You do not control the trigger, it will activate any time a spell is cast with a cmc equal to the number of counters at the time the spell is cast.
While the answer is correct, the word choice is less than optimal. You do indeed control the triggered ability of a Chalice that you control, and that ability will trigger, not activate, whenever a spell with the appropriate CMC is cast.
Of course, as pointed out, there is no choice involved here; if Chalice of the Void's triggered ability is triggered, it will counter the spell when its triggered ability resolves.
URStormRU
GRTitanshift[mana]RG/mana]
― Anthony Bourdain, Kitchen Confidential
I will always firmly stand by the belief that Magic is a game first and a collectable second.
While the answer is correct, the word choice is less than optimal. You do indeed control the triggered ability of a Chalice that you control, and that ability will trigger, not activate, whenever a spell with the appropriate CMC is cast.
Of course, as pointed out, there is no choice involved here; if Chalice of the Void's triggered ability is triggered, it will counter the spell when its triggered ability resolves.
Commander/EDH Decks:
BRG The Blood of Jund - Kresh the Bloodbraided BRG
WR The Blades of Goldnight - Gisela, Blade of Goldnight WR