Is Assert Authority legal in Standard, Modern, and Commander?

Assert Authority is legal in: Modern, Legacy, Vintage, Commander.

Assert Authority

Q: What type of card is Assert Authority?

Assert Authority is an Instant. Its oracle text reads: "Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.) Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."