Preview features
uv includes opt-in preview features to provide an opportunity for community feedback and increase confidence that changes are a net-benefit before enabling them for everyone.
Enabling preview features
To enable all preview features, use the --preview flag:
Or, set the UV_PREVIEW environment variable:
To enable specific preview features, use the --preview-features flag:
The --preview-features flag can be repeated to enable multiple features:
Or, features can be provided in a comma separated list:
The UV_PREVIEW_FEATURES environment variable can be used similarly, e.g.:
For backwards compatibility, enabling preview features that do not exist will warn, but not error.
Using preview features
Often, preview features can be used without changing any preview settings if the behavior change is
gated by some sort of user interaction, For example, while pylock.toml support is in preview, you
can use uv pip install with a pylock.toml file without additional configuration because
specifying the pylock.toml file indicates you want to use the feature. However, a warning will be
displayed that the feature is in preview. The preview feature can be enabled to silence the warning.
Other preview features change behavior without changes to your use of uv. For example, when the
python-upgrade feature is enabled, the default behavior of uv python install changes to allow uv
to upgrade Python versions transparently. This feature requires enabling the preview flag for proper
usage.
Available preview features
The following preview features are available:
add-bounds: Allows configuring the default bounds foruv addinvocations.json-output: Allows--output-format jsonfor various uv commands.pylock: Allows installing frompylock.tomlfiles.python-install-default: Allows installingpythonandpython3executables.python-upgrade: Allows transparent Python version upgrades.
Disabling preview features
The --no-preview option can be used to disable preview features.