It was announced on their blog but the module IPython was split in many modules. Here is the list I needed to install while upgrading to Jupyter 4.0.
ipykernel ipython ipython_genutils ipywidgets jupyter jupyter_client jupyter_core jupyter-console nbformat nbconvert notebook path.py pickleshare qtconsole simplegeneric traitlets
With Anaconda, you get all these updates by typing: conda install jupyter.
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