Arm deprecated Mbed in late 2022. Arduino announced the Zephyr migration in July 2024. The first beta shipped in December 2024. The stable 0.90.0 hit in July 2026. Today it's 1.0.0. The two years of runway were not slippage; the migration covered an RTOS surface that touches every board in Arduino's portfolio and 45 million registered developers' existing sketch libraries. The beta period is done.
Zephyr is the operative word. Unlike Mbed, Zephyr is board-support-file-driven (YAML), has a composable driver model, and runs its test suite against real hardware targets through Twister -- the same properties that make firmware testable in CI rather than on a bench. The ArduinoCore abstraction sits on top, so existing Arduino sketches port without rewriting business logic. The developer who has been using Arduino as an entry point and hitting RTOS limits now has a path: graduate from the ArduinoCore layer into raw Zephyr without changing toolchains or hardware.
Mbed projects that haven't migrated are two RTOS generations behind and on a deprecated runtime. The window for a clean migration narrows with each passing quarter as the gap between Mbed's frozen feature set and Zephyr's active development widens. Arduino handing its full hardware portfolio to 1.0.0 Zephyr closes the last argument for staying on Mbed if Arduino hardware is in the mix.