Google tends to launch the latest versions of its Android OS alongside Galaxy branded devices, which means the Galaxy S4 will likely not come with the next generation of Android, which will presumably be called Android 5.0 Key Lime Pie. According to GottaBeMobile, the device will instead hit the market with the current version of the OS, Android 4.2 Jelly Bean. Benchmarks posted by GSMArena also indicate that the S IV will include Jelly Bean.

Source: GottaBeMobile, GSMArena