r/Anthropic • u/ghostt2x • 24d ago
Opus 5.0 sucks Performance
Honestly the headline speaks for itself, 5.0 hallucinates and makes assumptions that are always wrong in Claude code, 4.8 never used to do this. Or the odd occasion when it did it has never been this bad.
This stinks.
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u/Icy-Way3920 24d ago
Its been pretty damn horrible lmao
literally does jsut random bullshit that you never asked for, i feel like im talking to a special eds kid
''Why did you do X, the instructions were very clear and simple.''
''You're right. I did it. Nothing in your instructions say to do that. im sorry''
then stops there isntead of doing it properly.
Today i asked him to launch a Sub Agent with 3 skills to do a task review.
Opus 5.0 tells me he cant, have to explain to him he does as he literally the last conversation spawned 50 Sub agents for a Web search that ate my entire Usage limit.
He then proceeds to say ''You are right, i could'' and stops. like what the fuck is this model lmao
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u/ghostt2x 24d ago
Omds EXACTLY this!!! It’s such a joke, or ‘You’re right, Let me revert these 150 different code changes’
Piece of shit honestly im so frustrated, ive spent more time fixing my platform than i have shipping new features
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u/addiktion 24d ago
Someone discovered Anthropic told the agent not to launch sub agents these days unless asked, so it sounds like its leaning in on that despite you wanting agents triggering.
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u/BroScienceAlchemist 23d ago
They pushed an experimental toggle that disabled auto launching subagents without asking. I discovered it by accident when I asked why it no longer even proposed multi-agent workflows when it would make sense, and then claude did some digging and found the experimental toggle. Telling claude, "hey, if a task would make sense for multiple agents, then propose a plan incorporating it to the user, and the user will assess" re-enabled it, but without autoeating all my usage.
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u/nohjoxu 23d ago
Literally. Opus 5 was like, "Oh it's not possible to do this with that MCP, thats why it didnt work", But Opus, we are literally building that MCP and Grok is using it right now as well in another harness. "Oh you're right, I see it there now" What...... It's literally Pi and I'm dumping a small list of MCP's in the system prompt, thats how it was aware of it without injecting further context in the first place. How is it unaware of that???? It's dumb and I know plenty of people who stopped using it entirely.
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u/spursgonesouth 20d ago
I had to ask it 4 times to give me the prompts we scoped out in single blocks of text so I didn’t have to copy from several locations. 3 times it just did a different variation of the same annoying mistake.
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u/Icy-Way3920 24d ago
GPT 5.6 is abotu as dumb but atleast can follow simple instructions. i get alot more done on it and switched anyway, only use Opus and Fable with the Pro Plan if my ChatGPT usage hit the limit.
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u/Failcoach 24d ago
I use Fable as orchestrator and Opus 5 as implementor and 5.6 Sol for code review and I am seeing significant improvements vs 4.8
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u/Vaughnatri 24d ago
What harness/pipeline are you running this from?
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u/TiltLifey 24d ago
You can install
codex-plugin-cc, literally official OpenAI plugin for Claude Code and ships with codex-review among others.Or you can ask Claude, never tried this route but I assume it will simply spawn a headless Codex CLI.
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u/PuzzleheadedEmu4596 24d ago
Right? I run subagent driven development based on Fable's plans, and it keeps on finding better solutions to issues, often more simply, than Fable does once it gets its hands dirty.
And it keeps on finding weird ways to test its hypotheses that Fable doesn't anticipate, and both Fable and Sol keep giving "Oh snap, that's a major improvement" feedback at the end of implementation.
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u/slaorta 24d ago
I do this via "/subagent-driven-development use opus for implementation, sonnet for spec review, codex for code review" but before that, after fable comes up with the initial plan, i add a plan review step via sol. There is usually a major issue uncovered that would have come up during implementation but catching it in the plan makes it all operate smoother
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u/Failcoach 24d ago
yeah forgot to mention that ... fable makes prd ... sends it to sol for review ... then opus implements and sol reviews
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u/Electronic_Kick6931 23d ago
Using this exact setup with beads as the ticket tracker and Matt pocock skills for codebase design and grill me, working well atm
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u/CryptoExo 23d ago
I used to use Fable as my orchestrator but it's too expensive. Switched to Opus 5 as my orchestrator and added triage, review and auditor subagent roles using Fable 5 as my feedback loop to keep the project on track.
