The inference engine is implemented in SubL (see https://cyc.com/archives/glossary/subl/ https://cyc.com/archives/glossary/subl/ and https://web.archive.org/web

The inference engine is implemented in SubL (see https://cyc.com/archives/glossary/subl/ https://cyc.com/archives/glossary/subl/ and https://web.archive.org/web/20120513111513/http://www.cyc.com/cycdoc/ref/subl-reference.html https://web.archive.org/web/20120513111513/http://www.cyc.co...) which is a variant of Common Lisp, and the knowledge base is implemented in CycL which is divided into the Epistemological Level (EL) and the Heuristic Level (HL). There was a source-available version called OpenCyc with a small subset of the knowledge base that is now retired and no longer officially available, but it's still easy to find on the net.