For people interested in AI research, there's nothing new here. IMO they should do a better job of referencing existing papers and techniques. The way they wrote about "adaptors" can make it seem like it's something novel, but it's actually just re-iterating vanilla LoRA. It was enough to convince one of the top-voted HackerNews comments that this was a "huge development". Benchmarks are nice though.
Rather than just pre-baking static LoRAs to ship with the base model (e.g. one global "rewrite this in a friendly style" LoRA, etc), Apple seem to have chosen a bounded set of behaviors they want to implement as LoRAs — one for each "mode" they want their base model to operate in — and then set up a pipeline where each LoRA gets fine-tuned per user, and re-fine-tuned any time the data dependencies that go into the training dataset for the given LoRA (e.g. mail, contacts, browsing history, photos, etc) would change.
In other words, Apple are using their LoRAs as the state-keepers for what will end up feeling to the user like semi-online Direct Preference Optimization. (Compare/contrast: what Character.AI does with their chatbot response ratings.)
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I'm not as sure, from what they've said here, whether they're also implying that these models are being trained in the background on-device.
It could very well be possible: training something that's only LoRA-sized, on a vertically-integrated platform optimized for low-energy ML, that sits around awake but doing nothing for 8 hours a day, might be practical. (Normally it'd require a non-quantized copy of the model, though. Maybe they'll waste even more of your iPhone's disk space by having both quantized and non-quantized copies of the model, one for fast inference and the other for dog-slow training?)
But I'm guessing they've chosen not to do this — as, even if it were practical, it would mean that any cloud-offloaded queries wouldn't have access to these models.
Instead, I'm guessing the LoRA training is triggered by the iCloud servers noticing you've pushed new data to them, and throwing a lifecycle notification into a message queue of which the LoRA training system is a consumer. The training system reduces over changes to bake out a new version of any affected training datasets; bakes out new LoRAs; and then basically dumps the resulting tensor files out into your iCloud Drive, where they end up synced to all your devices.