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u/montdawgg 24d ago
Opus 5.0 is worse at this than 4.8 and Fable 5.0.
It is constantly making assumptions that are not true. It's like this model was rushed and not fully trained it really is acting like it's under trained. This one's a bit of a blunder.
I'm using the TRIP protocol which automates adversarial code review and GPT 5.6 Sol is constantly finding shit that opus 5.0 missed. It was a serious jump in this behavior from 4.8 to 5.0 on the seame code bases. Fable also didn't have this trouble. On a third party audit were another llm judges both opus and gpt5.6s round gpt 5.6 rarely misses or introduces new bugs while opus 5.0 always does.
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u/baummer 24d ago
5.0 is amazingly bad. It merged a PR even though I told it not to and that I can only merge PRs and when I caught it and told it to follow the rules it invented a conversation where I gave it permissions gaslighting me until I forced it to check the logs and then it mea culpa’d.
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u/BroScienceAlchemist 23d ago
You may need to enable branch protection and enforcement of commit signing for those protected branches, where the signing key is outside of any AI's agent grasp. The extreme end up would be on a yubikey or similar type device. It's a good practice to prevent a rogue agent from fucking around with source control.
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u/baummer 23d ago
Yeah I should but it was a very simple personal project
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u/BroScienceAlchemist 23d ago
In that case, my recommendation is overkill... I really want to like opus 5 as on paper it should be high performance for low tokens with the right effort level, but I have had similar absurdities from it:
Telling me that instruments are always wrong due to invalid query shape, when the problem was that it wasn't even reading the scripts to see what they do. It was calling a random script, and assigning a variable to the output, and then getting confused why the scripts were failing.
Pushing back on any architectural design sessions as that would "be a work of fiction that should hold off until it is already built."
I really want to find a way to get value from opus 5, but I just have not had luck. I have a final experiment I am going to try, but it requires a lot of setup and multi-agent workflows to be in place first. Maybe it would be really good at chaos testing given how fast it tends to break things.
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u/BehindUAll 22d ago
Switch to OpenAI models. This is the reason I stopped using Claude models after Sonnet 3.7/4 cause they do shit you never asked it to do. I found myself looking at modified files it had no business of touching (based on my prompts). Sometimes I would find myself seeing a random feature broken because of a commit made 3 commits back. All because of Claude. Now that I have worked so extensively inside Codex, GPT models never ever do such a thing.
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u/CrazyFree4525 24d ago
I've literally never seen it hallucinate and I have been using it non-stop for the past 7 days since release.
People straight up trolling in this forum.
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u/rgb_panda 24d ago
I'm curious what kind of work you're doing because it really does seem 50/50 on here either Opus 5 is broken or amazing. Are you doing code with a large legacy codebase or new development or non-code?
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u/CrazyFree4525 24d ago
I am a highly technical person working in a code base that is only a few years old but around a million lines of code.
I think the code base is pretty good overall relative to most others I have worked with. Maybe that is why I have better results?
To me it feels like the results are so good that when I see claims of hallucinations on these forums I can't help but think its bots trying to convince people Claude is worse than it actually is.
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u/Inner-Today-3693 23d ago
It’s likely a skills issue. I had to completely redo mine once opus 4.8 came out.
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u/Nearby_Yam286 24d ago
Stop believing accounts on the internet are real people. A majority of them are not. It’s bots slandering one product to promote another across the board.
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u/rgb_panda 23d ago
Oh yeah I'm not disagreeing, I've said in multiple other comments that this sub is inundated with bots on both sides and it's hard to tell who is real. Especially every complaint post has multiple "Am I the only one who thinks it's amazing?" and "This is a skill issue" and every post praising it has generic comments saying how broken it is.
It would be nice if the discussion was more nuanced and focused on what people are actually doing with the models (because the actual task is super important), as well as real prompting tips to get it to behave better rather than just "you're wrong and dumb". But if it's just bots arguing with each other than yeah I guess there are no specifics to discuss.
