I started using ChatGPT in March 2023. As far as I remember, the domain name was Chat.OpenAI.com and I had to register an account. Today, a year later, OpenAI's ChatGPT is now officially ChatGPT.com, and you don't have to register an account, so how fast has it changed?

Last year OpenAI filed a UDRP against the ChatGPT.com domain. the company had been using Chat.OpenAI.com as its Chat GPT platform. in September it was shared that the dispute appeared to be settled and that ChatGPT.com had been transferred to OpenAI. for some time now the domain name has been forwarded to serve as the ChatGPT-based subdomain.

The company has now migrated its Chat GPT platform to ChatGPT.com:
If you visit chat.openai.com, you will be redirected directly to the ChatGPT.com website.
These changes indicate that OpenAI made this change because Chat GPT has grown enough to become a recognizable brand in its own right. It would be wise to operate Chat GPT on its brand-matching ChatGPT.com domain.
Source: domaininvesting