I want to import content I have 2 sites running Drupal 8; the first one is a Drupal 8 beta 10 site, while the second one is a Drupal 8.0.5 site.

I made many changes to content types, but almost all the fields are identical (such as body, date, entity reference).

How can I import all the content from the first to the second one? In Drupal 7, I could use node_import, which doesn't exist in Drupal 8.
In time Drupal will have Drupal 8 -> Drupal 8 migration, but it will be a while since migration from D6 and D7 is more important. Right now there aren't any easy solutions for this.

The most sound solution would be to create a service on the beta site that exposes the data on the beta site and create a script that fetches this.

You can use RELAXed Web Services to help creating webservice on the beta site.