CircuitPython support is currently under development. Adafruit has digital IO, analog in/out, I2C, SPI, PWM working with more items on the way. Arduino is supported through the STM32duino. There's no auto-reset bootloader support, so the user has to pull the BOOT0 pin high and manually reset before uploading. MicroPython support is very solid, but Adafruit does not provide MicroPython libraries for sensors. This board is an extraordinarily fast Feather and is Adafruit's first foray into the STM32.