These are APIs.json blueprints for some of the leading API producers out there, taking the APIs.json for their API operations and distilling it down into a blueprint you can following when crafting your own operational definition.
Amazon Web Services - Amazon is one of the early API pioneers and their often formulaic approach provides an interesting blueprint for how API providers can approach their operations. Many of the AWS API operations are consistent, but there are also individual APIs that take their own approach and clearly disagree with the common approach provided. This blueprint is probably one of the more sophisticated for one of the largest providers available in the API realm.
eBay - eBay is another API provider and has yet another approach to their operations that they have crafted over the last quarter century. This is a blueprint of their API operations showcasing the individual properties for their APIs as well as the common ones. eBay is a medium-sized API provider and offers a unique view of how to operate your APIs with fewer essential API properties across multiple types of APIs that power commerce applications.
Stripe - Stripe is often held up as a model for the entire API space, demonstrating not just quality APIs, but high quality API operations. Stripe's approach to developing, iterating, and supporting their APIs holds lots of lessons for API providers and provides an excellent blueprint.
Twilio - Twilio has long been the reigning champion for how you should deliver and support your APIs. Developers have long loved them for how they operate their platform, making them a perfect candidate for how you should be doing APIs, offering one of the leading APIs.json blueprint that other API providers can follow.