Diet Coke
Diet Coke does not use a modified form of the Coca-Cola recipe, but instead an entirely different formula. The controversial New Coke, introduced in 1985, used a version of the Diet Coke recipe that contained high fructose corn syrup and had a slightly different balance of ingredients. In 2004, Coca-Cola introduced Coca-Cola C2, which it claims tastes much closer to Coca-Cola but contains half the carbohydrates. In 2005, the company introduced Coca-Cola Zero (replaced by "Coca-Cola Zero Sugar" in 2017), a sugar-free variation of regular Coca-Cola.
Diet Pepsi
In December 2012, an AP article reported that Diet Pepsi was changing its sweetener to sucralose ahead of a major rebranding of the soft drink set for January 2013. In 2015, some people on Facebook and Twitter expressed their distaste for the new formula. In response, Pepsi revived its aspartame formulation, as "Diet Pepsi Classic Sweetener Blend" for US markets in September 2016, and it was sold alongside the new formula. According to Pepsi-Cola manufacturer/distributor Wis-Pak, PepsiCo announced plans to reformulate Diet Pepsi back to its original formula, reverting its sweetener from sucralose to aspartame. The new formulation was released marketwide on February 25, 2018.