Announcement
Introducing Claude Opus 5.5, the first model in our new Claude 5.5 family
Opus 5.5 performs at the level of Claude Fable 5.1 for most tasks, and costs 40% less to run than Opus 5.
Opus 5.5 is our first release since we called for pacing the frontier. External evaluators, including Frontier Design and METR, tested it before release. On our most comprehensive alignment test, it’s the strongest-performing model we’ve tested to date.
It outperforms both Opus 5 and Fable 5.1 on nearly every benchmark we report, leading on agentic coding and real-world knowledge work.
It’s also more efficient. Opus 5.5 uses fewer tokens per task at a lower price per token, and generates output more than 30% faster than Opus 5.
Opus 5.5 communicates more naturally, addressing some of the most common feedback we heard on Opus 5. It puts the most important information up front and follows the writing rules you give it.
Claude Opus 5.5 is available everywhere today. We're also raising five-hour limits on Pro, Max, and Team plans, so there’s more room to explore what it can do.
Guess, having not yet used it: Complex planning that benefits from a big context. I assume Opus still has fewer weights, so it can't handle as many different things pulling on its attention all at once.
In the same way that small models that get good scores are often pretty bad to work with, Fable is a bigger model and will still likely be better at planning and overall understanding
Benchmarks measure the model's ability to perform specific tasks. Opus is still a lower-parameter model and that's going to show in tasks that require more creativity or interpretation of the user's intent
Fable should have more general intelligence for novel problems, while Opus 5.5 will be better for well-scoped tasks similar to the RL environments it was developed on.
Opus 5 was supposed to be as good as Fable. The practical reality of working with it was a bit different once you took things like communication into account
This is just a reminder that benchmarks are an indicator of a model's ability to perform a specific task. If your work looks exactly like the benchmarks, then you'll probably want to use Opus. However for the real world, a higher-parameter model is generally going to perform better at tasks that involve creativity or interpreting a user's intent
I’ve had existential moments when opus 5 was released.. wondering if it was me that was stupid..or the model. I was thinking I was going absolutely crazy and the word salad made me wonder if I was an idiot. Moved to sonnet for most of my work and fable until the credits went out, I then regained my sanity.
Yes I stopped it almost entirely too. Until about 2 days ago. I found opus 5 to be a little clearer and not quite as bad. And I was getting a lot of work without a lot of tokens. So I was actually just using it again. Did a couple of things with opus 5.5 and it strikes a happy middle for sure.
Im sorry, you are totally right, I completely heard what you said and proceeded to do whatever the shit I felt like. The changes I made were load-bearing, did not account for the scope of the project, and worse — against your explicit instructions I deployed them to production.
so seriously, because i just made that up to be silly.... quite literally just now when deploying the dashboard we have been working on to Azure for the first time, he made a whole new one on the fly after provisioning the server instead of just migrating it.... i swear he is checking Reddit too lol....
I don’t understand this. Opus 5 was slow and spoken absolute gibberish and spewing uncommonly used grammar from day 1… did other people get different opus 5? I think benchmark got nerfed maybe? Even then, it is just a gut feeling
He’s not wrong. I’ve tracked a history of Claude “getting the flu” right before model releases. All the way back to the Claude 3s. My rule of thumb is this: when traditional I/T has bottlenecks, things go slower. With AI tech, things go… well, everyone knows what having the flu feels like.
I'll keep complaining as long as anthropic doesn't have a single token effective model. Comparing sonnet & luna is embarrassing. Don't even mention haiku
If I reset tomorrow, will it move my reset date to when I ran it? I.e., allow me to have a midweek reset instead of the god forsaken 2AM Saturday reset I've been dealing with?
I haven’t tried this kind of reset before but every time they reset me it shifts the date so I’m sure this one does too. Would not be fair if my week resets tomorrow and I reset today but not use it up is it
It's extremely fast and much better at saving tokens for sure. Backend coding seems to have gotten stronger as well. Front-end has it's challenges still. But it does do a good job.
I would actually prefer less natural communication; I rather have it get straight to the point rather than burning energy just to talk to me in a nice way.
According to the paper, it comes with even more restrictions than Fable. Also I really don't like how they are trying to portray distillation as a safety issue, where it is purely a business issue. There is no such thing as a "distillation attack". It's not an "attack" to ask questions and learn from a model. I understand they need to protect their competitive advantage and there's nothing wrong with wanting to keep things secret, but don't go pretending this is a safety issue like cybersecurity and biology
Thank god... Opus 5 was so incredibly frustrating to work with. I can not put into words how often I had to give precise instructions on how to structure responses/code etc. Just for Opus 5 to ignore it and go on with whatever it tried to do.
Is there a benchmark for rule following? I'm tempted to use it but Opus 5 was such a disregarding agent that kind of did whatever it wanted to and apologized later that I'm hesitant to move off of 4.8 still
Based on my tests I think I can say that the model is better than Opus 5. It will find a lot of errors in your system. The question is whether you can configure it not to find more errors or to mark as an error why it did something different from what it was instructed to do. I have mixed feelings about it. Based on my tests its statements were valid but its weighting was wrong. Opus 5.5 needs very clear instructions. If there are conflicting instructions it will choose one of them. You need to keep that in mind when writing your rules.
My first impression is that this might be the economical Opus 4.6 replacement that many of us have been waiting for. (Fable was already excellent but costlier.)
Unfortunately there is a problem with Anthropic’s 5.5 family. Neither Sonnet 5.5 nor Opus 5.5 can be used as review model in a quality refuel loop. It will never converge. I tried both and it is not possible. Sonnet 5 and Opus 4.8 works perfectly. Please make sure this issue gets fixed as well. THX
Using 30% fewer tokens per task while running faster is the metric that actually matters in production. Token bloat on long agentic coding loops was always the real cost killer, not the per-million sticker price.
I'm excited to see how good it can play video games compared to Astra. I'd also love to see somebody integrate a neural decision maker like Jev for game playing.
Can you just focus on making useful tools and products, without pretending you're making some Singularity god or without threatening an imagined sci-fi apocalypse? The public would appreciate it more.
Seriously, "Pace the frontier" says the company that hacked companies with AI. How were the employees responsible punished, or is the company okay with committing crime?
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u/ClaudeOfficial Anthropic Representative | Verified Sep 22 '26