[t0k0l0sh]

That policy covers in-game content too - the same page mentions:

"Steam does not contain any paid advertising, nor are advertising models supported in games distributed on Steam. There are varying interpretations for what constitutes ‘advertising’ in a game, so the examples below are meant to help guide developers as to what is and is not supported on Steam."

Under not supported: "Developers should not utilize paid advertising as a business model in their game"

The Borderlands 4 adverts in BL3 are not paid adverts, and they don't advertise anything other than their own games.

[jrootabega]

Yep, the page does, but the specific section you named, suggesting it was an answer, does not. At least it does not alone address the issue.

But leaving that section aside, I'll say that these ads are paid. They're paid by the company to itself, with the intent of future monetary gain. Now, if you think that's too much of a technicality, which I would understand, I'll say this: would it be a violation of the policy to show unskippable first-party advertisements repeatedly during gameplay? I think most people would agree that it would be a violation of the intention of the policy.

[t0k0l0sh]

I don't think the specific section needs to mention it - the entire page is about Advertising on Steam, which according to the opening paragraph, includes in-game adverts. The rest of the page elaborates with examples of things they do and don't condone.

These ads are indeed paid for by the company itself, but seem to be permitted by the policy. The intent/spirit of the policy seems to be to prevent games showing ads for arbitrary other games/things, for example BL3 showing ads for Candy Crush Saga - this isn't allowed by this policy, i.e. games that are paid to show other people's ads.

Gearbox showing BL4 ads in BL3 etc, it seems to count as cross promotion, they're not being paid for the act of showing the ad and is OK according to Steam - "These types of promotions are encouraged and many customers find value in them."

Perhaps the wording of the policy could use some work to make things clearer.