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.

Beta!

This is an beta release of 3.0.0. It has the full functionality of 2.x on M0 boards but has API changes and potentially bugs. 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 6

• A number of ESP8266 fixes. Thanks @sommersoft, @jerryneedell and @larsks!
• CircuitPython and Blinka logos are now in logo. Thanks @tannewt and @deshipu
• Improve RTC precision on SAMD21. Thanks @notro
• Re-enable audiobusio.PDMIn with frequency renamed to sample_rate. Thanks @tannewt
• microcontroller.cpu.temperature implemented on SAMD21 and SAMD51. Thanks @dhalbert
• ubinascii is renamed binascii to match CPython. Thanks @jepler
• samd.clock add to enable low level clock tuning. Thanks @notro
• CPU cache enabled on SAMD51 leading to 1-2x speed improvement. Thanks @dhalbert and @WestfW
• AudioOut and I2SOut now support pause and resume while playing back a sample. Thanks @tannewt
• Support kwargs in bitbangio. Thanks @deanm1278
• nRF52 build now includes framebuf, binascii and hashlib thanks to @jepler
• Makefile improvements around selecting Python build. Thanks @rhooper
• Doc improvements thanks to @wickedchicken and @kattni
• Top-level Makefile builds sphinx docs thanks to @khawley
• OSErrors are now more human friendly thanks to @godlygeek
• ucollections has been replaced with collections to match CPython. Thanks @bildzeitung.
• supervisor.reload() now available to reload the VM. It no longer uses KeyboardInterruptException but rather its own ReloadException. Thanks to @rhooper
• Trinket M0 and Gemma M0 builds no longer include pin objects for all microcontroller pins. They only include those used by the board. Thanks to @rhooper
• Add board.I2C(), board.SPI() and board.UART() as singleton objects for default buses as defined on the board. Thanks to @matt-land
• bitbangio.I2C now has timeout kwarg to set max clock stretch wait time. Thanks to @jerryneedell
• Longints are now supported on M0 Express boards (along with M4 boards). Thanks to @notro and @dhalbert
• Add custom board for CircuitPlayground Crickit. Thanks to @dhalbert and @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
• AudioOut and I2SOut now support pause and resume while playing back a sample. Thanks @tannewt
• samd.clock added to enable low level clock tuning. Thanks @notro
• supervisor.reload() now available to reload the VM. It no longer uses KeyboardInterruptException but rather its own ReloadException. Thanks to @rhooper
• Add board.I2C(), board.SPI() and board.UART() as singleton objects for default buses as defined on the board. Thanks to @matt-land
• Longints are now supported on M0 Express boards (along with M4 boards). Thanks to @notro and @dhalbert
• Add custom board for CircuitPlayground Crickit. Thanks to @dhalbert and @ladyada
• Code has been reorganized to ease sharing main code across ports.

Breaking Changes!

• ustruct has been replaced with struct to match CPython.
• ucollections has been replaced with collections to match CPython. Thanks @bildzeitung.
• ubinascii is renamed binascii to match CPython. Thanks @jepler
• 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.
• PDMIn‘s frequency property has been renamed to sample_rate.
• Trinket M0 and Gemma M0 builds no longer include pin objects for all microcontroller pins. They only include those used by the board. Thanks to @rhooper
• Auto-reload no longer uses KeyboardInterruptException but rather its own ReloadException. Thanks to @rhooper

Thanks

Thank you to all who used, tested, contributed, helped out, and participated on GitHub, sprinted with us at PyCon and/or chatted with us on 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, @larsks, @WestfW, @rhooper, @khawley, @godlygeek, @bildzeitung, @matt-land, @wickedchicken, @margaret, sdw_nj, @ntoll, MikeBarela, Josh, Les, @cefn, (from PyCon sprints) Dylan W, Anders, David, Dylan H, Adam, John, Chris, Lady Red, Craig, Aaron, John, Boris, Drew and Kathryn 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 2.3.1.

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.