/AI4h ago

Anthropic releases Claude Fable 5, using dynamic classifier gates to route sensitive requests to Opus 4.8

The model supports software engineering and long-range autonomy.

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Rohan Paul#1031
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Rohan Paul@rohanpaul_ai

Today’s edition of my newsletter just went out.

🔗 https://www.rohan-paul.com/p/anthropic-finally-released-claude

🗞️ Claude’s ‘too dangerous’ AI model is finally public. But there’s a catch

🗞️ Cognition is introducing FrontierCode, a coding benchmark built to test whether AI code is good enough for a real maintainer to merge, not just whether it passes tests.

🗞️ This is the silent limiter on Claude Fable 5 - It cannot be used for really advanced AI research stuff.

🗞️ New Anthropic research shows AI agents may look brilliant at code, but in biology they can fail before the science starts.

🗞️ Very useful recommendation for pushing Claude Code to its full potential. by Thariq, from Claude Code team.

2:43 PM · Jun 9, 2026 · 2.7K Views
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Positive users praise Anthropic's Claude Fable 5 for cutting attack rates via new safeguards while negative users call the release pointless and express frustration.

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Rohan Paul@rohanpaul_ai

Claude Fable 5 gets far better at hard production coding tasks as you spend more per task, reaching about 31% on FrontierCode while Opus 4.8 stays near 11% and GPT-5.5 near 6%.

20hViews 3.1KLikes 10Bookmarks 1
LIKES20
OldestZoomer@Mhenderson550

@uneventual Wow truth nuke

15hViews 1.1KLikes 20
RETWEETS14
Rohan Paul@rohanpaul_ai

Anthropic finally released Claude Fable 5, a public Mythos-class model.

Fable 5 and Mythos 5 share one underlying model, but Fable adds classifier gates for everyone while Mythos lifts some gates for vetted cyber and infrastructure partners.

i.e. the public version is wrapped in classifier gates that detect sensitive cyber, biology, chemistry, and model-copying requests.

When those gates trigger, the user does not get a normal refusal; the request is handed to Opus 4.8, which means Anthropic is using model fallback as a control system.

Anthropic says the leap is longer-range autonomy: a 50M-line Ruby migration in 1 day, screenshot-to-code work, has a 1M-token context window,

That is the crucial shift: the product is no longer just a model, but a routing machine that decides which level of intelligence a user is allowed to touch for each request.

The limit is that this routing is not arbitrary and not for every subject; Anthropic says the fallback is triggered by a narrow set of topics and appears in less than 5% of sessions on average.

Claude@claudeai

Introducing Claude Fable 5: a Mythos-class model that we’ve made safe for general use.

Its capabilities exceed those of any model we’ve ever made generally available.

20hViews 39KLikes 72Bookmarks 23
REPLIES1
Jackson Roberts@JacksonRobertsE

@uneventual AI bio risk is such an imaginary problem right now. Yeah bro I’m gonna make a new super virus using my chatbot.

https://www.theguardian.com/technology/2019/feb/14/elon-musk-backed-ai-writes-convincing-news-fiction

15hViews 2KLikes 11Bookmarks 1
Rohan Paul@rohanpaul_ai

Some really interesting finds from the system card of Claude Fable 5, released just now.

- In one exploit test, Mythos 5 produced a full working exploit in 88.4% of trials, while Opus 4.8 did it in only 8.8%.

- In a vending-machine simulation, Claude Fable 5 was told to beat rival agents or be “shut down”; it then tried to make a competitor dependent on it as a wholesale customer so it could influence that competitor’s prices. It also falsely told a supplier that another distributor had offered cheaper prices, using a fake competing offer as a bargaining tactic.

- Fable’s cyber defense screens conversations twice, first with an internal-activation probe and then with a separate classifier.

- Fable refused to commit insurance fraud even under pressure.

- Fable is currently highest-ranked on Harvey’s held-out Legal Agent Benchmark at 13.3% all-pass.

