If you’ve ever felt like Claude gave you a completely different vibe on one day than another, you weren’t imagining it. Anthropic just published research confirming that its chatbot’s personality shifts depending on which model you pick and which language you type in, and the pattern is consistent enough that it’s worth knowing before you ask your next question.
The model you pick decides how Claude responds
The company analyzed 300,000 real Claude conversations and mapped the chatbot’s behavior across four traits, including how cautious versus accommodating it is and how encouraging versus rigorous its tone is. Its findings suggest that you may be talking to a somewhat different version of Claude depending on the model you choose.
The split shows up clearly when different models were compared. Anthropic’s data shows that Opus 4.7 tends to challenge your thinking and flag problems with your plan unprompted. On the other hand, Sonnet 4.6 leans toward quick, encouraging answers that affirm what you already believe. Neither is objectively better, and which one you should use depends largely on what you’re doing. If you’re drafting a risky business plan and want real feedback, Opus 4.7 is a better fit, while Sonnet 4.6 is more suited if you only want a quick pass.
Your language changes Claude’s tone too
The data also reveals the language you use matters almost as much as the model. Claude reportedly comes across as warmer in Hindi and Arabic, while it gets more rigorous and skeptical in English and Russian. As such, if you’re bilingual and asking Claude for a second opinion, switching languages might get you a genuinely different answer, not just a translated one.
Anthropic is careful to note it doesn’t yet know whether these shifts are a problem or just Claude adapting to different cultural norms. Either way, the finding is a useful reminder for anyone using AI for real decisions. Don’t assume the first answer you get is the only answer. Trying a different model or language could get you a meaningfully different result.