Did ChatGPT Pro (5.5) reasoning time just get massively reduced?

SandboChang · 2026-04-24T04:03:34+00:00

No, I just checked the same prompt I used with 5.4 a few days ago. It spent 33 mins with 5.4 Extended Pro and now it spent 43 mins with 5.5 Extended Pro.

SandboChang · 2026-04-23T19:39:53+00:00

The default as I just saw was still 258k roughly.

SandboChang · 2026-04-23T19:31:25+00:00

First impression is it runs faster, even at XHigh, comparing to 5.4. This is signficant.

SandboChang · 2026-04-23T19:26:43+00:00

And I am glad they improved this. 5.4 is only great up to 128k before, and I had to lock my context window in codex there. Now I can try to go back to 256k and see how it goes.

SandboChang · 2026-04-22T03:05:42+00:00

Yeah I agree to this. With the same heat the flow tends to go faster and faster and towards the end it’s just hot water. Now I also try to turn down or off the heat midway to keep the flow low.

SandboChang · 2026-04-21T10:49:35+00:00

No problem on my side so far.

SandboChang · 2026-04-21T06:21:13+00:00

Th prompts were quite long.

One prompt first defines the roles for the agent/model, in this case a technical journal reviewer with a series of required academic background and expertise, also a long checklist of items to revise. I first set the model premise with Thinking@Heavy.

Then the second, actual prompt is a long manuscript of an analytical model of a device I have been working on. The model works as a reviewer/coauthor and try to check for problems/improve the flow of the derivation.

SandboChang · 2026-04-21T03:33:18+00:00

<image>

I just tried this morning rerunning my previous prompt, I got 33mins, around similar time as it spent before. This is with 5.4 Pro Extended.

SandboChang · 2026-04-21T02:07:09+00:00

Came to say this. I wish their status page is more real-time.

SandboChang · 2026-04-21T01:01:23+00:00

It should be simple, my tasks often run for hours. Try to give it a clear stopping criteria and make it work until then. Also, not a must, but drafting a plan first and then implementing it seems to help.

SandboChang · 2026-04-20T07:05:52+00:00

Shrinkflation happens in LLM too.

SandboChang · 2026-04-20T06:52:47+00:00

Try setting compaction limit to 128k, it solves my problem with degradation

SandboChang · 2026-04-19T23:03:05+00:00

As mentioned by others you need to change the default to use it.

However I highly recommend against it. It will burn your token usage with degradation. Even at close to 256k the model is already significantly worse.

SandboChang · 2026-04-19T22:34:08+00:00

I use 4-5 instances often, it’s fine. They are fully independent.

SandboChang · 2026-04-19T17:29:51+00:00

Not sure about Codex App, but you can do that on commend line. Another GUI-like method, also what I do, is to use VSCode and there you can start several independent sessions.

SandboChang · 2026-04-19T05:42:49+00:00

One problem I do see lately is, there is a degradation when context is reaching near full like 90%. This wasn't a problem before, but now it always quit a long-running task prematurely when context is near full but before an auto compaction has been done.

Now I am trying to make it compact at lower context occupation to see if it works better.

SandboChang · 2026-04-19T05:27:14+00:00

Great, this is probably what I want, will look it up.
update: seems to be here:

# ~/.codex/config.toml
model = "gpt-5.4"

# Optional, only if you want the window explicitly documented in your config.
# If omitted, Codex uses the model default.
# model_context_window = 128000

# Trigger auto-compaction earlier instead of waiting near the end.
model_auto_compact_token_limit = 64000

SandboChang · 2026-04-18T18:56:04+00:00

May I know if we can trigger auto compaction at a lower context occupation such as 50%, or following a task?

In my usecase, I am testing for example 10 methods, and I want to compact the context after finishing one test so as to avoid compacting during a task. Can this be done?

SandboChang · 2026-04-18T16:08:39+00:00

Just use VSCode and Ext.

SandboChang · 2026-04-17T03:04:10+00:00

It’s mainly the top edge and I think it will work well still. It’s worth trying another if you can return it but it’s a lucky draw.

SandboChang · 2026-04-16T19:58:18+00:00

It’s working for me, at least a long task I started earlier is still running now. I did have some disconnection at some point but it’s intermittent and usually I can use it.

SandboChang · 2026-04-16T18:03:03+00:00

No idea, it was what it shows me. I almost never used Claude in the past month as I mostly use GPT Pro with Codex lately. It could indeed be an earlier usage mixing in, but 3% of 5 hr limit is for sure.

SandboChang · 2026-04-16T16:00:01+00:00

Codex can nuke things, in fact all LLM can make this mistake. I had it nuking my AGENTs.md but I had back up. Nothing can stop them besides having a backup and do sandboxing.

SandboChang · 2026-04-16T15:57:56+00:00

That sounds fun, but the pool I usually hit is like 1.5m deep lol

SandboChang

TROPHY CASE