I am impressed with the work that the Open API Initiative (OAI) working group has accomplished with the Version 3.0 release of the OpenAPI Specification. I have had zero involvement in moving the specification forward (something I'm changing), and after coming back to the effort, I am impressed with what they've prioritized and accomplished for this release. 

The highlights in Version 3.0 of the OpenAPI Spec for me are:

• Components. The new components architecture really reflects APIs in my opinion, making things modular and reusable.
• Body. They're catching up when it comes to allowing the body to be defined separately from the headers and parameters.
• Content negotiation. You can now define content objects to define the relationship between response objects, media types, and schema.
• Linking. It isn't hypermedia, but it is definitely a nod towards hypermedia, allowing the linking of objects.
• Webhooks. You can now define callbacks that can be attached to a subscription operation describing an outbound operation.
• Schema. Increased investment in JSON schema, including support of oneOf, anyOf, and not support, as well allowing for alternative schema now.
• Hosts. You can now have multiple hosts, allowing you to more narrowly define the host for each path.
• Examples. Allows you to better describe and provide examples of APIs responses and requests.
• Version identifier. Not a big one, but removing the "Swagger: 2.0" identifier; it will now just be OpenAPI.
• Cookies. I'm not a big fan of this being introduced, but it makes sense, and I'm sure is usable for many API operators.

The OAI blog provides a five-part series covering the version 3.0 release. These ten areas are the highlights for me. I think they nailed it as far as what was needed while also pushing into areas like linking and webhooks that I hadn't anticipated. I am looking forward to playing with converting some of my 2.0 specs to be 3.0-compliant. Once I am a little more intimate with it, I can do better to estimate how long it will take for me to evolve my platform from 2.0 to 3.0.

I am impressed with what the OpenAPI Spec working group has gotten accomplished. I am optimistic about what is possible with OpenAPI Spec in 2017 — something I'm going to be investing in heavily.