I'm curious in knowing why you've opted for this model over ChatGPT-3.5. Is it because it performs better in Chinese?

Chatgpt is blocked in China including Hong Kong, so my school computer doesn't have access to it. I also am a very very casual AI user

Given I'd get through registration can I talk with it in English?

Yes.

Given the subdomain name, I presume it uses the Yi-34B model?

I have no idea, but yiyan is short for wenxinyiyan（文心一言), which roughly translates to character-heart-one-(speech/word). Maybe someone who is Chinese could translate it better. So I don't think the name has anything to do with the model.

I do wonder what their backend is. They have the same 3.5/4 version numbering scheme that ChatGPT uses, which could be just marketing (and probably is), but I wonder.

EDIT: fixed my translation

Their backend originates from Baidu ERNIE: http://research.baidu.com/Blog/index-view?id=160

“A single word from the heart”

AFAIK, model behind yiyan is Baidu's ERNIE. Yi-34B (and Yi model family) comes from another startup created by Kai-fu Lee earlier this year: 01.ai.