Does Virtuoso's ability trigger when a 4-cost spell gets countered?

Ruling: No, Virtuoso's ability will not trigger if the spell is countered. A countered card is not considered to have been played, so "When you play a spell" triggers do not activate.

Sequence:

• You play a spell and place it on the chain
• Opponent counters the spell
• The spell is removed from the chain before resolving
• Because the spell never resolves, it is not considered "played"
• Virtuoso's "When you play a spell" ability does not trigger

Nuances:

• There is a distinction between "When you play a spell" triggers (which require the spell to resolve) and "When you choose/target" triggers (which occur when the spell is finalized on the chain, before potential counters)
• "When you choose/target" abilities would still trigger even if the spell is later countered, because the targeting action was already completed