I just tried their API mistral-medium model for some coding prompts that failed miserably on anything other than gpt-4 and it handled them well. Just anecdotal, didn't so any proper benchmarking.
IIUC their open Mixtral 8x7 maps to the mistral-small model (which while impressive is still behind gpt-4).
I guess they want to keep their best model behind the API for now.
Anyway, I second that Mistral does stand a good chance to compete with openai