FM4 on Gamepass

Unlikely. The problem with games like Forza is the licence to use the cars runs out after a certain time which is why the older Forza games get delisted. As it is they wouldn't be allowed to put Forza 4 on gamepass.

As Daft Badger explained above, previous Forza titles are delisted from the Microsoft/Xbox store, due to expired licensing for the cars and music in the games. The DLCs, add-ons, and the game itself are unavailable and would never be added to Game Pass for this reason.

Currently, the only Forza titles available to purchase on the Microsoft/Xbox store are FM7 and FH4. Forza Street is available on the Microsoft store for compatible devices (PC, Android, and iOS, but not on Xbox consoles, unfortunately). FM7 and FH4 are free to play on Game Pass.

Of course, you can still purchase FM4 on disc though. There are some pre-owned copies for around £5 (or local currency equivalent) on online retailers such as Amazon

Also, Forza Motorsport 4 is not backwards compatible anyway. The game is only available on Xbox 360, and Game Pass is only available on PC (Windows 10), Xbox One, and Series X|S.

[FM4] Massive Crash - [View:http://www.youtube.com/watch?v=MTzT0C6x_Uo]

[FM4] Ferrari Flip - [View:http://www.youtube.com/watch?v=uhPxsPprR64]

[FM4] Trueno Flip - [View:http://www.youtube.com/watch?v=bqHEOisQ_to]

I spent over $150 on FM4 (DLC totaled over 8000 MS points). I spent double that on going to the movies in the last year. Fifty hours at the movies vs hundreds of hours playing FM4, and I enjoyed my time with FM4 more. The math is there. I'll do it again
with Horizon. That's how these $110 games sell.

Here's the thing for me... Since GT5 released before FM4, I had it first. I've been playing GT since the first one, as I have FM (I'm basically a sim racing fan). When I first started playing FM4, it just didn't feel as smooth or as real as GT5. After I
played FM4 to death, I went back to GT5. When I did that, GT5 didn't immediately feel greatly superior, but it (the actual on-track racing part) also didn't feel as sloppy as FM4. After a while I got back on FM4. Unlike when I restarted GT5, FM4 immediately
felt grossly inferior as far as the actual racing goes. In GT5, the AI actually races. It anticipates, utilizes the track & opportunities properly and it recognizes & reacts to other vehicles (AI & player) in ways that make FM4's AI seem almost retarded in
comparison. When watching replays of races in GT5 & FM4... GT5's play out like real automobile racing would. There's none of the destruction derby, inappropriate braking or seemingly intoxicated swerving & jerky maneuvers that are the norm in FM4. Compare
the hired AI drivers (called B-Spec mode in GT5) and you'll see just how bad FM4's AI really is. FM4's AI drivers barely know how to drive a car, let alone race one in comparison. GT5's drivers have a racing instinct, where FM4's seem to just plow their way
into the programmed line they're supposed to be running, regardless of traffic, track or anything else. Looking at both games, it seems as though FM4's developers concentrated on presentation, customization & things like that. Playing GT5, it would seem it's
development team was more concerned with the actual racing aspects & getting them right, because as far as that goes, the two games are like night & day.