Some context: In the upcoming versions of macOS and iOS, Apple is including a predictive text model which offers suggestions while you type, which they’ve said to be a "transformer model". I managed to find some details about this model, including details about its topology (which looks a lot like GPT-2) and its tokenizer, and I was even able to peek in and see several of its top predictions while typing!
Hopefully this can give some insight into some of the trade-offs that Apple went through to put a model on every iPhone and MacBook — it’s small, it has a pretty narrow scope, and it’s not very capable on its own.