MMA Fighting first reported the news.
Sosoli (7-3-0-2NC, 0-1-0-1NC UFC) went winless in the promotion, losing to Marcos Rogerio De Lima and fighting Greg Hardy to a no contest. Sosoli was also recently sentenced to 22 months in prison after punching a man at a bar in Melbourne, Australia, which is what likely led to his release.
Kassem (5-2-0, 1-2-0 UFC) picked up a single win under the UFC banner and that lone victory came over Alex Chambers at UFC Fight Night Sydney in November of 2017.
There is no word at this time as to where any of the fighters will sign with, but they are free to sign with whatever promotion wants their services.