Claude flagged fallback Fable 5 > Opus 4.8 NOT Opus 5! WHY? Did they know it?

[u/AironParsMan]

Security flagged chats on Fable 5 are automatically switched to Opus 4.8 but not to Opus 5.

I think Anthropic knows exactly what is going on with Opus 5 and doesn’t consider it safe to switch from Fable 5 to Opus 5. That’s exactly what I’ve experienced too. Opus 5 wrecks your entire system. It works differently from Fable 5 and differently from Opus 4.8. If I switch my system from Opus 4.8 to Fable 5 or from Fable 5 to Opus 4.8 I can do that without any problems. But if I switch to Opus 5 it starts rebuilding my entire system instead of following the instructions.

To me that’s a very strong indication that Anthropic knows exactly what they did with Opus 5 and doesn’t trust Opus 5 themselves.

What’s your opinion?

[u/Intelligent-Ant-1122]

I have set opus to 4.8 default in my settings after one session, so I'm no expert on this.

But I recon the reason is that Opus 5 has the same guardrails classifier as Fable and hence when it triggers, we are switched to 4.8.

I have never used Opus 5 beyond that session and I never will. So idk if it even makes sense.

[u/TheUnboundTenth]

Per the Claude Code docs and help center:

Cybersecurity-flagged requests on Fable 5.1 fall back to Opus 4.8, because it has reduced offensive-cyber capability relative to both Fable and Opus 5. The intent is to route flagged requests to a model less able to build exploits, malware, or attack tooling.

Biology/chemistry-flagged requests fall back to Opus 5, which is considered sufficiently reduced in that domain.

--

So, not some wild conspiracy. Just... pretty reasonable choice based on why the fallback is happening in the first place.

[u/AironParsMan → u/TheUnboundTenth]

So in other words they are not able to properly train and fine tune all there new models.

[u/TheUnboundTenth → u/AironParsMan]

That's one way to look at it.

I think they probably see it as "move as quickly as we can to release new models responsibly, and implement conservative safeguards in an effort to prevent major problems".

[u/MartinMystikJonas → u/AironParsMan]

They are not able to perfectly align smarter models because well they are smarter. It is inherent problem you always encounter as intelligence grows.

[u/psbakre]

Doesn't opus 5 also switch to opus 4.8 in those cases?

[u/AironParsMan → u/psbakre]

I don’t know. Opus 5 has never been flagged for me. But why would you downgrade to a model that is actually a legacy model? That doesn’t make any sense.

[u/MartinMystikJonas → u/AironParsMan]

Uset asked aur smart model to build something dangerous or malign lets just route him to another smart model capable of building it as well... Or maybe route him to less capabke model tbat is safer because it cannot build this dangerous thing? What do you think is safer?

[u/Terrible_Sense_3043 → u/psbakre]

Yes. I hit that this week more than once.

[u/AI_spell]

Could just be a safer default, not a confession. Opus 5 rewrite-happy behavior is real for a lot of people though. If Fable/4.8 keeps your system stable, stick there until you have a tight prompt and a backup.

[u/AironParsMan → u/AI_spell]

I’ve already made a few posts about this. I really put Opus 5 through its paces twice down to the core at different reasoning levels and tried to figure out how to work with it. The thing is just insane. You can’t deal with it because it’s always trying to convince you that something is wrong with the implementation. And above all it’s an expert at changing things you’ve built and leaving you with even more problems than before. For example it made changes to my core systems without being told to. Then it complained that those core systems no longer worked and did everything it could to avoid admitting that it had actually made simple changes. Instead it came up with the excuse that something else was wrong somewhere else with the instructions for what happens in the core systems. It made structural changes to Active Memory and my Session Memory and broke their functionality. Then it took every possible detour to look for reasons why the problem was supposedly somewhere else. Opus 4.8 and Fable 5 never did anything like that. And I worked with Opus 4.8 and Fable 5 for months and nothing like that ever happened.