section_path: Versions/Block 4
section_name: Block 4
paragraph_text: Block 4
  
  In 2017, SpaceX started including incremental changes to the Full Thrust, internally dubbed Block 4. Initially, only the second stage was modified to Block 4 standards, flying on top of a Block 3 first stage for three missions: NROL-76 and Inmarsat-5 F5 in May 2017, and Intelsat 35e in July 2017. Block 4 was described as a transition between the Full Thrust v1.2 Block 3 and Block 5. It includes incremental engine thrust upgrades leading to Block 5. The maiden flight of the full Block 4 design (first and second stages) was the SpaceX CRS-12 mission on August 14.