Does anyone know what Apple's "Private Cloud Compute" servers actually are? I recall murmurings about racked M chips or some custom datacenter-only variant? I'

Does anyone know what Apple's "Private Cloud Compute" servers actually are? I recall murmurings about racked M chips or some custom datacenter-only variant? I'm really curious how Apple is bridging the gap between consumer silicon and the datacenter scale stack they must have to run a customized Gemini model for millions of users. RDMA over Thunderbolt is cool for small lab clusters but they must be using something else in the datacenter, right?