that it has to reason about and solve, occasionally it will seemingly short circuit and think for exactly 516 tokens, and return the wrong result. When it ends up using 6000-8000 thinking tokens it returns the correct result. Maybe some issue with adaptive thinking? Another point for local models I guess, don't have to wor…

I have a philosophical problem with adaptive thinking. It’s a dumb guess for how much thinking budget to allocate ahead of thinking. At least in the context of LLMs there is probably no way of knowing how much thinking (token generation) is needed. The problem space is infinity vast, similarly of two prompts is not going to help any LLM decide how much thinning is needed. Models already stop thinking before hitting t…

I agree, adaptive thinking is a pest and without a minimum thinking budget especially Claude for me currently defaults to not think at all even on max effort.

Sequential-thinking was really a step in the right direction, and works almost exactly how you've described, though when it was popular before the reasoning models and even now when I tried it recently I have never once see it use its branching feature and it tends also to have the RLHF urge to answer something "helpful" quickly instead.

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#149

this explains so much why gpt 5.5 has been so bad lately it was really puzzling why it struggled so much where when it first came out it was one shotting stuff totally amazing, i tried the prompt that will tell you if your plan is degraded: codex exec --json --skip-git-repo-check --ephemeral -s read-only --disable memories -m gpt-5.5 -c model_reasoning_effort=high "Do not use external tools. A black bag contains cand…

Verified this locally myself. Thanks for the concrete test. I guess it's time to give Claude another try.

This is preliminary, but it seems like it might somehow be related to the `## Intermediary updates` system prompt that's provided to the model. Seems like it forces the model to stop thinking and return early to provide updates. Removing that entirely makes all runs succeed [1].

I wonder if it's somehow getting confused between what's supposed to be an intermediate update vs the final result.

[1] https://github.com/openai/codex/issues/30364#issuecomment-48...

Re: GPT-5.5 Codex reasoning-token clustering may be leading to degraded performance

#150

There is nothing called "GPT5.5 Codex" unless I've completely misunderstood OpenAI's product line? Codex is a harness, while GPT-5.5 is a model. The last codex-branded model was 5.3. Codex as a harness ships as a CLI, a desktop app, and a web product (and I'm not at all sure how similar the underlying harness is between them.) Is the bug here supposed to be with the CLI harness, or the model? Does it also happen in p…

If the issue comments are to be believed it could be related to the codex system prompt itself so likely just the harness. I agree the wording is weird but they appear to be referencing GPT 5.5 in Codex because yeah there isn’t a GPT5.5 Codex model.
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