In new documentation, Valve has clarified a policy that prohibits games released on Steam from including mandatory in-game ads that players must watch or engage with.
A newSteamworks Documentationpage has raised awareness about a certain Valve policy concerning advertising onSteam.

The documentation further states if a game’s model relies on advertising on other platforms, developers must “remove those elements before shipping on Steam.”
Valve banning games with forced ads on Steam isn’t new
Long-time Steam users in thegaming subredditnote that Valve has had this policy in place for several years. Thus, it appears the company is merely clarifying its stance by creating a dedicated page in the Steamworks Documentation used for partners.
“It was actually policy for a few years. It’s just been more explicit now…” one person explained in the aforementioned Reddit thread.

As another user noted, details about the mandatory in-game ad ban were previously present in thedocument’s “Pricing” sectionand attached to an FAQ blurb concerning whether or not “Steam pricing support[s] games with paid ads.”
In terms of what Steam’s policy does allow, players will find games on the storefront that feature product placement for real brands. So a racing game advertising, say, Red Bull energy drinks on an in-game billboard falls in line with Valve’s stated guidelines.

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Problems would only arise in this situation if players had to watch an energy drink commercial to race on certain tracks.