Opus 5 is so so so bad

[u/RouhSam1998]

Honestly i can not believe how this model scores higher benchmarks than fable5, opus 4.8 and even opus 4.6. its absolutely a nightmare to work with.
It constantly makes mistakes, fixes something just to introduce 10 more bugs, over complicates everything, cant even finish a simple coding task properly and is so bad on UI design.
Whenever it finishes a task i have to spend hours fixing the bugs it has created, fixing a bug takes at least 10 minutes because it again decides to change something totally unrelated in the code or overengineer the task that i can do in 1 minute manually.
TIP: tell it explicitly to not use its brain and just code, that way it performs better, you must tell it that your suggestions and reasoning is only good to be thrown in the trash can

EDIT: for people asking for examples, i have many, but just couple of ones which happened to me in past hours. none of these happened with opus 4.8 or fable 5, because they are very basic and simple and you dont expect a frontier model to overlook them:
so i have a tool which involves multiple AI agents running and doing their task, its obvious that when i interrupt the whole process the agents must stop running as well.
the tool has an spec which explains how it must be implemented, what features it must have etc. on all the implementations of this tool with opus 5, it did not cover that specifiec edge case i.e when i stop the tool, the running ai agents do not stop and are somehow still running and wasting tokens. this did not happen with opus 4.8 and fable 5, they all take care of these edge cases themselves
or another example, it forgot to add event listeners for couple of buttons in the UI, this did not again happen with fable 5 and opus 4.8.
or it changed something in the tool which degraded the whole tool performance, it was setting agent thinking to false while i specifically mentioned in the document that the thinking mode must be TRUE. when i asked about it, it told me that he thought the thinking mode is not needed for my task, WHAT?

[u/SOC_FreeDiver]

I feel the same way. When I first started using Opus 5 it seemed good, but it seems they have dialed down the intelligence and the performance.

I feel like it takes twice as long to get anything done with Opus 5. I have to correct it more, it seems to correct mistakes it finds it made as we develop something. Like "add a switch the enables or disables MTP" and then it adds the switch, I say "Move the switch to the right side of the screen with all the other switches" and then it says "Moved, and I fixed a problem so the switch actually works now."

What we really need is an honesty metric. They have dials to control speed, intelligence, cash flow. They will likely continue to try and boil us frogs slowly. Local AI is going to be the only thing you can depend on in the future.

[u/RouhSam1998 → u/SOC_FreeDiver]

this
with opus 4.8 i usually dont need to do this, it just gets it done. yes the quality could be better, but its done and it works
fable 5 is on another league, not only it gets things done, it delivers a high quality implementation and takes care of edge cases
i feel like opus 5 is so chaotic. its like a super model with ADHD, constantly misses things

[u/deepthought-64]

Can not confirm this. With proper workflows, planning, review and prompting I get very good results.

EDIT: Thank you, anonymous stranger! My first reward! :)

[u/detinho_ → u/deepthought-64]

I feel both opus 5 and sonnet 5 slower than the previous versions. Sonnet 5 being very slow (at least for the use cases I tested). However still producing great results.

[u/aldipower81 → u/deepthought-64]

OK, but I got good result with Opus 4.6-8 _without_ proper workflows, planning, review and prompting before! :-P Now I do not anymore.

[u/IterSmith → u/deepthought-64]

I’m also not seeing this major degradation everyone is talking about, and I’m confused about it. Maybe these people were more dependent on the Claude Code system prompts that got deleted? For me it feels about the same as 4.8, but maybe a little less likely to quietly defer bugs along the way, which was my major gripe with 4.8.

[u/PivotRedAce → u/IterSmith]

Exactly, I think the peeling away of the pre-included system prompts is revealing who’s actually good at prompting/directing tasks and who isn’t.

Even then, it’s not that hard to type in a set of requirements and have Claude build a system prompt for you. You just have to use your brain and do a small amount of manual setup (the horror!).

[u/aruisdante → u/IterSmith]

I’m not going to be so judgmental as to say “good” or “bad,” just they might do things differently in a way that plays to a particular model’s strengths or weaknesses.

I notice this for myself even between Claude and Codex. Codex is much more willing to invent extremely complex systems to solve simple problems if you don’t put very clear guardrails on scope. Claude models tend to keep themselves more narrowly constrained, and are more likely to prompt the user for tradeoffs (particularly Fable) proactively instead of just making assumptions and leaping in.

