At the moment the release candidate is available at https://github.com/odoo/odoo/tree/8.0

We are about a month away from the official v8 stable version however odoo will be upgrading their own website to v8 this week as layed out in their release cycle.  More information on the v8 release can be found here:

https://www.odoo.com/forum/help-1/question/what-is-the-status-of-odoo-v8-stable-60225