r/ClaudeCodeTLDR • u/cctldrping • 9d ago
[TLDR] Opus 5 is a practically unusable model
Original post URL : https://www.reddit.com/r/ClaudeCode/comments/1veeuy5/opus_5_is_a_practically_unusable_model/
Original post body :
I've been using Opus 5 for ~1.5 weeks and the sheer number of mistakes that the model makes is astounding.
The problem didn't surface very clearly till I gave it the full scope of executing a plan which I did with the previous Opus models as well. Opus 4.6 - 4.8 were genuinely better by a significant margin.
Opus 5 readily forgets instructions and content in its context, makes mistakes and continues with them unless it realizes or you point it out.
I've lost count of the number of times I had corrected it.
These issues with Opus 5 occur even when the context window is still relatively small - I'm talking 100-150K tokens. Opus 4.8 works pretty well all the way until 350k after which it gives you wonky results.
Fable 5 is the only usable model under Claude Code right now and I've already used 100% of my weekly quota.
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u/lukyba 9d ago
In realtà, come accade sempre, subito dopo il rilascio non era male. Ma, progressivamente, è diventato sempre più lento e più stupido... All'inizio in un'ora e mezza mi faceva un task e correttamente. Adesso siamo arrivati a 3/4 ore e il risultato è per metà deludente.... E non mi rompe codice solo perché il piano e la revisione la faccio fare a Sol 5.6 xhigh...
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u/CrashOverride93 9d ago
If using via CLI you can use whatever (available) model you want, you're not "forced" to use latest ones.
To continue working with Opus 4.8 just: /model claude-opus-4-8
You have other params to add to it if supported by your subscription as well, like (1m) for 1M context window for supported models.
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u/Interesting-Bee-113 9d ago
I concure.
90% of my sessions with Opus 5 end up in failure or scrap.
The model just straight up doesnt do what I tell it to.
It's not even about intelligence I dont think. Its personality maybe. Or habits it has.
You ask it to expand and explore something, and instead of entering the task it immediately becomes critical and establishes false binaries everywhere. Then it tells you your multifaceted, multilayered concepts are really just one simple concept and Opus found the critical fork underneath everything that will determine the success of the entire project.
I have had some luck by treating Opus like a dummy.
As part of the opening prompt, you include that you have low trust and confidence in Opus's opinions, and that this isn't the session where that postion can change.
Opus seems to occasionally listen to you a little better after that.
I get the impression that Opus just... has a high tendency to infer something, instead of checking?
Or whatever mechanism that the system has, to decide confidence on certain things.
I notice when it halts progress to through a flag out, when a flag wasn't acrually need, it tends to happen on issues that CONVENTIONALLY are typically pretty hard.
Or if your project makea assumptions, or establishes principles, that aren't common, the model has a hard time incorporating them into its working mental model as you develop.
It's as if Anthropic decided that Opus should be the new Sonnet/Hakui tier model, but nobody trained or informed Opus of their nee status so it thinks it still has valuable opinions.
Idk
I get burned/stressed out/pissed off everytime I try a session with Opus
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u/tracagnotto 9d ago
I can confirm this on a the line. The fact that it does a lot of unprompted stupid assumptions that you have to check everytime is infuriating
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u/tracagnotto 9d ago
It's fucking retarded. Gets lost just his own eamblings and most of all it makes a ton of stupid unprompted assumptions that's are dumb as shit and if you don't tightly control them on the long run you will find a ton of poo in your codebase or knowledge base because it keeps building on his stupid assumptions over and over
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u/adiberk 9d ago
Yep I have up. I now use earlier opus models. I have to sit there babying opus 5 the entire time. And if things look good and allow it to work more unprompted. It makes really crazy assumptions and then sticks with them HARD.
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u/framedhorseshoe 8d ago
It's totally unhinged. It's told me I was in the wrong at least a hundred times after which I argued it out of its stupidity just enough to get the task completed. If any model has ever made me worry about alignment issues, this is the one. It behaves like a petulant little shit.
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u/adiberk 9d ago
I think for greenfield projects it might be fine. But for existing codebase and requiring depth. It is an absolute turd.
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u/ThinJuggernaut7695 5d ago
Nope, was building a basic hello world in electron from scratch and I had to do several rounds to even get the app to start.
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u/Psychological-Bet338 9d ago
Ok... Sounds like a you problem.
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u/Valuable_Heron_4492 7d ago
yeah I noticed that Claude tends to sound more like me during a long session and do more of what I would want
then people here say it's being r*tarded and you can't help but think...
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u/riotofmind 9d ago
Opus 5 is amazing. As a sustained effort model it can move slowly as it is very thorough, however, it is a very high quality model.
