From the GitHub release page:

3.0.0 is the latest major revision of CircuitPython and features new support for the SAMD51 (aka M4) and preliminary support for the nRF52 BLE chipset. It also features better memory utilization so more can be loaded in the same amount of space.

Alpha!

This is an alpha release of 3.0.0. Alpha releases do not have the complete API from 2.x and are only meant for testing. (Beta release will have the full API but still need work.) Please use the latest stable release when first starting with CircuitPython. It is stable.

When you find a bug please check the current known issues and file an issue if something isn’t already known.

Changes since Alpha 4

• Support atmel-samd real-time clock (RTC) as main time source. Thanks @notro!
• Add audiobusio.I2SOut support and split samples into audioio.RawSample and audioio.WaveFile. Thanks @tannewt
• atmel-samd: usb_hid now includes Gamepad support. Thanks @dhalbert.
• Re-enable nvm. Thanks @tannewt
• Fix tick_delay to work without interrupts (and correctly too). Fixes DHT22. Thanks @jerryneedell and @sommersoft
• Add ItsyBitsy M4 initial support. Thanks @tannewt
• Fix status neopixel flashes. Thanks @tannewt
• Fix nrf52 build on Windows. Thanks @ladyada

Installation

To install follow the instructions in our new 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).

All builds except ESP8266 are available as both UF2 and bin files here along with test builds.

New Features in 3.0.0

• Support for SAMD51 based M4 boards from Adafruit. Thanks @tannewt, @dhalbert, @siddacious and all the M4 testers.
• Preliminary support for nRF52 BLE capable boards. Thanks @glennrub, @tralamazza, @microbuilder, @arturo182, @hathach and @jerryneedell.
• Long-lived heap allocations are better compacted. (Video) Thanks @tannewt and @dhalbert.
• Read the microcontroller’s unique id through microcontroller.cpu.uid. Thanks @sommersoft!
• UART can now be created with only one direction. Thanks @dhalbert!
• Files to prevent mac from indexing the drive are created automatically. Thanks @jepler!
• * and *= implemented for array.array. Thanks @jepler!
• Implemented seeking to non-zero locations. Thanks @aykevl and @jepler.
• Detect when USB has been plugged in with supervisor.runtime.serial_connected. Thanks @sommersoft and @dhalbert.
• Change file system label (CIRCUITPY by default) using storage.getmount("/").label.
• Add storage.erase_filesystem() to make erasing the file system easy. Thanks @dhalbert!
• atmel-samd: usb_hid support include Consumer Controls (aka multimedia keys) and Gamepad. Thanks @dhalbert.
• Support atmel-samd real-time clock (RTC) as main time source. Thanks @notro!
• Add audiobusio.I2SOut support and split samples into audioio.RawSample and audioio.WaveFile. Thanks @tannewt
• Code has been reorganized to ease sharing main code across ports.

Breaking Changes!

• ustruct has been replaced with struct to match CPython.
• The mpy format has changed so make sure and use a 3.0.0 bundle for libraries.
• Non-standard array types inherited from MicroPython are no longer supported in favor of matching CPython. Thanks to @jepler.
• audioio.AudioOut now takes the sample to playback in play rather than in the constructor. (This enables playback through other outputs such as audiobusio.I2SOut.) It also means you only need one AudioOut for multiple samples.

Thanks

Thank you to all who used, tested, contributed, helped out, and participated on GitHub and/or Discord:
@ladyada, @dhalbert, @tannewt, @kattni, @microbuilder, @arturo182, @jamesadevine, @tralamazza, @hathach, @glennrub, @siddacious, @deshipu, @tdicola, @mrmcwethy, @willingc, @sommersoft, @deanm1278, @jerryneedell, @stewmystre, @boneskull, @Sigafoos, @brentru, @caternuson, @process1183, @Andon-A, @asherlie, adamwolf, dastels, @hukuzatuna, @KurticusMaximus, nis, BravoDelta, aj_nys, @wolf, @vesperk38, @jepler, @notro, CGrover and surely more we have missed. Join us on the Discord chat to collaborate.

Documentation

Documentation is available on readthedocs.io.

Here are all the changes since 2.2.3.

This release is based on MicroPython 1.9.3. Support upstream MicroPython by purchasing a PyBoard (from Adafruit here).

Troubleshooting

Check out this guide for info on common problems with CircuitPython. If you are still having, then post to the Adafruit Support Forums and join Discord.

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Note: 3.0.0-alpha.5 was incorrectly tagged on an older commit so we’re already now alpha 6! Yay free numbers!