[WorldMaker]

I've also argued against /api for similar reasons under "strict REST", too. It's often "redundant" information not all that useful in the URL hierarchy. Everything is an API. There's no "non-API" endpoints. Even pages that only return HTML are a public API. But I also understand the usefulness for things like security audits to have a magic circle labeled /api even though that magic circle doesn't really do anything.

I think you are almost assuming the implementer doesn't abstract the URL routing in some way and has to care about about every possible URL route? In practice there is often very little difference on the implementer side between routing `/api/v{id}/some/route` and pulling in the version number as a route parameter and picking up a version number from a header. The implementer is still just seeing a version number parameter injected either from their routing framework or their header dictionary. In both cases the amount of code they see is roughly the same. In many cases all "versions" of the code might only be a single "Controller". Outside of a few languages such as PHP there's few languages that have a direct 1:1 between URL paths and "Controllers" or "Source Files" or anything resembling that. At some point there's always some intuition that side-by-side versions imply side-by-side code and the "tech debt" sense of that maintenance version, but that intuition comes from numbers of classes and size of classes and indirect measurements like PR cycle time and Sprint planning estimates, and is never directly connected to URL routing versus Header negotiation. (Again, in modern languages with modern routing frameworks. Obviously if you have to drop a PHP or ColdFusion file for every API endpoint you'll feel URLs a lot more painfully than that.)