Currently the only cards to support 4-way SLI are the following:

GTX 285 (All 285 products with later than 196.xx drivers)

GTX480
GTX480 hydro copper FTW
GTX480 Super clocked

GTX 580
GTX 580 Superclocked.
GTX 580 HydroCopper2

All GTX 680's

All GTX 780Ti's

GTX Titan/Titan Black

GTX 970

GTX 980

GTX 980 Ti

GTX Titan X