Many people will tell you that you cannot let a Basenji off leash. I disagree, having had two that were reliable, one that sometimes was, and two that definitely were not! My suggestion would be to go slow with this. Work on recalls with a long line or in an enclosed area. if you can get good reliability, then add distractions. Much will depend on your dog's temperament and your relationship. My first Basenji was absolutely reliable off leash, but that was over 50 years ago and my circumstances may have contributed to her obedience. I had a horse and she learned early that she could not catch me if I took off. This may have helped convince her that sticking close and obeying was a good idea.
Full disclosure, my last Basenji boy was also good off leash, but I did use an e-collar in case of need, and it saved him from being skunked on one occasion. Most of the time I did not need to use it other than to get his attention when he was far upwind of me and could not hear my call. I do not recommend e-collars unless you take the time to learn how to use one properly, and I know many on this board do not agree with using them at all. For me it made it possible for Perry to be loose on my farm and in the woods, and it made him far safer if he should accidentally get out the door without the collar on, as happened several times over the years. Being free did not excite him and all I had to do when it happened was say "Perry, you forgot your collar" to have him return to have me put it on. He liked his collar because it meant he would be running free instead of being on a leash.
Once you are confident that your dog has a good recall, it's useful to play a bit of "hide and seek". I would wait until my boy was distracted, then duck out of sight behind trees or in brush. Once he noticed I wasn't in view he would dash about looking for me, and I would reward with praise and sometimes treats when found. Sometimes if he was looking in the wrong direction I would step out and call him, which resulted in a very fast recall and a relieved dog!