I don't believe the APIs are actually under marginal cost. Inference is cheap, but people are using a lot of it.

The problem is, the arguments you're making could be used for almost any industry, including ones that we've seen sustained excess profits.

It depends on how you define sustained and define excess profits.

Being an unusually effective and well managed company can certainly yield sustained above average returns but that hardly means that is a meaningful barrier to entry - the question at hand.

Ozempic is marked up 200x (20,000%) because they're able to extract monopolistic rents, that's a completely different ballpark of 2x or even 5x markups.

In a fully commoditized industry participants yield average ROIs, in a mature market it's industry dependent but I would consider ranges from 10% to 100% above average ROIs to be reasonably normal. It's when things get to 10x to > 100x that I would consider to be able to extract monopolistic rents. I know I'm mixing up profits (ROIs) with markups on COGs with the issue being that companies extracting monopolistic rents tend to obscure the fact with padded expenses and the financial details needed to calculate Total Production Cost per Unit are generally not available.