What Version of OData is supported by DataDirect Cloud?

Actually, neither.  D2C supports OData version 2.  This is documented here

documentation.progress.com/.../index.html

The OData service library used by D2C only supports version 2.  There were no viable libraries available that supported version 3 or 4 at the time we started the OData work.

I did find out how to check this myself.   The OData specification states that the version should appear in the $metadata as a DataServiceVersion attribute.

If you ask D2C for the OData $metadata  (e.g https://service.datadirectcloud.com/api/odata/ExampleDataSource/$metadata) then you will see the tag as follows (note that you need to scroll the 2nd line to the right as the m:DataServiceVersion is at the end of the line.):

<edmx:Edmx xmlns:edmx="http://schemas.microsoft.com/ado/2007/06/edmx" Version="1.0">
  <edmx:DataServices xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata" m:DataServiceVersion="2.0">
     <Schema xmlns="http://schemas.microsoft.com/ado/2008/09/edm" Namespace="ExampleDataSource">

According to the OData Rules posted at http://services.odata.org/validation/roadmap.htm#rules, the following is stated:

 DataServiceVersion attribute MUST be in the data service metadata namespace and SHOULD be present on a <edmx:DataServices> element ....