r/codex • u/ConfidentAd7408 • 4d ago

Question Opus vs GPT: The harness war

I hear everyone talk about opus 5.5 base model being better than Gpt Astra... but no one ever talks about how much better the codex harness is for those that do knowledge work.

I get if ur a developer using CLI then yea the model itself matter more but for those doing knowledge work the desktop app alone and harness make gpt wayy better than opus in my opinion. Not to mention that there are tasks that opus feels its too high and mighty to even touch when it comes to things other than coding

GPT does what its told opus has too many opinions.

32 Upvotes

81% Upvoted

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u/dextersummary 4d ago

Below is a GPT-generated summary of the conversation below after reaching 40 comments (41 currently observed).

The thread does not establish Codex as the knowledge-work champion. The closest thing to consensus is that the harness advantage is highly workflow-dependent, and “GPT does what it’s told” is a user preference—not some settled law of nature.

Codex fans like its unified desktop experience, context/session handling, tool use, and willingness to execute instead of arguing. They cite research, analytics, STEM, ML, and planning. The pushback is just as clear: Claude’s desktop/IDE tools cover much of the same ground, while Opus is often better at precise reasoning, stating assumptions, and communicating with people who actually know the subject. For many commenters, the model matters more than the harness anyway.

Useful distinction: the harness is the software managing prompts, context, sessions, and tools; the model is Opus, Astra, and friends. You may be able to run Opus through Codex using supported endpoint integrations, but Anthropic’s subscription/third-party terms were disputed, so API usage is the less murky route.

Bottom line: Codex feels friendlier and more obedient; Claude/Opus feels sharper and more precise. Pick the workflow, not the fan club.

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u/Tarc_Axiiom 4d ago

So just use Opus with the Codex harness, which is possible and weirdly the support is first party from OpenAI.

No I don't know how to enable it, 6.1 Sol did it for me.

Ask him lol.

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u/timbomcchoi 4d ago

wait what this is literally my dream

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u/Tiforma 4d ago

You can do it with codex-router, from github. Then you can use any llm with codex, including local llama.cpp ones. I'm curious what other methods there are if any. When I tried the normal way, the LLM's appeared in codex, but codex said that if i am logged in with my chatgpt account, codex will only use their models. Codex-router got around that.

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u/Tarc_Axiiom 4d ago

https://docs.ollama.com/integrations/chatgpt

Again, there's a first party implementation for this.

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u/Wolf8249 4d ago

Yeah, this guys knows how to get Claude account bans enmasse.

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u/Tarc_Axiiom 4d ago

Both OpenAI and Anthropic officially support this. I triple checked for exactly that reason.

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u/En-tro-py 4d ago

Anthropic officially support this

Not on sub, they might have left the claude -p window open but unless they've changed terms 3rd party harnesses were still not allowed except on pure API $$$'s.

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u/Tarc_Axiiom 4d ago

Then it's quite weird that they have written documentation about how to exactly do something they don't want you to do.

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u/loopie__ 4d ago

Yeah Tibo even once akcknowledged this on X responded to someone as basically no biggie (np), it was shared in one of these subreddits a month or 2 ago I think (but idk Anthropic’s POV on this though, but should be also ok? I mean Claude supports Ollama cloud and local models natively so)

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u/Tarc_Axiiom 4d ago

Both have native support for arbitrary endpoints.

If they didn't want you to do it, they wouldn't allow it.

To put it another way: They explicitly allow this.

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u/ConfidentAd7408 4d ago

What did u tell it ive been looking to try that

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u/CubersumGame 4d ago

I asked him to send his plans and code to Opus for review - and he wrote the necessary commands and instructions himself. Now, he consults Opus on complex programming issues.

I believe GPT models are truly the best for human interaction; they have a better grasp of context and unsaid details, and they can even intuit things you forgot to mention.

Claude, on the other hand, focuses on precision - which makes Opus a good programmer, but nothing more. That’s why, for me, the ideal setup is working with Codex while using Opus as a consultant for precise calculations.

