From the GitHub release page:

This is CircuitPython 9.0.0-alpha.4, an alpha release for 9.0.0. It has significant known bugs, and will have further additions and fixes before the final release of 9.0.0.

(9.0.0-alpha.3 was discarded due to a build problem, fixed by #8587.)

NOTE: Starting with 9.0.0-alpha.4, CircuitPython uses a new internal dynamic storage mechanism (“split heap”), which will need to be tuned. You may find that some CircuitPython programs fail with MemoryError or RuntimeError: PYSTACK exhausted exceptions. Adjusting the settings.toml value CIRCUITPY_HEAP_START_SIZE may help. Please file issues with examples of programs that no longer load, and whether you were able to fix the problem by adjusting CIRCUITPY_HEAP_START_SIZE.

WARNING for nRF52 boards only: If your board has an nRF52 UF2 bootloader whose version is before 0.6.1, you will not be able to load CircuitPython 8.2.0 and later, due to increased size of the firmware. See these instructions for updating your bootloader.

Notable changes to 9.0.0

• New split-heap internal dynamic storage mechanism.
• Merge updates from MicroPython v1.19.1, v1.20.0, and v1.21.0.
• Espressif: update to ESP-IDF v5.1.
• Reorganize and split displayio. 8.x.x naming structure is available in 9.x.x, but will be removed in 10.0.0.
• CIRCUITPY drives now mount on Android.
• Increased file capacity on CIRCUITPY drives <= 128kB.
• Further USB host support, on i.MX and RP2040.
• Remove 8.x.x deprecations: displayio.*.show(), I2CPeripheral renamed to I2CTarget.
• Add repl.py, which runs just before the REPL starts up.
• Add OrderedDict.move_to_end().
• Add synthio.Synthesizer.note_state.
• Add warnings module, similar to what is in CPython.
• Add I2S MCLK support on Espressif.
• Add mDNS TXT record support.

Download from circuitpython.org

Firmware downloads are available from the downloads page on circuitpython.org. The site makes it easy to select the correct file and language for your board.

Installation

To install follow the instructions in the Welcome to CircuitPython! guide. To install the latest libraries, see this page in that guide.

Try the latest version of the Mu editor for creating and editing your CircuitPython programs and for easy access to the CircuitPython serial connection (the REPL).

Documentation

Documentation is available in readthedocs.io.

Port status

CircuitPython has a number of “ports” that are the core implementations for different microcontroller families. Stability varies on a per-port basis. As of this release, these ports are consider stable (but see Known Issues below):

• atmel-samd: Microchip SAMD21, SAMx5x
• cxd56: Sony Spresense
• espressif: Espressif ESP32, ESP32-S2, ESP32-S3, ESP32-C3
• nrf: Nordic nRF52840, nRF52833
• raspberrypi: Raspberry Pi RP2040
• stm: ST STM32F4 chip family

These ports are considered alpha and will have bugs and missing functionality:

• broadcom: Raspberry Pi boards such as RPi 4, RPi Zero 2W
• litex: fomu
• mimxrt10xx: NXP i.MX RT10xxx
• silabs: Silicon Labs MG24 family
• stm: ST non-STM32F4 chip families

Changes since 9.0.0-alpha.2

Fixes and enhancements

• Increased file capacity on CIRCUITPY drives <= 128kB. #8567. Thanks @eightycc.
• Use auto-growing split heap. #8582, #8553. Thanks @tannewt.
• CIRCUITPY drives now mount on Android. #8580. Thanks @eightycc.
• Update frozen libraries. #8577. Thanks @dhalbert.
• Fix off-by-one multiple-block flash reads when read starts at MBR. #8575, #8565. Thanks @eightycc.
• Fix incorrect type object declarations, restoring access to native class properties. #8560, #8535. Thanks @dhalbert and @deshipu.
• Add mDNS TXT record support. #8262. Thanks @thzinc.

Port and board-specific changes

Broadcom

Espressif

• I2S MCLK support on Espressif. #8586, #8571. Thanks @lookfwd.

i.MX

nRF

RP2040

• Fix pulseio.PulseIn race condition. #8575, #8505. Thanks @Snipeye.

SAMx

SiLabs

Spresense

STM

Individual boards

• Adafruit ESP32-S3 Camera: Update pins to Rev D. #8557, #8528. Thanks @ladyada.

Documentation changes

• Fix busio I2C scan example. #8575, #8568. Thanks @dhalbert.

Build and infrastructure changes

• Add lib/tlsf to ci_fetch_deps.py to fix release builds. #8587. Thanks @dhalbert.
• Updates to handle Python 3.12. #8584, #8575, #8568. Thanks @dhalbert.
• Switch to gcc 13.2. #8546. Thanks @tannewt.
• Use MP_ERROR_TEXT() instead of translate() everywhere. #8452. Thanks @jepler.
• Use mp_rom_error_text_t instead of compressed_string_t. #8531, #8519. Thanks @tannewt and @jepler.

Translation additions and improvements

• Thanks for translations:
  • @andibing (English – UK)
  • @hexthat (Chinese – Pinyin)
  • @jessyjones (French)
  • @MuskoM (Polish)
  • @supcik (French)
  • @wtuemura (Portugese – Brazil)

New boards since 9.0.0-alpha.2

• LILYGO T-Deck. #8563. Thanks @rgrizzell.
• Unexpected Maker BLING! #8575, #8495. Thanks @UnexpectedMaker.
• Unexpected Maker TinyWATCH S3. #8575, #8495. Thanks @UnexpectedMaker.
• WeAct C6 N4. #8550. Thanks @bill88t.
• WeAct C6 N8. #8550. Thanks @bill88t.

Known issues

• See https://github.com/adafruit/circuitpython/issues for other issues, including issues still to be addressed for:
  • 8.2.x
  • 9.0.0
  • long term

Thanks

Thank you to all who used, tested, and contributed since 9.0.0-alpha.2, including the contributors above, and many others on GitHub and Discord. Join us on the Discord chat to collaborate.