Potato starch and tapioca starch are clean, healthy thickeners you can use made from primal foods.
Xanthan gum works well but...it's questionable in nature. It's also brutal on my friend's IBS. The slightest drop has her running for the bathroom, and I believe it's a corn byproduct. I use it to make chocolate syrup because it takes like 1/2 tsp to thicken a whole pint of it, but I don't have any food sensitivities. Potato and tapioca are superior choices.
Of course, the best of all is UNFLAVORED GELATIN! Think Knox Gelatin in the baking aisle. It's made from cow bones. It's difficult to use compared to starches, but it is FANTASTIC in ice cream to keep it from freezing hard and since it's ground up cow bones it's probably the best for health! My guess is it would suck in chili.
I don't use thickeners in chili, I just reduce it. However, since it's chili, cocoa powder may help since chocolate rocks in chili!
Don't put your trust in anyone on this forum, including me. You are the key to your own success.