the new upstream version you refer to is no longer released under GPL, also only binaries are made available. please see comment of the project author at http://sphinxsearch.com/blog/2017/12/18/sphinx-3-0-1-released/#comment-1501196
manticoresearch is a fork based on the sphinxsearch 2.x branch released under GPL 2.0. manticoresearch has been developed steadily since mid of 2017. take a look at https://manticoresearch.com/ and https://github.com/manticoresoftware/manticoresearch it would be great seeing manticoresearch replace sphinxsearch in the next Debian releases. -- regards, Pawel Kudzia
