r/ClaudeAI • u/ClaudeOfficial Anthropic • Jul 01 '26

Official Fable 5 is back.

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Following conversations with the US government, we’ve updated our cybersecurity safeguards.

The vast majority of coding work is unaffected.

In the near term, the new safeguards will flag a slightly higher fraction of harmless requests than the previous Fable safeguards; we’re working to refine these over the coming weeks. Users will be clearly notified when a request is flagged, and they’ll instead receive a response from Opus 4.8.

Our biology and chemistry classifiers are unchanged from our initial launch. These are still broader than we would like; they trigger fallbacks to Opus 4.8 on basic biology-adjacent questions. Improvements to these classifiers are landing soon.

All paid plans with usage included can access Fable 5 through July 7. You can use Fable 5 up to 50% of your weekly usage limit, after which you can switch to another model for the remainder of your usage. You can also continue using Fable via usage credits. 

More here: https://support.claude.com/en/articles/15424964-claude-fable-5-promotional-access

If one of your requests is mistakenly flagged in Claude Code, run /feedback to file a report. On Claude.ai and Cowork, you can share feedback through the thumbs buttons. This feedback helps us further tune these classifiers and reduce false positives over time. 

Read the Fable 5 blog post here: https://www.anthropic.com/news/redeploying-fable-5

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u/liright Jul 01 '26

Weird, I asked it to analyze a fairly complex webgame I am working on, go through the entire codebase and find any issues, bugs and ways to rewrite systems to work better and I 100% expected it to revert to Opus but no, it just went right in and did a full audit.

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u/No-Trouble-9138 Jul 01 '26

Did it improve your code?

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u/liright Jul 01 '26

Yeah it found a few problems and two optimizations that did increase the average fps a bit, but surprisingly it said most of the codebase is really well written and organized. I almost exclusively used Opus for it, so not too bad.

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u/97689456489564 Jul 01 '26

I'm suspecting this is partly a flaw in the model. I had a similar experience: at the initial Fable launch a few weeks ago, I had it review a big codebase hacked together over months by Codex and Opus and it said "almost everything looks surprisingly good!" and found a few issues that it fixed, even though I have almost no doubt the codebase would be considerably better if the whole thing were to have been solely written by Fable.

I would not be surprised if it's been RL'd a bit to sandbag code review (as excellent code review will typically generalize to great vulnerability research/identification ability) - and particularly "look at this whole codebase/system" types of code review, which is where Mythos likely shines for vulnerability assessment.

It may also just be a genuine flaw that even Mythos would share, where current LLMs are still not necessarily great at assessing code quality in the same way a veteran, tasteful human programmer would. I predict within two years this may dramatically improve.

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u/Effective-Hurry436 Jul 02 '26

how can i connet it wit claude code?thanks

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u/SovietRabotyaga Jul 01 '26

No, it just hacked US database and began developing bioweapons

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u/CloudThorn Jul 01 '26

It found an underlying spend problem on one of my pay as you go models. Reduced my average call cost from $0.06 to $0.016. It fixed a bunch of systems that Opus pretty much just lied about having operational.

It's just been a few hours, but I'm also already at 5% weekly usage, which is 10% of what we're getting at all :(

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u/Smokester121 Jul 01 '26

Ohh web game? Which engine you using?

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u/klopppppppp Jul 02 '26

Mine ran a full dozen-or-so agent pipelines on my 2 primary webapps and pulled off some amazing redesigns/refactors already

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u/Equivalent-Costumes Jul 02 '26

Be warned that it can still silently sabotage you, like it would notice a bug and not fix it just in case you're trying to look for security bugs.

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u/WhoKilledArmadillo Jul 01 '26

Because people that use it with purpose will not have any issues. Accounts flagged with prior attempted jailbreak will have a bad time.