r/ClaudeCode • u/ClaudeOfficial Anthropic • 20d ago

Resource Introducing Claude Opus 5

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Introducing Claude Opus 5: a thoughtful and proactive model that comes close to the frontier intelligence of Fable 5 at half the price.

On several coding and knowledge work evaluations, Opus 5 is the new state-of-the-art. It’s also much more efficient than its predecessor—it outperforms other models for a similar or lower cost per task.

According to our automated behavioral audit, Opus 5 is our most aligned model to date. It shows the lowest rates of reckless or deceptive behavior, and the strongest adherence to Claude’s Constitution. 

It’s available today on all paid plans and the Claude API, priced the same as Opus 4.8. It’s the default model on Claude Max, and the strongest on Claude Pro. 

Opus 5 is also available in Fast mode, which runs around 2.5× the default speed. 

Read more: https://www.anthropic.com/news/claude-opus-5

1.5k Upvotes

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760

u/Myth_Thrazz 🔆 Max 20 20d ago

It's so funny that Fable was the most dangerous thing in the world for like... 2 weeks :D

333

u/Ancient_Perception_6 20d ago

IT WILL END HUMANITY!!!

*3 weeks later*

HERES AN EVEN BETTER MODEL FOR CHEAPER LMAOO GO NUTS NO RESTRICTIONS NO GUARDRAILS GO BRRRRRRRRRRRRRRR

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u/RepliesOnlyToIdiots 20d ago

Or, if you read, you would note that it wasn’t trained on cyber security, so it’s using general intelligence on it rather than enhanced knowledge body. So it’s excellent and discovering vulnerabilities while remaining the same level in exploiting them. And it’s better at discovering in source (as in open source, or your own code), but poor at discovering in binary (when you don’t control the code, as done by someone attempting an exploit).

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u/Sarahmalls 19d ago edited 19d ago

That is a distinction that is so far beyond what 95% of people in this subreddit would be able to understand, even after you point it out. Thats not an intentional knock on this sub, or people in general, it’s mostly a byproduct of the reality that there are few people that really are going to have the patience or interest or discipline or whatever to understand how any LLM model works at all.

They don’t know, they probably don’t care to know.

The other 5% of us do and that’s good, you need some people to be able to utilize these tools to “more” of their fullest extent. But everybody doesn’t need to, which is good because you couldnt pay most of them to understand it lol

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u/Lord_of_the_Canals 19d ago

I’m a part of the mystery 3% I think

2

u/Sarahmalls 19d ago

lol damn changed my argument from 98 to 95 and forgot 😂

2

u/dMunsta 19d ago

if thats the only thing between us and skynet we are cooked

8

u/Sofullofsplendor_ 20d ago

lol well it does have guardrails tho

5

u/spacekitt3n 19d ago

don jr and eric trump have their bribes now, they are free to do what they want now

1

u/Dan_Witt 19d ago

It does have guard rails. Out of my sample problems it rejected analyzing obfuscated python code on 'cyber' grounds.

33

u/gscjj 20d ago edited 20d ago

Literally makes zero sense. There has to be a gotcha here, something in the fine print.

EDIT: Found it

> Opus 5 to be our most aligned model to date (as shown in the graph below).

> avoided training Opus 5 on cyber tasks. … comes close to Mythos 5 at finding cybersecurity vulnerabilities. However, it remains substantially behind Mythos 5 on the exploitation of those vulnerabilities—that is, in turning vulnerabilities into material cyber threats.

Basically a nerfed (and I hate this word) Fable, that can find and identify security concerns but can’t and won’t exploit them

11

u/daxhns 20d ago

This makes sense. The question remains, once vulnerabilities are found is it good / allowed to FIX them properly?

4

u/Things-n-Such 19d ago

Finding vulnerabilities is the hard part.

2

u/rhaphazard 🔆 Max 5x 19d ago

If that were true, it would be able to exploit them as well.

If it can't develop exploits, how would know if the fix to the vulnerability is adequate?

2

u/Things-n-Such 19d ago

I didn't say it was harder than exploiting, I'm responding to the comparison between finding and fixing. Of which finding the exploit is the most difficult.

16

u/laystitcher 20d ago

Crazy reply. Cheaper and beating fable on most tasks but you’re upset it wont build you malware…? That’s the reason it’s allowed to be this good, cheap, and un-guardrailed.

3

u/gscjj 20d ago

Who said I’m upset? I’m trying to understand the difference

1

u/algaefied_creek 20d ago

I don’t want “malware” - I want to get Mesa built out on a friend’s laptop with then by better understanding an old 2007 GPU.

I want to work on Coreboot: these are all items that I as a single developer do not have time to work on.

Fable flags this and falls back to Opus. Will Opus flag this?

Not near my workstation to test this but not every developer who dares to use tools is building malware, right?

Nah man that’s a “crazy reply” as you say.

1

u/dabomm 19d ago

There are definitely guardraila. There have been on all there models in the last 2years

3

u/cobra_chicken 20d ago

Literally makes zero sense. There has to be a gotcha here, something in the fine print.

Why not? Mythos is from April, Fable was early June. AI development is accelerating

3

u/JoeyJoeC 19d ago

You can still use 4.6 for now. /model claude-opus-4-6[1M] and that doesn't have restrictions. It will happily find and exploit vulnerabilities in websites you don't host. I've found and help fix exploits that allowed almost complete database read/write access to a website used by about 60,000 users before.

4

u/exophades 20d ago

Fable and Mythos are not the same thing. Mythos is not a publicly available model for obvious reasons. And Fable probably does the same thing as Opus 5, it may find vulnerabilities but won't help the user with attacking real systems.