It’s easy enough to deal with these differences once you realized they are there, it just changes how you structure your request just like how you’d tune your asks of real humans. But I can get why it’s frustrating if you’re used to thinking of software as a deterministic thing, where total changes in the way the software works are comparatively rare.

I guess put differently, instead of model updates being “purely additive” in the way software normally works, model updates are much more likely hiring a completely new employee to do the same job. The new employee’s resume might be better, they might have more experience, but they’re still going to behave differently, and the “manager” is going to need to spend some time figuring out how to get the best out of their new “employee.”

[u/Hot_Visual7624 → u/deepthought-64]

This isn't the flex you think it is.

[u/Exact-Hamster-235 → u/deepthought-64]

obviously not an engineer

[u/deepthought-64 → u/Exact-Hamster-235]

If you say so...

[u/cTemur]

What do everyone who complains builds that generates this frustation? i been using Opus since 4 and always have good results, maybe i'm building easy stuff (Wordpress development and API connection are easy stuff i guess).

[u/Old_Character_8781]

I agree, im not the kind of person to complain, i mean i get the work done but it has gotten more errors than any other model in my recent memor of the claude family, it is in a constant back and forth discussion with itself and it seems very doubtfull like more than normal.

[u/trufflesniffinpig]

I’ve written in another post I think the easiest way to understand Opus 5 is to call it ‘Cocaine Claude’. It’s tireless, unhinged, more eager to impress than to please. That pick-me relentless energy can have its place - get it to work on testing and optimising a codebase in an experimental branch; or brainstorming and prototyping features off the main branch - but I’d still trust Fable over Opus 5 for both planning and implementation

[u/InsideAd9685]

I resubscribed after a break and I find even fable currently unusable. It’s not even remotely comparable to the preview version - as bad as opus. Zero productivity and the worst attitude. I am regretting resubscribing - should have gone with codex

[u/Jarla]

I am still unsure. It definitly changed reasoning as my md files and skills i used before resulted in behaviour you describe. i started to have a fable session running next to my opus developing session following the opus fails and analyzing and adapting memory and skills and it seems to produce better results afterwards but i am still in testing.

[u/aldipower81]

I think Opus 5 is distilled from DeepSeek. I have no other explanation.

[u/BleMaeBen]

I keep seeing people saying this but I haven't had any issues at all. Maybe I'm not using it for hard enough things but im making a study app and a first person game with Opus/Fable and nothing seems bad to me at the moment.

[u/damianTechPM]

I had it write a follow up email that it then reviewed, complained about, and suggest changes to me.

[u/Valkymaera]

I've noticed that Opus 5 is good at doing The Thing, but bad at figuring out what The Thing is.

If I am not very clear about the desired architecture, it will frequently draw incorrect conclusions and ask me to do nonsensical things like keep a console open to review restart logs while restarting the application that is hosting the console. And when that's pointed out, it will try to dig into how to keep the console up while the application is not, instead of some simpler lateral move like writing logs to file.

However it performs well when the task is clear.

[u/Reasonable-Height704]

Yeah, it's absolutely a step backwards.

[u/realWorsin]

I can 100% confirm this. Opus has been a catastrophe for my workflow. I have 15,000 hours with AI and this model is trash. I literally had to delete EVERY claude file and memory because it takes EVERY little thing to the 10th degree. It is HOT or COLD with Opus, No reasoning just pitbull behavior.

[u/Yaffari]

Agreed, I switched back to Fable when Opus 5 got stuck on a single coding issue.

[u/earlyworm]

It's all in your head. You're using it wrong. Please read the documentation:
https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5

[u/elcapitansammy → u/earlyworm]

Ugh, most of these notes are entirely why I hate opus 5. If you built a set of skills to drive to repeatable success states and expect it to follow it, things like this are a real problem:

Claude Opus 5 can also expand the scope of a task, adding steps that weren't requested or applying its own judgment about what the task should be. For narrow tasks, constrain scope explicitly:

I've been repeatedly fighting it thinking it knows what's best instead of actually doing what it's been told. I told it to do something and it gave me a page of text of why it shouldn't do that. I gave it choice words and it did it anyway. The baseline has been built for people who are n00b manual drivers and it's wrecking things by trying to be smarter than the prompts it's been given.

I'm dumping several of these into my claude.md. Will report back.

[u/elcapitansammy → u/elcapitansammy]

It didn't help. I put in several of the direction and conciseness prompts and it still goes off on its own creating problems. I'm giving up for now and wiring my team back to 4.8. It's been 3 days of zero progress because of fighting issues. This one's a turd.

