Due to low sales - only 486 units last year - Lexus decided that there is no point offering a high-performance version anymore. Instead, the new IS will receive new sports versions, but none of them will wear the F nomenclature.
There is a combination of reasons why the IS-F is selling so badly, despite its incredible performance. First of course is its huge price ($61,750) that put it out of the reach of most Lexus buyers. Then there is its low fuel economy rating of 18 mpg, while the BMW M3 delivers 20 mpg.
Those of you who still want the IS-F, you still have the 2013 model year to buy one. After the 2013 model year sells out, it appears that Lexus is going to look for another alternative to challenge models like BMW M3 and Mercedes C63 AMG.