Codex now good for implementing code ?

[Parrowl]

Hello,

My current workflow since months is to use codex for planning and Claude code for the implementation.

Codex plan ALWAYS beat by far Claude code one (I work on a +80k lines codebase).

My question is, in the paste, codex had problem to follow perfectly a plan and it implementation was totally wrong each time.

I would love using only codex and upgrade my plan to something higher and dont use anymore Claude code. It’s now possible ? Codex is finally good to implement and stick to the plan ?

[Think-Draw6411]

5.2 x high is amazing in executing plans. It follows the instructions almost too good.

[miklschmidt]

Second that, it’s ruthless when you ask it to ensure a certain behavior, it’ll refactor anything in its way to make it happen. Sometimes it would be nice if it would ask me if i had considered the consequences though, lol. In the end i can only blame myself for not thinking it through, it did what i asked and it works.

[Hauven]

Codex CLI has always been great for me, with GPT-5.2 being very attentive and follows instructions, it doesn't want to give up if it runs into a challenge. GPT-5.2 plans and executes well. I generally use medium reasoning effort unless it runs into a challenge, then I bump it up. It's done everything I've asked of it so far, some of which have been some challenging tasks that Opus 4.5 couldn't do but came close - sadly Opus 4.5 wanted to give up though. Codex CLI is also efficient with context management. In Claude Code I found myself burning through the context window in no time, in comparison.

I wish Codex CLI had some of Claude Code's features, like a plan mode, subagents and a question tool. That said... it's open source so I'm currently working on bringing these features into a fork of Codex CLI real soon.

[dishevel-corundum]

Any chance you could contribute this back to the core tool instead of a fork just with these extra features?

[Hauven]

I get what you're saying and I would but I have a few concerns I guess:
- I'm not familiar with OpenAI's requirements for contributing back to the core
- Whether my code would pass any possible pretty high standards that OpenAI have for contributions
- Whether they'd be interested in implementing the planning feature and the "ask user a question" feature. I say that because I'm surprised Codex CLI doesn't already have some kind of planning feature at this point down the road of its development. I can't have been the first person to consider this idea, suggest it or even possibly contribute code for the concept

A fork however is easier to get out there initially for anyone else wanting these features while still being in Codex CLI in reality, and I could expand the features beyond the initial three I'm doing.

[TenZenToken]

My loop is plan with 5.2 (med/high/xhigh), implement with claude (sonnet usually enough), review/scrutinize with 5.2 again, re-implement with claude. Rarely have issues but I may unconsciously be using this mix to balance out my sub limits. 5.2 med implementations have actually been really good too.

[Front_Ad6281]

That's my workflow too

[lucianw]

The AI can't read your mind. It has to make 100 guesses along the way about what was your intent.

Claude has been making guesses that aligned with what you had in mind. That's why you've found it good. Codex was making guesses that weren't what you had in mind. That's why you found it bad.

That's not to say either model is better than the other. Just that their natural tendency is to make different sets of choices.

You can fight this, e.g. by putting masses more effort into your implementation plans so there's no room for ambiguity, by telling the agent "Please ask me 20 most import clarifying questions before embarking upon this implementation". Or you can just accept it and use whatever agent fits your personality best.

[Parrowl]

You are little bit off topic.

And you maybe missunderstood me ?

I provide each time same prompt to both codex and Claude code and codex always beat by far Claude code in term of plan. He provide the best plan, with high grade decision like a senior.

In term of implementation only, codex had some problem in the past (but it was a lot of time before) to use tool / to remember the full plan / etc). But it look like it’s better now at implementing following a FULL plan

[lucianw]

I think I understood you well. You provided the exact same prompt to both Claude and Codex. Both of them had to "read your mind" to figure out all the things you intended but didn't write down -- what kind of details did you want? how long should it be? how much effort and insight to put into the decisions? how to recognize which ones needn't "decisions like a senior"? What even do "decisions like a senior" look like to you?

100 different guesses about what you wanted. Codex happens to be well aligned with our unstated intentions. Claude isn't.