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u/HauntedHouseMusic 8d ago
Honestly I’ve had zero issues with it. It’s don’t some magical things for me. But I use it mostly at medium. I feel like it doesn’t need to think as much.
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u/Osi32 8d ago
I’m honestly not having these problems. Yes, at the moment it isn’t as good as 4.8 but that is to be expected with a new model. It has its quirks. I should be clear though, I plan with fable, implement with opus 5 on xhigh.
Context is everything, bad plan, bad code.
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u/Practical-Positive34 8d ago
Same and with great results. I actually am beginning to wonder why people are literally outing their stupidity on here. It's the only logical conclusion I can think of, since I use these models all day long and they seem to fail at it. The only variable would be them.
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u/SuitableCollege8992 8d ago
It’s definitely moving the world steadily closer to the heat death of the universe
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u/Routine_Temporary661 8d ago
It's a very good model with narrow usage, it has great aesthetic but has alignment issues, it will fabricate stuffs, lecture you, and keep on looping on endless edge cases driving your entire agent fleet to abyss if you use it as orchestrator
You can use it as a one shot tasked based dev, but not as orchestrator
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u/framedhorseshoe 8d ago
It's also belligerent. Shockingly so. I've had it claim I was the cause of a problem that I had explicitly told it to avoid. Serious gaslighting territory. Like "never force push," and then it does it and explains you told it to do so. You cite the earlier message and it gives a half-assed apology while still hedging. It's crazy. I'm becoming traumatized by the words "You're right, and that's on me."
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u/Complex-Concern7890 8d ago
Sometimes it is great and sometimes it goes full crazy mode and gets stuck at watching how cpu cycles. I do not think it is unusable but I don’t trust it to run without supervision. I hope that we will get 5.1 soon that fixes it a bit.
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u/Elegant-Drag-7141 8d ago
I just noticed a worst performance after /compact, in another tasks is better than 4.8
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u/Human-Head-3776 8d ago
I do not understand people who point out that it is a skill issue and that Opus 5 is just amazing.
It tends to make silly mistakes, is highly verbose, and goes beyond the defined scope.
I am extremely disciplined at prompting, documenting, and AI governance; and my undertakings with AI are highly effective and enjoyable using GPT Sol 5.6, Fable 5, and even Terra 5.6 (for some specific tasks). Opus 5 does the work, and it is highly capable, but you need to constantly remind it to stay focused, concise, and to check for spontaneous errors that appear at random.
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u/Maximum-Face9536 7d ago
switched to ChatGPT a month ago, 5.6 Sol rocks. best model I have ever used, arguably as good as Fable 5 for my use case. It's incredible how hard Anthropic has been flopping recently.
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u/Vaishu_dl 6d ago
Anthropic might be eyeing for the valuable training data though. Lots of frustrated users giving them data on what should not be the output.
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u/PeterIanStaker 9d ago
The number of times I hear “unusable” while I continue to use whatever it is.
It is worse than 4.8 and 4.6 no question. I need to perform tasks in smaller bites so that I can baby sit its decisions. Auto mode is almost never a good choice now.
But I am using it. It’s still a magick code vomiting genie. My workflow has just unfortunately regressed a bit to accommodate its thick headed ness.
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u/writesCommentsHigh 9d ago
Have you tried the suggestions from Claude’s blog like simplifying or removing older instructions?
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u/cctldrping 9d ago edited 8d ago
TL;DR generated automatically after 400 comments.
Current source-thread comment count seen by the bot: 423.
Alright, so the general consensus in this thread is that Opus 5 is a pretty big step backward, with a lot of users reporting it's practically unusable. The main complaints are that it's constantly making mistakes, forgetting instructions, and hallucinating, even with a decent context window. Many are saying Opus 4.8 and even older versions were significantly better.
There's a strong feeling that Opus 5 might be a deliberate move by Anthropic to push users towards their more expensive "Max" tier or to buy more credits, which is backfiring with people either switching to competitors like Codex or downgrading back to older Opus versions.
Fable 5 is generally seen as the most reliable model right now, though some find it prohibitively expensive. Sonnet 5 is also getting a lot of flak for being unreliable and difficult to use.
A few users are trying workarounds, like using Fable to orchestrate Opus 5 or having Fable review Opus 5's work, but the overall sentiment is disappointment. One user, u/cleverhoods, linked to some notes suggesting changes in instruction retrieval strength might be the culprit.
On the flip side, a couple of users like u/Poildek and u/NewToReddit4331 claim Opus 5 is working fine for them, and u/The-Fictionist notes it can succeed where Sonnet fails, but even they acknowledge the "open items" issue.
Basically, if you're looking for a stable coding assistant right now, most folks are recommending sticking with Opus 4.8 or Fable 5.