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Long answer:
08-10 IS F are the same as 06-10 and 11-13 non-Sport Package ISx50.
11-14 IS F are the same as 11-13 ISx50 with Sport suspension (F-Sport, etc.).
I would think they are just a slightly different length. Likely would fit, but there were other changes to the rear suspension than just that one arm (knuckle and at least one of the other arms are also different).