The HelioML team is happy to announce the release of HelioML 0.4.0. This release included a complete restructure of the back-end of the book, which now uses Jupyter Book version 0.8.3. As part of the restructure, all the chapter numbers shifted by one; e.g. what was previously Chapter 4 is now Chapter 3. We would like to acknowledge the following people for contributing new chapters to the book since v0.3.0: Colin Small, along with collaborators Matthew R. Argall and Marek Petrik, for contributing Chapter 7 on automatically detecting magnetopause crossings in MMS data, Rafael Pires de Lima, along with collaborator Yue Chen, for contributing Chapter 8 on forecasting Megaelectron‐volt electrons inside Earth's outer radiation belt, and Téo Bloch, along with collaborators Clare Watt, Mathew Owens, Leland McInnes, and Allan R. Macneil, for contributing Chapter 9 on classifying solar wind source regions. We would also like to acknowledge Chris Holdgraf for including us in the Gallery of Jupyter Books. Sincerely, The HelioML Team