jumploops
6 hours ago
Interesting, the new model's prompt is ~half the size (10KB vs. 23KB) of the previous prompt[0][1].
SWE-bench performance is similar to normal gpt-5, so it seems the main delta with `gpt-5-codex` is on code refactors (via internal refactor benchmark 33.9% -> 51.3%).
As someone who recently used Codex CLI (`gpt-5-high`) to do a relatively large refactor (multiple internal libs to dedicated packages), I kept running into bugs introduced when the model would delete a file and then rewrite in (missing crucial or important details). My approach would have been to just the copy the file over and then make package-specific changes, so maybe better tool calling is at play here.
Additionally, they claim the new model is more steerable (both with AGENTS.md and generally). In my experience, Codex CLI w/gpt-5 is already a lot more steerable than Claude Code, but any improvements are welcome!
[0]https://github.com/openai/codex/blob/main/codex-rs/core/gpt_...
[1]https://github.com/openai/codex/blob/main/codex-rs/core/prom...
siva7
4 hours ago
So you're all saying suddenly codex cli w gpt 5 codex is better than claude code? Hard to believe
jumploops
4 hours ago
Not suddenly, it's been better since GPT-5 launched.
Prompting is different, but in a good way.
With Claude Code, you can use less prompting, and Claude will get token happy and expand on your request. Great for greenfield/vibing, bad for iterating on existing projects.
With Codex CLI, GPT-5 seems to handle instructions much more precisely. It won't just go off on it's own and do a bunch of work, it will do what you ask.
I've found that being more specific up-front gets better results with GPT-5, whereas with Claude, being more specific doesn't necessarily stop the eagerness of it's output.
As with all LLMs, you can't compare apples to oranges, so to clarify, my experiences are primarily with Typescript and Rust codebases.
drob518
7 minutes ago
Yea, I have struggled with Claude to keep it focused on what I want and only what I want. I have no experience with GPT-5-Codex, but maybe I should.
srcreigh
3 hours ago
Codex CLI of course will sometimes do the wrong thing, or sometimes do something extra that you didn't intend for it to do.
It seems about half my sessions quickly become "why did you do that? rip __ out and just do ___". Then again, most of the other sessions involve Codex correctly inferring what I wanted without having to be so specific.
j45
an hour ago
Sounds like the difference between finding what needs to be done, making a plan, and executing on it remains something to consider and be aware of.
Claude Code has been a revelation and a bit of a let down the past 45 days.
Some open acknowledgement would have been great, but in lieu of it, it seems it's best to hop on a new tool and make sure you learn how to prompt better and not rely on the model to read between until usage is "optimized" and it no longer seems to work for those folks.
I've seen some interesting files that help any model understand a programming language as it's strong suit and it might not even be an expert in and how to best develop with it.
wahnfrieden
3 hours ago
It is 100% true. And they are rapidly losing users to Codex. Charts were shared recently showing a massive migration underway.
tedsanders
6 hours ago
> SWE-bench performance is similar to normal gpt-5, so it seems the main delta with `gpt-5-codex` is on code refactors
SWE-bench is a great eval, but it's very narrow. Two models can have the same SWE-bench scores but very different user experiences.
Here's a nice thread on X about the things that SWE-bench doesn't measure:
pants2
6 hours ago
Interestingly, "more steerable" can sometimes be a bad thing, as it will tend to follow your prompt to the letter even if that's against your interests. It requires better prompting and generally knowing what you're doing - might be worse for vibe-coders and better for experienced SWEs.
jumploops
4 hours ago
Yes, given a similarly sparse prompt, Claude Code seems to perform "better" because it eagerly does things you don't necessarily know to ask
GPT-5 may underwhelm with the same sparse prompt, as it seems to do exactly what's asked, not more
You can still "fully vibe" with GPT-5, but the pattern works better in two steps:
1. Plan (iterate on high-level spec/PRD, split into actions)
2. Build (work through plans)
Splitting the context here is important, as any LLM will perform worse as the context gets more polluted.
Turskarama
28 minutes ago
The best of both worlds would surely be for the LLM to write what you've asked, but also write comments about other things it could have done so you can consider those extra bits when you check the output.
htrp
6 hours ago
think they're indexing here for professional work (people in the VSCode terminal)
j45
an hour ago
I wonder if this means part of the prompt has been moved to a higher level somehow... or baked into the bread elsewhere.
groby_b
2 hours ago
Small suggestion on refactors into packages: Move the files manually. Just tell codex "they used to be in different locations, fix it up so it builds".
It seems that the concept of file moving isn't something Codex (and other clis) handle well yet. (Same goes for removing. I've ~never seen success in tracking moves and removes in the git commit if I ask for one)
artemisart
an hour ago
Does refactoring mean moving things around for people? Why don't you use your IDE for this, it already handles fixing imports (or use find-replace) and it's faster and deterministic.
jumploops
44 minutes ago
Not necessarily -- in the case I posted about, we first abstracted some common functionality to internal libs, and then further abstracted that functionality into a number of packages (so they could be used by other clients).
So it was part simplification (dedupe+consolidate), and part moving files around.
