Historical Rules · 22 April 2021
Rule 702.44a
Official source text from the 22 April 2021 Rules release
Sunburst is a static ability that functions as an object is entering the battlefield. “Sunburst” means “If this object is entering the battlefield as a creature, ignoring any type-changing effects that would affect it, it enters the battlefield with a +1/+1 counter on it for each color of mana spent to cast it. Otherwise, it enters the battlefield with a charge counter on it for each color of mana spent to cast it.”