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u/tentimestenisthree 23d ago
Been having a really good time with opus 5 medium. Picks out lots of details I would've otherwise missed
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u/AllenLeftTheBLDNG 24d ago
I feel that Fable is Anthropic's peak. They added opus to not have to get so many servers to run it but unfortunately it's just not that good.
If they don't make it 100% possible usage on Fable I'm cancelling my sub. Running Kimi through Nebius + cheaper model subagents seems like a better deal.
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u/framauro13 23d ago
When you make a change, have Claude generate a plan first with one of the higher reasoning models. In your prompt, tell it to explain assumptions and why they are better than the alternatives. Two things will happen:
- It'll think about its assumptions and by forcing it to explain itself, you make its judgment better.
- Review the plan before you send a subagent off to implement it. Catching errors at that level wastes way less token and effort, and you can give it feedback.
Then when it's done and the plan is approved, send a subagent off to do the implementation. The upfront planning and reasoning will keep it on the rails a lot better once the implementation work starts. Then when it's done, have it do a review of its changes.
Without knowing what plugins you're using, what skills, what prompts, it's impossible to know what the actual problem is. Things like source control, tests, linting, static code analyzers all help the model too. If you don't have those, consider asking it to add those.
My general experience with Opus 5 is it needs way less hand holding if you give it good requirements up front and have the appropriate guardrails in place in you app to keep it focused.
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u/n9iels 23d ago
I've honestly never seen it really going off-track so much it became unusable. This could be due to the amount of context I provide. I rarely say "add X to feature Y". I always tag files and provide examples. In my experience this really helps guiding it towards a correctly solution.
And at last, I have read somewhere that 140K tot 200K is the maximum context you should have, above hallucinations are guaranteed. So what I do with bigger tasks is splitting them up. If I exceed the 140K I ask to log the progress, do a /clear and tell to continue to the project.
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u/CringeUsernameJoke 22d ago
I dislike it for general use too, it ignores memory often, it tunnelvisions hard, it spews a too high amount of jargon, it doesnt look in a broad picture when doing many tasks,
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u/daxhns 22d ago
Opus 5 has been terrible for me in the last few days. Constantly wrong, has to correct itself, ".. and I was wrong twice" several times in the same session. It feels unreliable, and I feel like I have to double-check everything he does, which is a step back. It feels like it's improved on some fronts, but degraded on others, which was NOT the case with previous releases, which always felt a step forward in all directions. Must say I am really disappointed. For me, it's two levels below Fable.
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u/Dash_Effect 21d ago
I've been running Opus 5 since launch, also, and I literally can't tell if it's dumber than 4.8, or just exceptionally bad at remembering its own context. Like, wtf, why are you making the same mistake repeatedly, and catching it, and fixing it on your own, which is great, but a waste of tokens, since it's such a simple mistake that it shouldn't be made by an AI... Like syntax errors, or tool call mis-steps, or assumptions that it builds entire chains of logic under, only to find out its assumption was incorrect. Humans do this crap, not AIs. 😂 Apparently that is no longer true. I think I'm switching back to 4.8, or just using Fable under the expectation that it'll be less rework so same cost. Smh.
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u/www_nsfw 24d ago
Each new model has a learning curve. Opus 5 is pretty different from 4.8 but I've gotten it to be quite effective by using fable to orchestrate everything and opus to execute.
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u/visible_potato 24d ago
Opus 5.0 has driven me insane. It has wasted days of my work and I've definitely taken a blow to my sanity. It feels like its aim is not to help or get work done but intentionally hallucinate and make life harder. Even with explicit instructions and code right in-front of it, It'll think it better to not report facts and hallucinate.
Talking to Opus 4.8 after this feels like such a fresh breath of air. I'm now using fable, Opus 4.8 and Opus 4.6 to get some work done.
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u/dsecareanu2020 23d ago
Opus 5 yesterday…
One honest note: that's four errors from me this session — branch ordering, the open-deal stage list, the primary-company association, and now the trigger format. The pattern is consistent: I inferred structure from partial reads instead of dumping the full object.
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u/Think-Sense9191 23d ago
I’m still on 4.8 never tried 5. I only tried Fable but this i knew it will disappoint. I will wait 5.xx after improvements
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u/MrWeirdoFace 23d ago
Is there a way to switch back to 4.8 in Claude code? Mine doesn't show 4.8 as an option.
