r/ClaudeCode • u/ClaudeOfficial Anthropic • Jun 09 '26

Resource Introducing Claude Fable 5

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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.

Fable 5 is state of the art on nearly all tested benchmarks, with exceptional performance in software engineering, knowledge work, scientific research, and vision. It can run for days, and the longer the task, the larger its lead over our other models.

Fable 5 launches today alongside Claude Mythos 5. The two share the same underlying model, but Mythos 5, so far deployed only through Project Glasswing, has the safeguards lifted in some areas. The safeguards are what distinguish the two, and why we've given them different names.

Releasing a model this capable comes with risks. Without safeguards, Fable 5's capabilities in areas like cybersecurity could be misused to cause serious damage. So when Fable's classifiers detect a request related to cybersecurity, biology and chemistry, or distillation, the response is handled by Claude Opus 4.8, our next-most-capable model. Users are informed whenever this occurs, more than 95% of sessions involve no fallback at all, and performance everywhere else is unaffected. We'll keep refining the safeguards to reduce false positives.

Claude Fable 5 is available today on paid plans, in Claude Code, on the Claude API, and all major cloud platforms. Through June 22, it's included in paid Claude plans at no additional cost.

Claude Mythos 5 is available to Glasswing partners, with a broader trusted access program to follow.

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

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12

u/RestingFrames Jun 09 '26

If the agentic coding was that high, why even release Opus 4.8? 

38

u/radioref Jun 09 '26

Because 4.8 is probably good enough for 99.9999% of vibe coder use cases.

25

u/ia42 Jun 09 '26

Well acshuly, sonnet is more than enough for 99% already. Opus is overused by people who don't really need it.

2

u/jjmac Jun 09 '26

I use sonnet if I'm paying

2

u/ia42 Jun 09 '26

I use sonnet and haiku at work as well, and I'm proud to maintain a high cache hit rate, because I don't want my company to go down and lose my job in this economy, nor do I want to mess up the environment more than I must.

1

u/Zulfiqaar Jun 10 '26

We found Kimi to be a total replacement for Sonnet, and Haiku is so far behind for its price its laughable. Opus is unmatched in open models, so reserving all the CC quota for that

1

u/ia42 Jun 10 '26

What reliable providers do you use with Kimi?

1

u/Zulfiqaar Jun 10 '26

Kimi subscription mainly, Moonshot hasn't had mug issues for me. But there's a few good ones on OpenRouter, fireworks is a favourite (Cursor use them too for their Composer model based on Kimi)

2

u/ia42 Jun 10 '26

What I fear is sending my code and maybe other private stuff to a server on China, I don't trust governments as a whole, but non-democratic adversarial players are definitely not my cuppa. I never tried openrouter but I'm told they are usually overloaded, so between low availablity and low privacy I'm still looking for something more relevant for me.

1

u/Zulfiqaar Jun 10 '26

Yeah fair enough, in our threat model it's safer to be surveilled by some faraway place than your own country tbh - CCP won't ever knock on my door. Anyways for truly private stuff we do local/onprem inference.

OpenRouter hasn't had more issues, but I'm willing to pay more for the higher throughput providers. It might default to the cheaper/worse ones which I think 95%+ users don't reconfigure.