API versioning is often indicated by the letter “v” followed by a number, e.g. “v3”. For a REST-based API, the version is usually found in the URI, e.g. “https://api.example.com/v3/users”.
Interestingly, HubSpot, which follows an API-first approach, is abandoning this type of versioning. With their current version 2026-03, they are now using date-based versioning and have explained this decision in a blog post.
An interesting move, in my opinion. An API version is supported for 18 months. Whether you’re using a supported API version is now quickly apparent from the URI. I find that very convenient.