Change record status: 
Project: 
Introduced in branch: 
8.1.x
Introduced in version: 
8.1.0
Description: 

The vendor directory of external dependencies has been removed from the Drupal core git repository for the 8.1.x and 8.2.x branches. This change improves Drupal 8's compatibility with a Composer-based workflow for sites.

There will not be any changes for people downloading Drupal 8 from Drupal.org. The Drupal.org packager will add dependencies to zip and tar packages.

If you're not using zip / tar files, e.g. when using a git clone, you must run composer install to get dependencies. This command can be executed on a new or existing site. See https://www.drupal.org/documentation/install/download#git for instructions.

Impacts: 
Site builders, administrators, editors
Module developers
Themers
Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done