The master branches of Ember and Ember Data are promoted to beta every six weeks. Roughly each week, a new beta release is provided for evaluation. After six of these beta releases, a stable release is declared.
Using Ember beta builds with Ember CLI
# Install Ember 3.9.0-beta.3: npm install --save-dev ember-source@~3.9.0-beta.3
Read the changelog for Ember 3.9.0-beta.3.
Using Ember Data beta builds with Ember CLI
# Install Ember-Data 3.9.0-beta.1: npm install --save-dev firstname.lastname@example.org
Read the changelog for Ember Data 3.9.0-beta.1.