The term dire seems to have been dropped on many creatures and replaced with giant, so a dire rat is now a giant rat.
The giant variants are rather arbitrary and change conceptually as opposed to based on a template.
Giant owl goes up three size categories, gains +10 strength and +6 intelligence, but only +2 HD and no speed increase. It kind of makes sense.Here is a link to the PF dire template. In 5e MM, the only dire creature is a dire wolf, which makes reverse engineering easy:
- CR +2 (1/4 to 1)
- Speed +10
- hp: 2d8+2 to 5d10+10 —+3 HD and the HD go up a category.
- Size +1
AC +1 —not +5 natural armour, which makes sense in light of the AC+proficiency changes
- Str +5 —not +8
- Dex +0 —not +2
- Con +3 —not +8
- The mental stats are unchanged. Except for Cha +1 which may be a typo.
- +4 to +5 to hit (+2 proficiency, switch from finesse to strength, no focus). damage dice increase.