I think it got divided into K-1 Global and K-1 Japan.
K-1 Global was basically trying to be like the K-1 Max from the golden days but it was kinda shitty. That shady thing with Buakaw vs Kehl was on K-1 global.
While K-1 global is dead, K-1 max is putting out very good events with most talent being under 70 kg. Some notable fighters in K-1 Japan are Kaew Fairtex, Hiramoto Ren, Masaaki Noiri, Yasuomi Soda, Takeru, Koya Urabe, Taiga, Gonnapar, Wei Rui, Chingiz Allazov.
For Kickboxing in general K-1 Japan, Glory and Kunlun Fight are the organisations to follow.
There is also Glory Of Heroes and WuLingFen which i think are a bit shady with weird decisions. OneFC a new organisation with some good fighters but their events seem a bit sporadic. Some fights are muay thai rules, some mma rules, some kickboxing rules. There is also Enfusion and Superkombat i don't personally don't think the talent level in those organisations is that great though.