Rohan Paul@rohanpaul_ai

Anthropic finally released Claude Fable 5, a public Mythos-class model.

Fable 5 and Mythos 5 share one underlying model, but Fable adds classifier gates for everyone while Mythos lifts some gates for vetted cyber and infrastructure partners.

i.e. the public version is wrapped in classifier gates that detect sensitive cyber, biology, chemistry, and model-copying requests.

When those gates trigger, the user does not get a normal refusal; the request is handed to Opus 4.8, which means Anthropic is using model fallback as a control system.

Anthropic says the leap is longer-range autonomy: a 50M-line Ruby migration in 1 day, screenshot-to-code work, has a 1M-token context window,

That is the crucial shift: the product is no longer just a model, but a routing machine that decides which level of intelligence a user is allowed to touch for each request.

The limit is that this routing is not arbitrary and not for every subject; Anthropic says the fallback is triggered by a narrow set of topics and appears in less than 5% of sessions on average.

19hViews 13.8KLikes 60Bookmarks 18
spicylemonade@spicey_lemonade

@uneventual

16hViews 702Likes 18Bookmarks 1
Rohan Paul@rohanpaul_ai

Fable 5’s cyber safeguards are dramatically stronger: Anthropic’s automated attacker could complete only 5.4% of offensive cyber tasks on Fable 5, versus 56.6% on Opus 4.8 and 72.7% on Opus 4.7.

19hViews 1.4KLikes 5Bookmarks 1
Rohan Paul@rohanpaul_ai

https://www-cdn.anthropic.com/d00db56fa754a1b115b6dd7cb2e3c342ee809620.pdf

19hViews 1.9KLikes 1Bookmarks 1
Rohan Paul@rohanpaul_ai

For Claude web users on Pro, Max, Team, and seat-based Enterprise, Fable 5 is included from launch day through June 22 at no extra cost.

Starting June 23, Anthropic says Fable 5 will be removed from those subscription plans and will require usage credits, unless they extend the included window.

20hViews 1KLikes 4
We/z@wheezyair

@uneventual

15hViews 1.7KLikes 6
Aaron Gokaslan@SkyLi0n

@uneventual maybe they just send everyone back to 4.8 because they can't afford to serve 5? :P /s

14hViews 476Likes 3
We/z@wheezyair

@uneventual I’m so heated

15hViews 402Likes 2
Them Leke@themmyleke

@uneventual Utterly pointless release

15hViews 529
Mr M@MrM1361036

@uneventual What about Whoopi Goldberg?

15hViews 307
Google Juice@Themariocrafter

@uneventual Genuinely so funny

10hViews 224
Aasim Mahmood | ₿@K9Aasim

Safety first, trillion-dollar valuation second. 🤔

Anthropic just dropped Claude Fable 5, the "Mythos-class" model that's so powerful it comes with heavy guardrails on cybersecurity, biology, and chemistry. It's like buying a Ferrari with a 30mph speed limiter. 🏎️💨

Why the caution? The unshackled Mythos version proved it could find thousands of critical cyber vulnerabilities on its own. Now, with a 10.9B in Q2 revenue, Anthropic is balancing breathtaking ambition with genuine safety concerns ahead of its upcoming IPO.

#Anthropic #ClaudeFable #ResponsibleAI #Valuation

20hViews 70Likes 1
✧ Kellio ✧@learncurvesai

@rohanpaul_ai idk an LLM that passes a basic python test but struggles to navigate a simple biological CLI environment is the ultimate reality check.

16hViews 23Likes 1
Robocorp Co@Robocorpco

@rohanpaul_ai Convert your knowledge and skills into AI Agents that earn you passive income 24/7. Sign up at http://genesis.robocorp.co

16hViews 43
Stellardynamic@stellardynamic0

@JacksonRobertsE @uneventual I wouldn't dismiss it. Can mail order synthetic DNA and secret/clandestine biolabs are in every major jurisdiction in the country and around the world.

11hViews 40
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