Forward-looking: Apple is said to be actively working on at least two foldable iPhone prototypes after spending more than half a decade on research and development. Sources with "direct knowledge" of the matter told The Information that the two prototypes in question fold in half like a clamshell (think Motorola's Razr or Samsung's Galaxy Z Flip5).
Apple has reportedly reached out to at least one component supplier in Asia despite the devices still being in the very early stages of development.
That said, sources don't expect a foldable iPhone to be ready for mass production in 2024 or 2025, which puts 2026 as the earliest possible date for launch. Even then, that's assuming there aren't any unforeseen issues that arise between now and then. It's also entirely possible that the project never sees the light of day should it not live up to Apple's standards.
It is believed that Apple has been toying with the idea of a foldable iPhone since at least 2018. MacRumors notes that Tim Cook reportedly responded positively to a demo of an iPhone with a 7-inch display, but the company is said to be concerned about technical challenges as well as being able to offer appealing enough features to justify a high price point.
Screen durability and folding mechanisms hamstrung early foldables. Recent models have seemingly worked out the kinks with the folding mechanics but display durability remains a concern for many prospective buyers. Plastic is plastic, and plastic is easily scratched. The last thing you want on an ultra expensive smartphone is to scratch the screen with your fingernail.
Apple is also said to be working on a foldable iPad. Such a device wouldn't need to be as thin as an iPhone, nor would it need to pass as high of durability requirements as a phone. Apple engineers are reportedly focused on minimizing the crease that can form when a display is repeatedly folded, and they'd prefer a hinge mechanism that allows the iPad to lay completely flat.