"Fallback" is only for LLM-training related requests (ie, ones that would compete with Anthropic (!))
For cyber and bio related requests it just refuses.
When it was briefly available I had it fallback to Opus for security related tasks. It would only refuse if you explicitly told it not to fallback.
When it was briefly available I had it fallback to Opus for security related tasks. It would only refuse if you explicitly told it not to fallback.