Is Clockwork Steed legal in Standard, Modern, and Commander?

Clockwork Steed is legal in: Legacy, Vintage, Commander, Pauper.

Clockwork Steed

Q: What type of card is Clockwork Steed?

Clockwork Steed is an Artifact Creature — Horse. Its oracle text reads: "Clockwork Steed enters with four +1/+0 counters on it.Clockwork Steed can't be blocked by artifact creatures.At end of combat, if Clockwork Steed attacked or blocked this combat, remove a +1/+0 counter from it.{X}, {T}: Put up to X +1/+0 counters on Clockwork Steed. This ability can't cause the total number of +1/+0 counters on Clockwork Steed to be greater than four. Activate only during your upkeep."

Artifact Creature — Horse

Clockwork Steed enters with four +1/+0 counters on it.<br>Clockwork Steed can't be blocked by artifact creatures.<br>At end of combat, if Clockwork Steed attacked or blocked this combat, remove a +1/+0 counter from it.<br>, : Put up to X +1/+0 counters on Clockwork Steed. This ability can't cause the total number of +1/+0 counters on Clockwork Steed to be greater than four. Activate only during your upkeep.