Ember Octane when calling a save on the model what is the default accept and content-type headers?

In Ember Octane, when calling a save on the model, which calls a save to the back-end (.NET CORE 3.1), what is the default accept and content-type headers? I have tried looking online, but I cannot seem to find anything in the documentation.

Is it application/json or application/vnd.api+json?