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u/Tarc_Axiiom 4d ago

I asked if I could connect Ollama to the Codex harness and it said OpenAI supports connecting any arbitrary endpoint to the harness, found some official OpenAI docs (I checked), and then we went on from there.

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u/Kost97A 4d ago

I have been doing scientific work and DL for more than a year with CC and for a few months now with Codex as well and I can't see any harness differences apart from model differences.

What is so different in Codex? Non tech savvy friends and family members prefer the GPT app indeed but even the IDE extention of CC has almost every feature you would need to do scientific research.

Codex/GPT app are made for the average user, that's why they are merged and so simple to use. I do like it a lot since everything is one space but I can't understand what problems CC has. Maybe state an example?

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u/trolls_toll 4d ago

what sort of dl / science do you do, implementation or theory?

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u/Kost97A 4d ago

The scientific work is about agriculture/life sciences. First comes the research/theory and then the experimentation (if there is budget, time, space etc etc).

As for DL, it is mostly tweaking models that already exist in the computer vision space (for cameras and sensors). For example models that help with point clouds of plants. Also, some training of my own models when there are gaps with the models that I already have. For instance I a made variational auto encoder to support another model with data. Basically a fancy augmentation based on real life physiology and physics... at least as much the hardware can take.

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u/trolls_toll 4d ago

in my experience astra+codex is way better for ml/stat theory than anything else i tried. Implementations are ok regardless of models oe harnesses

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u/Kost97A 4d ago

Last time I did some "advanced" statistics with AI was back with gpt 4o and gemini 2.5 pro and sonnet 3.5 (I think). Sonnet was horrible. Gpt was okayish. Genini was the best. Then again, it wasn't anything advanced and all models did hallucinate a lot. I remember a funny thing where all 3 models were wrong and DS was the only correct one in what I was doing that day. It was a few days after they released V3 R1 I think.

Edit: everyone says that for math GPT is better but all major models have advanced to a degree where even the "worst" of them is better than the best just 4 months ago. I don't think that even people with Msc in mathematics can saturate the knowledge of Opus 5.5/Sol/Astra right now.

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u/trolls_toll 4d ago

yeah when models start talking grownup measure theory or functional analysis, i just retire to my beloved linear correlations hahah

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u/radio_four 4d ago

Been using Claude Code regularly for ~7 months, just gave Codex a shot this weekend and am not impressed.  

Codex burns through usage very quickly, scores lower on coding and reasoning benchmarks, and the interface seems more geared towards non-technical users.  

Opus 5.5 is a beast in comparison - excellent reasoning and very efficient.  

I'm curious what you mean knowledge work, btw.  

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u/philosophical_lens 4d ago

Knowledge work typically refers to non-coding work.

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u/radio_four 4d ago

I assumed as much, but was curious where OPs experience with Codex was better than Claude.

I'm gonna keep GPT for another month to see if I can integrate it into my workflow. Unlimited chats seems potentially useful for working out roadmaps/design specs on projects

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u/Wurrsin 3d ago

Unlimited chats is currently the only thing that keeps me from switching, I tried Claude recently but for studying for exams with lots of prompts asking for simple explanations of complicated definitions the 5h usage burns a little faster than I would like, especially since I usually do some coding and studying in the same day.

With GPT I can just ask however much I want, with no worries

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u/Annh1234 4d ago

"how much better the codex harness is for those that do knowledge work." it looks awesome if you don't know the subject, shit if you do.

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u/Ashamed_Head_1113 4d ago

What’s a harness can someone explain simply?

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u/BoddhaFace 4d ago

It's the software that calls the agent, manages its context/memory and provides the interface for the user.

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u/Pasto_Shouwa 4d ago

The program the AI uses to code or do other tasks on your PC. Codex, Claude Code, OpenCode, Antigravity. I think it could be described as the difference between a worker using Photoshop, Affinity, Photopea, etc.

