Assuming that Stripe's userbase grows over time and that their new API versions offer features that are useful to a significant portion of their existing userbase, I would expect the majority of requests at any time to be for a recent API version that needs few (or no) transformations. This is especially likely considering that Stripe provides official client libraries (which are presumably up to date) for a lot of languages.
Stripe probably tracks the relative usage of each API version. If they found a lot of their users were stuck on an old version, that would point to a bigger problem than just some per-request overhead.
Stripe probably tracks the relative usage of each API version. If they found a lot of their users were stuck on an old version, that would point to a bigger problem than just some per-request overhead.
I'm not sure how true that is. In my experience, integrations with online payment services are mostly write-only code: you do it, you test it, and then no-one goes near it once it's in production unless there's some sort of known bug or security issue.
Literally the last thing I want to do with working, tested code integrating with the service that collects money for a business is make unnecessary changes that might break it. I know several businesses that use versions of APIs that are several years old with services like Stripe, because they have no need to change.
Stripe probably tracks the relative usage of each API version. If they found a lot of their users were stuck on an old version, that would point to a bigger problem than just some per-request overhead.