[magicalhippo]

In addition, the harness around these models do a lot of work and changes the outcome significantly.

I just had an issue where Claude CLI with Opus 4.7 High could not figure out why my Blazor Server program was inert, buttons didn't do anything etc. After several rounds, I opened the web console and found that it failed to load blazor.js due to 404 on that file. I copied the error message to Claude CLI and after another several unproductive rounds I gave up.

I then moved the Codex, with ChatGTP 5.5 High. I gave it the code base, problem description and error codes. Unlike Claude CLI it spun up the project and used wget/curl to probe for blazor.js, and found indeed it was not served. It then did a lot more probing and some web searches and after a while found my project file was missing a setting. It added that and then probed to verify it worked.

So Codex fixed it in about 20 minutes without me laying hands on it (other than approve some program executions).

However, I'm not convinced this shows GPT 5.5 being that much better than Opus 4.7. It could very well be the harness around it, the system prompts used in the harness and tools available.

For reference this was me just trying to see how good the vibecoding experience is now, so was trying to do this as much hands-off as possible.

[manny_rat]

I’ve run into this exact situation several times recently. They were all tasks that I’m positive Claude Code could have managed in the past, but now it simply cannot get over the finish line a lot of the time, and Codex will one shot fix it just like the old Claude Code could. I’ve even tried having Code fix and implement some old tasks it had done correctly in the past and now it simply can’t.

My guess is that it is the fault of the model rather than the harness, I believe Opus to be much worse than it was for whatever reasons. Though I suppose it could be Code’s fault somehow. For the time being though Codex is much better which I never thought I’d be saying.

I plan to run tests using Pi so they have the same system prompt and harness, but I’m suspicious that it’s only the subscription level Claude Code that is worse and we’re not allowed to use that with Pi.

[59nadir]

> However, I'm not convinced this shows GPT 5.5 being that much better than Opus 4.7. It could very well be the harness around it, the system prompts used in the harness and tools available.

A model that can more effectively make use of the tools presented to it is going to be better. You're not wrong about the system prompt; these can have quite a pronounced effect, especially when what the agent is bridging to is not just a case of bash + read/write; you need the prompt (and tool descriptions) to steer and reinforce what it should actually do because most models are heavily over-trained on executing bash lines.

When it comes to more basic agent usage that just runs in a terminal and executes bash ultimately most models are going to do just fine as long as you provide the very basics.

Regarding your case in this post it could be any number of issues: The provider being over-provisioned, leaving less time for your case, the model just not being particularly great, your previous context (in your original session) subtly nudging the model to not do the correct thing, and so on.

The truth is that you simply can't really know what the exact cause of this behavior you experienced is, but I think you're also working hard to cope on behalf of Anthropic.

All in all I think you're placing a bit too much faith in agents and their effect. If you slim down and use something like Pi instead you'll likely get a more accurate sense of what agents do and don't do, and how it affects things. You can then also add your own things and experiment with how that impacts things as well.

I've written an agent that only allows models to send commands to Kakoune (a niche text editor that I use) and can say that building an agent that just executes bash + read/write in 2026 is probably the easiest proposition ever. I say this because a lot of the work I've had to do has been to point them in the direction of not constantly trying to write bash lines; models all seem to tend towards this so if you just wanted to do that anyway most of your work is already done. The vast amount of the work in those types of agents is better spent fixing model quirks and bad provider behavior in terms of input/output.

[magicalhippo]

> A model that can more effectively make use of the tools presented to it is going to be better.

Of course. What I was getting at is that if the harness A doesn't expose certain useful tools that harness B does, it doesn't matter if the model could use those tools.

> I think you're also working hard to cope on behalf of Anthropic

How on earth did you get that out my post? I was just reporting on a recent experience I had, to make a point that harness+model is a very different thing from just model when it comes to evaluating effectiveness and quality of output.

[Chyzwar]

You can fix Claude's laziness by modifying the system prompt. https://gist.github.com/chyzwar/99fe217c3ed336f57c74dcffe371...

[veber-alex]

I actually noticed this too. GPT 5.5 is much more "hands on" with calling tools to debug issues and verify results. I did all my tests in Cursor but I don't know if they use a different system prompt for each model.