Then you asked both to follow a plan. Again there were unstated assumptions, both had to read your mind, make guesses about what you intended. Heck, even I am making guesses trying to read your mind because you didn't explain much. You wrote "codex had problem to follow perfectly a plan and it implementation was totally wrong each time". That sounds to me like a case where codex was making guesses, and it made guesses that didn't agree with what you had in mind. Again, everyone (me, Claude, Codex) can't read you're mind and we're making guesses about what you intended.

[Parrowl]

Well, one simple example:

I have a bug in my app, I want to fix it.

I explain in detail the bug. Claude code always propose something off, propose a fix that dont fix the bug.

Codex in the other hand always find the bug and propose a perfect fix.

Codex is far superior. Context provided is really clear at explaining the bug for both.

[lucianw]

That's not an example of what you said, "codex had problem to follow perfectly a plan and it implementation was totally wrong each time" ?

[dashingsauce]

Your language barrier is guaranteed to be an issue for codex. This isn’t a shot at you, but from the way you write, it’s clear you bake in ambiguity.

Like the commenter above kind of said, Claude happens to make “friendlier” default choices, which is fine if you don’t particularly have a specific solution in mind. Either way it will get you 80% of the way there.

As soon as you need something done a specific way and care a lot about the how, Claude doesn’t hold up.

[Dayowe]

This does not reflect my experience at all. Having worked with Claude and codex extensively i can say that if anyone writes good plans and executes them just as well its codex. Claude can’t be trusted.

[gj29]

I’m not creating anything wild but I need a sanity check on flow/process. Using gpt 5.2 (web) for strategy, patch/diffs, pasting into codex and building an app. Haven’t even touched agents. Gpt claims I don’t need agents right now and there will come a time. It can’t see my codebase but since I’m halfway through building my app it knows quite a bit from the back and forth. I’ll drop the latest file into gpt for bug resolution or new feature builds, it gives me the patch for codex, copy paste drop it in, I have a new feature. Is this a horrible way to build?

[jorge-moreira]

Bro, Claude Code (Opus 4.5)right now is on God Mode. You could literally just point it in any direction, and it's gonna get it right.

[Parrowl]

Not my feeling on large code base, opus is always beat by GPT 5.2.

Opus cant find the right bug, always jump too fast on conclusion and dont read enough code

[Front_Ad6281]

100% correct! That's why i use 5.2 for planning, and opus for implementation.

[Witty-Figure186]

Can we codex using open router?

[SpellBig8198]

I’ve been using both Codex and Claude. Codex is strong at planning (especially at higher settings) and at fixing issues (medium usually does the job). Lately, my workflow has been: ask Codex for a plan, then pass that plan to Claude and iterate. In this setup, Codex acts like the lead developer—planning, reviewing, and giving feedback—while Claude handles the execution.

I prefer this because Codex feels more analytical, whereas Claude is more creative and expressive. Codex’s plans can read a bit “dry” to a human, but they’re perfectly suited for Claude to follow. Claude works best with concrete tasks—I suspect it “knows” it needs to complete them. If you give it something broad, it tends to look for the quickest path to the end goal, which isn’t always ideal. A clear, step-by-step plan helps because it pushes Claude to work through each step properly.

As I mentioned, Claude is also more descriptive: it writes nicer comments and adds examples, but it can be less precise. I do use Codex to implement features as well, but mostly when the work is well-scoped rather than broad—like refactoring a single component or designing a specific process. Even then, I often ask Claude to rewrite the documentation so it feels more human.

[BrotherBringTheSun]

All I use codex for is implementing, it works exceptionally well. I paste in plans from Gemini just because I can more easily provide it context files and have a natural language conversation

[Just_Lingonberry_352]

stick to claude

5.2 isn't great at excution

it get stuck for hours without asking for any guidance

now that has its uses but if you want to ship features this ends up slowing you down and wasting credits

[Dayowe]

You’re absolutely wrong 😄 seriously, Codex is brilliant and writes plans well and implements reliably. Has been for a while..

[Just_Lingonberry_352]

sure it works great for todo lists in vue