They are participating this year..
Anyways, here is an excerpt from the Voice of Russia article--they kinda buried the lede...
"In spring of 2012 it became known that the Russian Air Force is to participate in the Red Flag training exercise in the fall of 2012 together with Americans. From 8 until 19 of October, Red Flag Air Combat Exercise 13-1 will be held at Nellis Air Force Base, Nevada (the exercises are numbered in accordance with the fiscal years, and exercise in the fall will be number one in the 2013 fiscal year). Like India, who participated in the Red Flag several years earlier using its Russian-made SU-30 MKI, Russia will get a chance this year to test its aircraft in realistic combat maneuvers with USAF aircraft. This chance is very important, since up until now the only Russian aircraft of the fourth generation which fought in a real combat situation against western aircraft has been the MIG -29, but the possibility of deploying it in the conditions of very specific wars of 1991 and 1999 was limited. Under such circumstances, the chance to test modernized Russian aircraft such as the SU -27 SM, SU-30M2, MIG -29SM and other strike aircraft - despite simulations, they are still against real western aircraft and pilots - is too attractive to be miss out on."
More here
Guess who's coming to Red Flag? If you said the Russians, you're right... - The DEW Line
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