Is Siphon Insight legal in Standard, Modern, and Commander?

Siphon Insight is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Historic.

Siphon Insight

Q: What type of card is Siphon Insight?

Siphon Insight is an Instant. Its oracle text reads: "Look at the top two cards of target opponent's library. Exile one of them face down and put the other on the bottom of that library. You may play the exiled card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell. Flashback {1}{U}{B}"

Instant

Look at the top two cards of target opponent's library. Exile one of them face down and put the other on the bottom of that library. You may play the exiled card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell.

Flashback