The recently viral ChatGPT shows a system prompt during registration: “system is currently at full capacity…”
Official website https://openai.com
ChatGPT is at capacity right now

Get notified when ChatGPT is back
We’ve had a lot of people come by to check out ChatGPT, and our systems are currently at capacity. If you want to be notified when we've resolved these issues, please submit your email here. In the meantime, feel free to keep checking back at chat.openai.com.
The site is too popular and temporarily unavailable for new registrations. You can try again at a different time.