GPT-6.1 Sol Ultrafast also uses Nvidia hardware, not Cerebras, just far better provisioned vs how they usually provide inference allowing for higher throughput.
"Much better provisioned" might be overselling it. Mainly they are just serving very few customers per Nvidia GPU, which is an expensive solution to the problem.
So then how is OpenAI using Cerebras? Or are they not?
Or, from a different perspective: who is using Cerebras for what purpose?