Currently, Esri provides a downloadable version of the ArcGIS JS API for offline hosting. This includes core modules but does not include the new Map Components (@arcgis/map-components) or Calcite Components (@esri/calcite-components), which are only available via CDN or NPM.
It would be very useful for offline/enterprise environments if these modules could also be included in the hosted API package, or if there was a clear supported way to host them locally.
URL: https://developers.arcgis.com/javascript/latest/downloads/