I've only tried Grok Code Fast 1, so I can't speak for any of the other models.

In my experience, Grok is very fast and very cheap, but only moderately intelligent. It isn't stupid, but it rarely does anything that impresses me. The reason it's a useful model is that it is very, very fast (~90 tokens per second) and is very competitively priced.

There is also code-supernova, which is in-preview improved version of grok-code-fast-1. 1M context window. It's useful, but I'm still not sure how much better than grok-code-fast-1. You can get free access to it via a few providers, e.g. opencode.

Grok 4 is extremely capable, but for everyday chatting, Grok kinda sucks since it keeps repeating what you told it, and saying the current timestamp for some reason. ChatGPT is much better with its post training and prompt I feel like.

Grok has been free for over a month now and for me it has certainly proven itself competent at most tasks that you would otherwise have to pay for with Claude, ChatGPT, etc.