Arm announced it was sunsetting MbedOS, and suddenly the software layer under a whole shelf of Arduino boards had an expiry date. The replacement just reached a milestone worth noting: ArduinoCore-Zephyr is now at version 1.0.0, about a month after 0.9.0 pulled it out of beta.
What Arduino actually swapped out
MbedOS was the real-time operating system sitting between your sketch and the silicon on 32-bit boards like the Portenta, Giga, and Nicla families. With Arm winding it down, Arduino picked Zephyr, a Linux Foundation RTOS with a much wider board base and an active driver ecosystem. The first beta landed in late 2024. It took until July this year to hit 0.9.0, and Arduino held back the 1.0.0 label plus the automatic rollout until it had seen a month of real bug reports from people running it on hardware.
What is in the 1.0.0 release
- Zephyr base bumped to 4.4.1, which drags in upstream driver and networking fixes for free.
- Camera support on the Nicla Vision, so the onboard 2 MP sensor works from the Zephyr core instead of only the old stack.
- Support for the STM32H5F5 coprocessor inside the VENTUNO Q, Arduino's announced-but-not-yet-shipping dual-brain single-board computer.
- A long list of stability fixes across the core itself.
The whole core is Apache 2.0 on GitHub, so you can read the board definitions and see exactly which pin maps to which Zephyr device tree node. That matters more than it sounds: the usual gotcha when moving a sketch across is a peripheral that silently maps to a different pin than the MbedOS core assumed.
Build it yourself
If you have a Portenta H7 or a Nicla Vision on the bench, open the Arduino IDE, go to Board Manager, and search for the Zephyr core. Install 1.0.0 alongside your existing core rather than replacing it, then recompile one small sketch first, ideally one that touches I2C or SPI, before you migrate a thesis project or a competition robot. Watch for any library that pokes registers directly, since those are the ones that break. Full release notes and install steps are at github.com/arduino/ArduinoCore-zephyr, and the original writeup is on Hackster.
Originally published on blog.circuit.rocks.
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