Is Kate Stewart legal in Standard, Modern, and Commander?

Kate Stewart is legal in: Legacy, Vintage, Commander.

Kate Stewart

Q: What type of card is Kate Stewart?

Kate Stewart is a Legendary Creature — Human Scientist. Its oracle text reads: "Whenever you put one or more time counters on a permanent you control, create a 1/1 white Soldier creature token. Whenever Kate Stewart attacks, you may pay {8}. If you do, attacking creatures get +X/+X until end of turn, where X is the number of time counters among permanents you control."

Legendary Creature — Human Scientist

Whenever you put one or more time counters on a permanent you control, create a 1/1 white Soldier creature token.

Whenever Kate Stewart attacks, you may pay . If you do, attacking creatures get +X/+X until end of turn, where X is the number of time counters among permanents you control.