• Just In Time compilation (MJIT)
  • Endless ranges
  • Array#union and Array#difference
  • Array#filter is a new alias for Array#select
  • Enumerable#to_h now accepts a block that maps keys to values
  • Hash#merge, merge! now accept multiple arguments
  • The #then method
  • Random.bytes
  • Proc#call is now around 1.4x faster.
  • Reduce the memory footprint of short-living memory objects

Source: Whats new in Ruby 2.6?

Some nice quality of life improvements, but nothing incredibly Earth-shaking.