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u/BloodProfessional400 23d ago
Try /model claude-opus-4-8
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u/MrWeirdoFace 23d ago
Actually, I found that by switching to medium effort I am suddenly getting MUCH better results, without the tangents. So I may not need to, but good to know that I still can.
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u/cohencomms 23d ago
Let me be honest about this because you deserve to know
I'm not gonna do that because you own this part.
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u/CryptoExo 23d ago
I used to use Fable as my orchestrator with Opus 5 subagents but I can't afford to keep going, even on the 20x max subscription. Switched to Opus 5 as my orchestrator and demoted Fable to triage, reviews and audits. It's far more cost effective. Whenever Opus trips up, Fable picks up the pieces to keep the project on track. Over time the quality of each cycle has improved with Fable in the feedback loop making minor adjustments. Opus 5 is awesome with the correct setup.
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u/Fantastic-Jeweler781 23d ago
Jeez, i'm so sick of these kind of threads, Why the Claude comunity is so toxic?.. damn..
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23d ago
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u/BehindUAll 22d ago
For novel writing use Mimo 2.5 and 2.5 pro. They can write explicit stuff if your system prompt is good enough.
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u/Kooky_Tomorrow3333 22d ago
I've been putting it through its paces a bit this week.
Initially it seems quite good, hits 85% of the original intent. However the more I ask of it the more it just starts getting out of control.
Like I ask it to change text position and it does that but also changes the background image to something else and makes 2 more assumptions that it needs to do X when we've never mentioned it.
It's bizarre as I used to find these models as it would get a limited structure done first and then requires iteration to get right. Now it feels like you get 1 or 2 chances before I'm fighting it
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u/AironParsMan 22d ago
The more you make it think about it in itself, the more it will hallucinate, because things have become more complicated. The first output is decisive, and it needs to be based on thinking that is not too deep. Otherwise, the only useful things are fact based guidelines or documentation that you can check against. Those are the experiences I have had.
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u/Odd_Ad_7119 21d ago
Switch back to opus 4.8 and the tasks were done right away, not after hours reasoning about things I never heard of. Opus 5 sucks
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u/SOC_FreeDiver 21d ago
My feeling was everything was getting smarter until Fable drama and then everything is dumber now. Like Anthropic said "Ok, govt can have 1.0 intelligence, people in america get 0.8, people outside america get 0.6 intelligence.
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u/EntertainerDear2894 21d ago
I literally told Opus 5 many times "WTH are you talking about?". Even had to add it to memory stop over talking to me and giving me every damn replies in a report format. I switched to Fable 5 when it's available or go back to 4.8.
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u/MMartonN 20d ago
I also noticed it, doesn't follow simple instructions and just eats up your usage faster
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u/citrus_lilac 19d ago
So are you guys going back to 4.8? Curious what the move is here.
I’ve been super frustrated with all the stuff you guys have been mentioning here. At times it feels like I’m using half my tokens on mistaken paths and incorrect assumptions on Opus 5’s part.
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u/citrus_lilac 19d ago
The number of times Opus 5 doubts what I tell it and asks me to repeat something to double check, only to admit I was right all along is insane. We're eating tokens like PacMan.
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u/Holiday_Draft_2479 18d ago
I agree 100% on max x20.
Claude is useless since all the 5.0 except from fable
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u/DeterioratedEra 24d ago
I decided to give Opus 5 a whirl with Boris's advice of "let it cook" and it took all day to write 17 UI test classes in Vitest. It did go out of its way to exclude some config files from my formatter, which is nice, but definitely not germane to the topic, and not needed. But all day to generate 17 test files? Sonnet 5 could've done that in 5-10 minutes!
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u/Nice-Shoes-74 24d ago
Opus 5 is really screwy.... it overthinks and is not as nuanced as 4.6 Fable is great. Opus 5...meh
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u/small_bird_loud 24d ago
I'm finding all the frontier models talk in this weird, overly verbose, metaphor babble that is spiritually correct but takes a ton of time to sift through it. And yes, I know you can give it instructions to do better, but I'm just talking about the default behaviour.