This is the first stable release of the Search API Solr Search module. It contains several bug fixes compared to the last release candidate (RC 5), as well as two small new features.
Especially interesting might be that the module now contains all required config files (#1896080: Include elevate.xml and other required config files), while it previously implicitly assumed/required that Solr's example config files would be present. This is also good since some of the example config files contain unwanted definitions. See the note in the Setting up Solr handbook page for details.
(If your existing Solr server is already running fine, you don't need to change the config files, except to maybe eliminate unwanted example definitions.)
There were no other config file changes since RC 5.
Users who use the "More Like This" feature on their site and are using, or plan to use, Solr 4.x, should also make sure to check out #2004596: MLT not working with Solr 4.x. Though a workaround was committed, the feature's functionality is currently severely restricted. Please discuss in this issue how this can or should be fixed.
Please also note in this context, that Solr 4.3+ is currently not completely supported by this module yet: #1992806: Fix wrong path to contrib dir in 4.x. There is an easy workaround, though, explained in the Setting up Solr handbook page.
Also interesting, if you are using HTTP Authentication, might be that you now don't need to re-enter the password every time you save the server settings (#1884312: Default password not set when editing existing server with HTTP authentication).