Arguably Apple does prefer to use in-house models and their OpenAI involvement was said to be more "knowledge transfer" than any concrete plans to rely on OpenAI models. Microsoft definitely heavily uses ChatGPT, but also has their fingers in plenty of pies, including their in-house Phi series of SLM models and rumors of a ChatGPT hard fork (as the one company most allowed to hard fork ChatGPT when they feel like it).