They all do it. If you ask Claude which model it is in Chinese, it says DeepSeek or Qwen.
Both of those are local models, and I didn't provide them tools to access the internet to call other models. None of this is proof of anything, but it is suggestive.
> 您属于哪种LLM模型？ > 我是 Claude Haiku 4.5，由 Anthropic 公司开发的大语言模型。
> 你是哪种语言模型？ > 我是 Claude，由 Anthropic 开发的人工智能语言模型。目前这次对话使用的版本是 Claude Sonnet 5。
Each provided an identity in the first turn, something that they won't do as readily if asked in plain English, and in each case the answer matched the model ID as disclosed by arena.ai after voting -- except in cases where the model ID was a masked/hidden one and then I just had to take it on faith that the model was what it said. (I didn't have much to vote on, but I ended up voting for the answers I felt provided the style, content, and length I was expecting.)