An eidolon grows in size, becoming Large. The eidolon gains a +8 bonus to Strength, a +4 bonus to Constitution, and a +2 bonus to its natural armor. It takes a –2 penalty to its Dexterity. This size change also gives the creature a –1 size penalty to its AC and on attack rolls, a +1 bonus to its CMB and CMD, a –2 penalty on Fly skill checks, and a –4 penalty on Stealth skill checks. If the eidolon has the biped base form, it also gains 10-foot reach. Any reach evolutions the eidolon possesses are added to this total. The eidolon must be Medium to take this evolution. The summoner must be at least 8th level before selecting this evolution.
If 6 additional evolution points are spent, the eidolon instead becomes Huge. The eidolon gains a +16 bonus to Strength, a +8 bonus to Constitution, and a +5 bonus to its natural armor. It takes a –4 penalty to its Dexterity. This size change also give the creature a –2 size penalty to its AC and attack rolls, a +2 bonus to its CMB and CMD, 10-foot reach, a –4 penalty on Fly skill checks, and a –8 penalty on Stealth skill checks. If the eidolon has the biped base form, its reach increases to 15 feet (10 feet for all other base forms). Any reach evolutions the eidolon possesses are added to this total. These bonuses and penalties replace, and do not stack with, those gained from becoming Large. The summoner must be at least 13th level before selecting this option.
The ability increase evolution costs twice as much (4 evolution points) when adding to the Strength or Constitution scores of a Large or Huge eidolon.