100% beef is the topic of an ongoing lawsuit[0].
I was surprised to see a real reference because I thought the 100% beef thing was a 100% myth.
But that article confirms in several places that independent testing finds no fillers at all, and what is left is just "Plaintiffs allege that undisclosed processing steps or agents applied during production or cooking could alter the accuracy of the “100%” claim." It's not a very convincing argument and it would be quite hard for McDonalds to cover up a secret process to add another ingredient.
> Additionally, the visual gap between advertised burgers and actual burgers raises separate false advertising issues
Meanwhile, the very clear and obvious false advertising they actually perform is getting hardly any attention. Here's to hoping they won't be able to continue advertising products that are different from what they sell.