Technically Node 4 is io.js 4 after Node 0.12 was merged into io.js 3. So it's really 0.11.x -> 1.x -> 2.x -> 3.x -> 4.0.0. Except that 1.x, 2.x and 3.x weren'

Technically Node 4 is io.js 4 after Node 0.12 was merged into io.js 3. So it's really 0.11.x -> 1.x -> 2.x -> 3.x -> 4.0.0. Except that 1.x, 2.x and 3.x weren't called "Node" at the time because Joyent owns the trademark and went on to release their own 0.x release(s) until the merge happened.