Do innate spells follow concentration rules?

[Segev]

For instance, a gray slaad has both invisibility and fly as innate spells. Can it have both up, or must it choose, like any normal spellcaster?

[Anymage]

Once a gray slaad starts casting a spell, the only way it's different from a sorcerer doing so is that the slaad doesn't need material components. It doesn't say anything about being able to sidestep concentration. And given how much of a factor concentration is in this edition, I wouldn't expect innate spellcasting to ignore it without very blatantly spelling that out.

[Amnestic]

Unless otherwise specified in the spellcasting entry, they follow all the standard rules. In the Grey Slaad's case, they don't require material components but that's it. It would still require concentration.

MM page 10 has the entries for monster spellcasting stuff.

[Unoriginal]

For instance, a gray slaad has both invisibility and fly as innate spells. Can it have both up, or must it choose, like any normal spellcaster?

Yes, Concentration does apply normally. It's only different in the ways the monster statblock precises.

[Segev]

That’s what I thought. Thanks for confirming for me.