Apple's still dealing with the fallout from revelations that it was deliberately (and secretly) throttling older iPhones, even if the logic behind the decision was reasonably sound.
It's all down to the battery degrading over the phone's lifespan, making power management more unstable and potentially causing unexpected shutdowns. So Apple used software to throttle the hardware and make sure that didn't happen. While government bodies across the world have reportedly started investigating the issue, there's still the lingering question of what happens about throttling in the future.
Apple has already confirmed that a software update is on the way that lets people choose whether or not their phone's speed gets throttled, but it's also confirmed that newer models won't be affected thanks to "hardware updates".
Specifically Apple means the iPhone 8, X, and presumably future models that have yet to be announced. That's what it put in a letter to US Senator John Thune, chairman of the Commerce, Science, and Transportation Committee (via Ars Technica):
“iPhone 8, iPhone 8 Plus, and iPhone X models include hardware updates that allow a more advanced performance management system that more precisely allows iOS to anticipate and avoid an unexpected shutdown.”
It doesn't detail any specifics of what these hardware updates might involve (because why would Apple reveal its secrets like that?), but it seems likely to involve the more advanced components inside the phones themselves. My guess would be the A11 Bionic chipset, which has dedicated neural network hardware inside. But that's just speculation, and unless Apple decides to make the information public we'll never know for sure.
The letter also confirms that Apple was considering a rebate for customers who paid full price for a battery replacement in a throttled phone, although it hasn't said it will absolutely definitely happen. It seems likely, though, seeing as how much of a PR fiasco this is, and the number of class-action lawsuits its facing. A rebate for the small number of customers who paid full price could earn them some good will. [Ars Technica via Ubergizmo]