Upgrade to Python 3.12

To provide additional improvements and features from Python 3.12 to our users, Colab has been upgraded to Python 3.12. This upgrade provides benefits for the packages we pre-install in our runtime, and brings Colab into alignment with the cadence of final regular bug fix releases for Python versions. We have also upgraded the torch packages to 2.8.0, since torch-xla<2.8 does not support Python 3.12.

Colab’s fallback runtime version

Using the fallback runtime version temporarily allows access to the last version of the runtime before the upgrade described above, and is available until early September. Its purpose is to provide a temporary mechanism for users to more smoothly upgrade their notebooks to be compatible with Colab’s current runtime version. This is available from the Command Palette via the "Use fallback runtime version" command when connected to a runtime. Of note, this setting does not persist across sessions – the command will need to be invoked on each new session.