How did Kylie Jenner enhance her bum?

It look slike she had buttock augmentation.  Done by the right surgeon, buttock implants could look very natural and tasteful.  The incision in the intragluteal crease so its hidden and usually isnt noticable.

Only Kylie is truly privee to answer your question. However, I can tell you this:Regarding buttock augmentation, let me start off by saying that I currently see at least 1 - 2 patients per week that failed "brazilian buttock lift" (i.e. the fat melted away after 10 - 12 months) and are now seeking a more reliable and permanent option (i.e. buttock implants). One of the most important factors in creating the perfect derriere with implants is indeed selecting the right size AND shape. I have found the best way to assure this is to simply measure the actual dimensions of the patient’s buttock cheeks. With these anatomical measurements, I can select an implant that not only significantly augments the buttock but also supplies the correct 3-dimensional enhancement to look as real as possible. Therefore the only way for you to know what implant works best is to consult with a board certified plastic surgeon specializing in this procedure and have him/her take your measurements before selecting an implant and proceeding with surgery. The largest stock buttock implant currently available in the USA is a 690cc round implant. Indeed custom implants can be ordered larger, not only at a premium price but at a premium risk for most patients'. Unlike breast implants which are placed under the very expandable tissue of the breast and half of the pectoral major muscle, buttock implants are (most preferably) placed under (or at least within) the largest strongest muscle of the body, the gluteus maximus muscle, which is not nearly as expandable or forgiving. Thus most patients simply do not have a large enough native buttock muscle to fit an implant much over 500 ccs', without leading to significant complication such as wound breakdown/opening &/or implant exposure...necessitating removal. Some of those sought after video-vixen and celeb-types (without mentioning names) with cartoonish bottoms could have either gotten extremely lucky with a huge oversized implant (very unlikely if properly placed under the muscle), had a very large volume of filler injected such as silicone, PMMA, or hydrogel - all NOT recommended because of high risk of severe infections, migration and/or hardening over time,  and even deadly consequences in rare but significant instances (if mistakenly injected into the blood stream); and/or have been genetically "blessed" - although quite unlikely.I generally do not recommend fat grafting at the same time as placing buttock implants because of a significantly increased risk of infection. For fat to survive it must be grafted into muscle, however that is also where the implant sits. Thus, if fat it injected into the implant or implant pocket then it will die and almost assuredly get infected - necessitating removal of the implant as well. Fat transfer later on must be done very carefully and cautiously, preferably by the original surgeon, for the very same reasons as above. Nonetheless, buttock implants are a proven safe and effective method of buttock augmentation as long as the recommendations of a board certified plastic surgeon specialist are adhered to.Glad to help.

Hello dear!!
Thanks for the question and provided information as well.
In short, it looks like butt augmentation with implants and contouring with fat transfer. l recommend you to make an appointment with a board certified plastic surgeon to talk about your goals and anything you need to know.
Good luck :)