Release candidates are now available for JupyterLab 3.0, and can be installed with
python -m pip install jupyterlab --pre
conda / mamba
conda install -c conda-forge/label/jupyterlab_rc -c conda-forge/label/jupyterlab_server_rc -c conda-forge jupyterlab=3
Alternatively there is also this gist to test on Binder directly:
The gist will be updated to target the latest release candidate.