is there anything bigger then prime, alpha death claw or a super mutant behemoth or even tales of large creatures possibly an escaped experiment on gene splicing or a chimera

What?

Prime is the biggest Robot seen in Fallout. Legendary Deathclaw I believe is bigger than the Alpha Male and Super Mutant Behemoths are as big as they get.

I am sure Bethesda might think of something bigger for the next game.

That robot from tactics was pretty [censored] huge, just the top of my head...maybe a mutated whale if they exsist

Behemoth Robots are big, but not bigger than Prime.

I'm prepared to have no such type of giants in the game. Unless it's wild elephants that escaped from a zoo.