Most applications I’m building today are using a kind of Web API. This works great, but leads to chatty interfaces, requiring a large number of requests to get all the required data. In situations where the API is only for internal usage and you don’t want to share it with other applications, your application can benefit from a technique called ‘Request Batching’.
Remark: Be aware that Batch requests are not REST-compliant. So if you are creating a public API stop reading… 
What is it?
Request batching combines multiple API requests into a single POST request. HTTP provides this out-of-the-box using a special content type called Multipart. On server-side, requests are unpacked and dispatched to the appropriate API methods. All responses are packed together and sent back to the client as a single HTTP response. The nice thing is that it is already supported by ASP.NET web API and you don’t need a lot of extra code to get it working.
Enable Request Batching in ASP.NET Web API
The only thing you need to do to get it working inside ASP.NET Web API is defining an extra route:
Inside the route you can use the DefaultHttpBatchHandler or create your own custom implementation:
In the above sample I changed the ExecutionOrder property. By setting this to non-sequential, API requests are executed in parallel.
From the client, you can consume this Batch API like this: