This software site repository URL,
http://download.eclipse.org/releases/2018-09/
provides access to the software repository for the Eclipse 2018-09 Simultaneous Release.

This repository site URL is typically pre-populated in the list of software repositories when you install the Eclipse Platform or SDK.

For more information about installing or updating software, see the Eclipse Platform Help.

NOTE: Due to structural changes you cannot update from a Mars (or prior) all-in-one package to a 2018-09 version. If interested in the technical details, see bug 332989 and bug 490515.

Updating from Photon to 2018-09 should work but is not extensively tested for all features.