It's basically depending on how you reference your WIG project in your main project. Based on what you described above, you have used a project reference. In that scenario, you are indeed seeing the .Definition namespace of the WIG project, but if you reference the dll directly, you will get correct IntelliSense. Note, that the project reference works during the build time as well, it's just IntelliSense having an issue with it.

As a workaround if you are developing in Visual Studio you can turn off the following setting to get the project reference working:

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Tools -> Options -> Text Editor -> F# -> Performance -> Enable in-memory cross project references