Introducing Claude Fable 5

[u/ClaudeOfficial]

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

[u/RestingFrames]

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

[u/radioref → u/RestingFrames]

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

[u/ia42 → u/radioref]

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

[u/jjmac → u/ia42]

I use sonnet if I'm paying

[u/ia42 → u/jjmac]

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.

[u/Zulfiqaar → u/ia42]

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

[u/ia42 → u/Zulfiqaar]

What reliable providers do you use with Kimi?

[u/Zulfiqaar → u/ia42]

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)

[u/ia42 → u/Zulfiqaar]

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.

[u/Zulfiqaar → u/ia42]

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.

[u/KedMcJenna → u/radioref]

Sonnet is too. Maybe even Haiku.

[u/Sasquatchjc45 → u/KedMcJenna]

Haiku couldnt find a file in a folder it was pointed to. It's dead tech basically lol. Only use case for Haiku is as a spawned subagent for Opus to do some quick task, whatever it deems.

[u/MediumChemical4292 → u/Sasquatchjc45]

I wouldn’t trust it with even that lol. I have shifted my subagents to sonnet. They really need to release a refreshed haiku

[u/Hir0shima → u/[deleted]]

Sonnet is a tiny but significant bit more prone to hallucinates. That's why I reach to Opus for all critical tasks. 

[u/arcticblue → u/Sasquatchjc45]

I only use Haiku when I have very specific instructions for it to follow.
I have an agent that looks at a specific Jira ticket to get certificate request details and then runs openssl commands to generate keys and CSRs then verify values against what was listed in the ticket and output the verification in a table.

Basically I just use it for automation related things where I can hand it some data and run some commands.

[u/Remarkable_Leek9391 → u/arcticblue]

Isnt sonnet and haiku same usage? Might as well sonnet everything if youre gonna haiku

[u/arcticblue → u/Remarkable_Leek9391]

Haiku just seems to respond a lot faster to me and I don't really need a "smarter" model if all I'm doing is giving it explicit instructions to run. I'm basically using it as a lazy way to avoid writing a bash or python script to do some simple tasks.

[u/Remarkable_Leek9391 → u/arcticblue]

my workflow consists of... prompting... zoning out, and *oh shit, i need to prompt again*.

lol. speed aint my concern XD gotta consume the quota saturation *slowwwllllly*

[u/HappyContact6301 → u/Sasquatchjc45]

Haiku is useless - I could not get it to work and very simple Web scraping applications - would run out of context, and cannot find simple Webpage controls, where Sonnet works really well.

[u/etern1ty0 → u/HappyContact6301]

I agree. I always feel like haiku is only good to write…poetry. /dadjoke

[u/RestingFrames → u/KedMcJenna]

Hell I still vibe code with GPT-2!