Falcon 9 Block 5
What's a Block 5? SpaceX's Upgraded Falcon 9 Rocket Explained
Elon Musk stated :
The most important improvements "uprated thrust and improved legs are the most significant."
"Final Falcon 9 has a lot of minor refinements that collectively are important,"
"the F9 boosters could be used almost indefinitely, so long as there is scheduled maintenance and careful inspections. Falcon 9 Block 5 -- the final version in the series -- is the one that has the most performance and is designed for easy reuse,"
F9 rockets use TEA-TEB (Triethylaluminum-Triethylborane) to ignite their Merlin engines that give the caritistic green flame on launch.
Falcon 9 Block 5 will be the final version of the Falcon series, it is slated to fly towards the end of 2017 (First flown 11th May 2018).
Second Stage Ignition of Merlin D vacuum engine
Each F9 Block 5 is expected to fly 10 times without any major refurbishment, if SpaceX achieve this it will give them a opportunity to reduce the cost of F9 launches even lower.
The main focus of SpaceX after this is to concentrate on the manned flights using the F9 block 5 and its Dragon two capsule in 2018/19, first they need to have 7 successful launches to prove to NASA the F9 is safe to fly astronauts.
The Second big change is for SpaceX is to refocus its engineers towards the BFR super Heavy lift rocket system that is planned to be fully reusable and thus replace the F9 and the Falcon Heavy as the BFR will be so much more capable and amazingly cheaper to use than the F9. The first 'hopper' test of the BFS (Spachship section of the BFR) is expected later in 2019.