36.445% ban rate published by Jagex on reddit AMA.
Beware of the "Anti-ban" it's just a hoax us scripters tell you to buy our shit. The only real anti-ban is something that completely randomizes every action every time it does it and I doubt 99% of scripters on here could solve such an enigma.
Jagex bans are based on pattern detection. If it notices several players using the same exact pattern of actions it will essentially tell the back-end "hey look out for this pattern in the future". When it comes across that pattern a few more times it analyzes it for similarities and if there is a certain percentage of matches, a ban is served.
This is why private scripts and scripts you write for yourself will serve you best. Without several people using it, the back-end only has YOUR pattern to pick up on, meaning it can't match the required percentage and the most likely way to get banned using private scripts is by a JMod personally witnessing you, or being reported by several players in-game.