My recollection is that first 50 are Block-1, next 50 Block-2, next 50 Block-3. And then for mid-life-update, Block-1 and Block-2 will be upgraded to Block-3. I don't there are any significant airframe changes to Block-1, 2 or 3, so the powerplant will remain as RD-93.
If there is a Block-4, then we might see serious airframe changes, probably in making the airframe lighter, possibly improving out-of-cockpit visibility and situational awareness, possibly new power-plant. For all intents and purposes, Block-4 could end up being a mostly different fighter, akin to F-16C vs. F-16A.