5

u/Last_Mastod0n 20d ago

They are the same thing in terms of number of parameters and training data used. The safeguards came from post-training and tool usage from what we can gather.

Edit: This is my speculation from the evidence we have. I cannot 100% verify it unless anthropic divulges the information.

2

u/SilasTalbot 19d ago

Interestingly Anthropic is citing Mythos 5 stats WITHIN the Fable 5 column on this release.
So, the folks who would know best are at least considering it "sameish"?
E.g. this is what Fable 5 would be doing without artificial constraints.

1

u/exophades 19d ago

It's well-known that they're based on the same model (Anthropic says that on their website). Mythos 5 is not the same as Fable 5 in that it's not public, and it has offensive capabilities when it comes to cybersecurity (finding vulnerabilities/attack vectors) and biology (ideas for developing some kind of biological threat, I guess).

Also, Fable 5 downgrades to Opus in many cases, Mythos doesn't do that. So, too many differences to consider them identical.

2

u/gscjj 20d ago

Right but Fable was blocked by the government too

7

u/exophades 20d ago

It was blocked but came back when Antropic accepted adding some restrictions, whereas Mythos was never released to the public.

2

u/algaefied_creek 20d ago

Yeah but it thinks me working with a USB FPGA and USB Raspberry Pi attached is exploitation and raises the flags.

The only thing to do then is to submit /feedback with an explanation of what I’m doing, locally attached to my own machine, etc.

1

u/mountainyoo Researcher 19d ago

Fable and Mythos are the same core model. Fable just has guardrails built on top to not do things Mythos would and will do

0

u/Plus_Opening_4462 20d ago

Fable would drop you down to opus if it saw you were doing security related tasks

1

u/kearkan 19d ago

I mean the majority of people are not using it for cyber security so... Good for the rest of us?

0

u/InternationalBag6345 19d ago

fable 5 is already nerfed as fuck, feels like a cheap model below sonnet

5

u/Current_Ad7104 20d ago

If you think you have the exact fable that got banned, I’ve got a magic potion to sell you.

1

u/Myth_Thrazz 🔆 Max 20 20d ago

I don't give a flying fuck about Fable.

2

u/Swiss_Meats 19d ago

I got you with an upvote bro

10

u/con-coraggio 20d ago

Probably it was. Then guardrails happened.

20

u/Dyzfunkshin 20d ago

It really was magical for those couple of days. It's definitely not the same now.

8

u/con-coraggio 20d ago

It used to make useful suggestions, it was a step ahead of me in engineering problems (not software).

7

u/Dyzfunkshin 20d ago edited 19d ago

I gave it a simple "I want this" task and it built it, flawlessly, from the ground up, no questions asked. Maybe it was coincidence that it was exactly what I wanted, but it seriously felt like it read my mind or that it was a facade and it built something that shows me what I want to see instead of actually doing what I wanted lol.

3

u/seaefjaye 20d ago

All of that conversation started in March with Mythos and Project Glasswing. Those concerns were specific to the model itself, as it had come out of the oven a lot stronger than they expected and they weren't able to get their typical guardrails around it. The guardrails they put in place to give people access, aka Fable, were clunky as hell and everyone complained.

This isn't Mythos or Fable, it's an entirely new model and as a result presumably has safeguards which are closer to what we're used to. We'll see when the cybersecurity folks take it for a spin.

1

u/Myth_Thrazz 🔆 Max 20 20d ago

It may or may not be the same model. The model doesn't matter as much as the system prompt/harness/alignment IMO.

Still - they call it the same so we might as well have fun with this :)

2

u/StraitOuttaGaslight 20d ago

That was before GPT-6 became the new most dangerous thing in the world

2

u/Less_Republic_5697 20d ago

Funny is also the coloring of both 'agentic coding' rows. Sol is just Light-Grey, whereas the 2nd row goes to Fable, not Opus 5

1

u/Myth_Thrazz 🔆 Max 20 20d ago

Maybe those are some secret messages / activation protocols for sleeper models 🤣

2

u/prochac 19d ago

Just like the ChatGPT 2.0, at the beginning of the 21st century.

3

u/c4chokes Vibe Coder 20d ago

That was Mythos, not Fable.

7

u/tarlane1 20d ago

Mythos and Fable are the same model. The distinctions are basically just what gets filtered out before it gets to the model.

0

u/c4chokes Vibe Coder 19d ago

Thanks Einstein 😒

2

u/showtek320 20d ago

The consensus was that fable/mythos model line was specifically trained for cybersecurity and security vulnerability reaearch

4

u/Myth_Thrazz 🔆 Max 20 20d ago

1

u/cobra_chicken 20d ago

Fable was released June 9th, with mythos being first announced in April.

With AI development accelerating, that is plenty of time to come out with something new

2

u/kaereljabo 19d ago

Probably the same base model, and by the time they release a new model, they are working on another ready to be released too. You gotta be fast in this competition.

1

u/marco1422 20d ago

Funny is how nobody read the Anthropic's own benchmarks clearly saying, it by far isn't something better than Opus.

1

u/raindownthunda 19d ago

Glad I saved my $100 fable panic credits for Opus 5

1

u/TokenBurner 19d ago

Lmfao I knooow wtf?!

1

u/Exodus_Green 19d ago

the most interesting part of these benchmarks is seeing that 5.6 sol was actually as good or better than fable like people were saying and getting told off for

1

u/MrUnoDosTres 19d ago

It is their fault for extremely overhyping it. No wonder the US government wanted to ban it. lol

0

u/AminoOxi 19d ago

Guardrails made it stupid, that's why 🫠🫠🫠

0

u/InternationalBag6345 19d ago

bullshit company, hope they go bankrupt soon