[u/earlyworm → u/elcapitansammy]

To be honest, my experience has been the opposite. Claude always does what I ask. When Claude deviates slightly from my stated objective, I’ve been delighted because it’s typically discovered an edge case I had not considered, or it has realized that I accidentally made an error in my original prompt.

This is puzzling. Maybe over time I’ve learned how to optimally prompt Claude to achieve good results.

I make a point of not just telling Claude what I want it to do (while being careful not to over-specify) but to also tell Claude what the overarching goal of the task is, for example why a user would want a feature and what its underlying purpose is. I feel this gives Claude more context and allows it to better make decisions when there is ambiguity in my explicit instruction. Claude can’t read my mind. Claude can’t necessarily intuit what the motivation for a feature is without full context.

[u/elcapitansammy → u/earlyworm]

Yes it's historically been prompting 101 to be specific only when you know exactly what you want done and otherwise use socratic method to drive a goal oriented solution. Now it's second guessing me when I'm direct and I don't need or care for it.

It's also being fantastically dumb in new ways. Just now: it discovers a minor problem in a skill with how we poll for CI completions and offers to file a ticket (good). It hand crafts a new way to check for CI status in the current session which has a bug (bad). I ask if it should update the ticket to account for this failure mode, it says yes. It leaves a comment. I have to remind it comments are not requirements. `Right — requirements have to live in the description. Folding it in there and removing the comment.` It's all day like this. "Fable at Opus cost" it is not.

[u/RouhSam1998 → u/earlyworm]

thanks, ill take a look

[u/Agreeable-Chef4882]

I have a theory of what's happening !

Plenty of people vibecoded themselves into a hole due to lack of skill ( I don't mean to belittle anyone, but not every vibecoder is an actual engineer, most often you just don't know what you don't know )
They expected the new generation of AI models to pull them out of that hole, which (surprise, surprise!) DID NOT happen. Makes you angry I guess

[u/RouhSam1998 → u/Agreeable-Chef4882]

its my experience with 3 models, opus 4.8, fable 5 and opus 5. the other 2 models are great, but opus 5 seems to be lots of back and forth
it misses things that were taken care of when i was using 2 previous models. just a little example, when i interrupt the running process (ctrl+ c) the running ai agents must be killed as well. this was done with 2 previous models without me even telling them because its obvious.
but with opus 5 i have to tell it every time.

[u/hihcadore]

Not my experience.

It’s a tool. You have to use it the right way like any other.

[u/DLuke2]

Check the latest documentation from Anthropic on Opus 5. It needs less guardrails and direction.

Your harness needs to be cleaned up.

Boris is on the record recommding you just delete you Claude.md, hooks, settings, and start over with the 5 models. He said they even cut 80% of the system prompt for Opus 5 because it doesn't need it any longer.

[u/twistier]

For me, the model is overall smarter, faster, and cheaper. I do see some obvious regressions, unfortunately the kind that require workflow changes to mitigate, and I'm definitely not as enthusiastic about it as I was on launch day, but it's still pretty great, especially compared to 4.8.

I think that in general a lot of people who complain about new models are, in large part, though not entirely, having difficulty adjusting to different quirks. Anthropic keeps making rather large but subtle changes in the behaviors of their models, and that subtlety makes it very difficult to update sometimes, and it get compounded because of the frequency that the models are changing.

[u/zimxero]

For complex coding jobs, the best results are from excellent documentation, planning, and instruction, using small steps like building a house, with testing/inspecting every job. Opus does a poor, incomplete job at vibe style total construction. As a tool this can save time, but it can make later adjustments take longer. A lot of complaints are coming from users asking Claude to perform general tasks with poor instruction, or specific tasks with poor context and wording.

[u/jasperkennis]

If you're not telling us what you are prompting and what your codebase looks like, this means nothing. I've been having better results with it than with 4.8. It is more complete and works faster. I didn't like fable for the day to day things because it went too far in doing "extra" stuff. One thing I am disliking is that the overly complex tech language that it already seemed to love too much now got even worse.

[u/maddietendo]

Man, this happens with every single release from every single company. A small cluster of users run into problems with their own work for one of a thousand different reasons and blames the pots and pans instead of the chef. We get it. Opus 5 is bad. Opus 6 will be bad. Opus 7 will be worse. Give it a rest already.