Is Gears of War 4 on Steam?

No. Gears of War 4 is not distributed on Steam, so there is no Steam Charts or SteamDB player count for it. Its live popularity is tracked here via Twitch viewership instead.

What platforms is Gears of War 4 on?

Gears of War 4 is available on PC (Microsoft Windows), Xbox One.

When did Gears of War 4 release?

Gears of War 4 was first released on October 11, 2016.

Gears of War 4

Oct 11, 2016ShooterPC (Microsoft Windows)Xbox One

Gears of War 4 — frequently asked questions

Is Gears of War 4 on Steam?: No. Gears of War 4 is not distributed on Steam, so there is no Steam Charts or SteamDB player count for it. Its live popularity is tracked here via Twitch viewership instead.
What platforms is Gears of War 4 on?: Gears of War 4 is available on PC (Microsoft Windows), Xbox One.
When did Gears of War 4 release?: Gears of War 4 was first released on October 11, 2016.

About Gears of War 4

A new saga begins for one of the most acclaimed video game franchises in history. After narrowly escaping an attack on their village, JD Fenix and his friends, Kait and Del, must rescue the ones they love and discover the source of a monstrous new enemy.

Summary via IGDB.

Gears of War 4 on Wikipedia

Gears of War 4 is a 2016 third-person shooter game developed by The Coalition and published by Microsoft Studios for Windows and Xbox One. It is the fourth main installment in the Gears of War series, and the first mainline entry not to be developed by Epic Games. Taking place 25 years after the events of Gears of War 3, the game's plot, which can be played in single or co-operative play, focuses on James Dominic "JD" Fenix, son of Marcus Fenix, as he and his allies take on the Swarm, a new threat related to the Locusts.

Source: Wikipedia (text under CC BY-SA 4.0).