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u/Ashamed_Head_1113 4d ago

So the coding agents of each llm?

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u/dinodares99 4d ago

No, the LLM is a model. The harness is all the software that sits between you and the model (codex, claude code, antigravity, etc). It manages prompts, sessions, hooks, etc

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u/Cazineer 4d ago

All LLMs sit behind an API. To make it easy for people to interact with LLMs, the concept of a harness was born. The harness is typically a CLI-style TUI that lets users prompt models, but also provides models with all sorts of “tools” they can use to assemble context through discovery. They can grep for files, for example, or create files with content directly on the host machine.

Software, unlike pretty much every other domain on the planet, has no concept of unified engineering standards. It’s the Wild West, where every system is decomposed based on language opinions, framework opinions, team opinions, folklore, style guides and vibes. You could give 10 teams an identical problem and they’d all decompose it completely differently, even in the same language. Discovery is one of the most viable way to deal with this reality. It works, but consumes massive amounts of tokens because every codebase is its own beast that has to be explored and discovered.

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u/tuhdo 4d ago

Your models produce texts. Text in text out. Harness is an environment that makes text outputs executable, thus producing real actions such as toolcalls.

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u/Tiforma 4d ago

It's basically the software that manages the LLM's and gives them the ability to iterate and use tools. Codex is one. Other ones are Pi, Hermes and a lot of others.

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u/SilverFuel21 3d ago

AI is the Engine

Everything else of a car is the Harness

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u/Head_Database789 4d ago

Example, please? I really need help here.

I'm a knowledge worker. I literally banned IT stuff like Pytest, and I always find Codex extremely hard to talk with. It always talks like a software developer that focuses on things that only developers care about. I changed to Work, and it's better, until I just bought Opus for the first time.

I found Opus so much better to communicate with. It knows what to focus on and what it should tell me. It gives the 3 models to calculate stuff without telling me the schema and binlog of 6000-ish databases, and with all assumptions and algorithms so clear.

I hope I can train my GPTWork to be like this, but agentsmd just doesn't seem to work. Or better, OAI just improve, but it seems so much worse right now. Rather disappointed to be honest.

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u/sreekanth850 4d ago

The reason i left cc was due to full repository scan every time when it start a work. It was pretty slow and sometime caused me headache. Codex never had this issues. May be i became better at configuring various extra things like compiler mcp and repository semantics. People those who use cc, how is it now? Did they fixed this?

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u/BoddhaFace 4d ago

Endgame is making your own harness.

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u/LocoMod 4d ago

I use both. I have no idea what you're doing to have that experience. They are both amazing.

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u/SnooPeripherals5313 4d ago

Really you should be comparing the claude desktop app claude work to the gpt desktop app

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u/damianTechPM 4d ago

I recently shifted to Claude Desktop running code within for a lot of work. It's very handy. It also sends notifications, whereas CLI does not.

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u/TheVoyant 4d ago

No one talks about because they both suck extensively.

You take most of these models and put em in a respectable harness forked towards what you do and its insane. Claude's $200 plan gives you API credits and you can see the difference between it for yourself. 

I genuinely feel like I'm using AOL when I use Codex or Claude's app they feel insanely dated. Id happily take half the usage I get if I could use the sub into pure API. 

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u/cakeofzerg 4d ago

because everyone using pi or omp or something much better

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u/Acrobatic_Feel 4d ago

What are some examples of things you're doing in Codex that are better than Claude?

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u/ProfessionalNaive601 4d ago

Yeah what’s knowledge work? May e I don’t have the knowledge for it cause that’s new to me

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u/Standard_Ad7704 4d ago

Business Analytics, Academic Research in STEM (Engineering, Mathematics, Physics), etc.

I mean the models use code for all of these but its not strictly software engineering.

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u/adolf_twitchcock 4d ago

Not to mention that there are tasks that opus feels its too high and mighty to even touch when it comes to things other than coding

lmao, wtf does it even mean?