This is the 2.x branch, not really supported or actively developed as of 2018.
Support for 2.x is still possible by request but at the moment we have zero customers running 2.x builds :)
Sphinx 3.0 is now available at http://sphinxsearch.com/downloads/current/ and it is the suggested and actively maintained release.
The sources for 3.0 will also be posted here when we decide to make those publicly available.
If you need source access to 3.0 right now (commercial/delayed FOSS mode), please contact via http://sphinxsearch.com/about/contact/ or email me directly at shodan (at) sphinxsearch (dot) com