Yes.

Hi, I realise this is an old issue but I'd like some further clarification.

The distinction between a Subscriber and an Observer is that Subscribers are part of the Reactive Stream specification, where the first rule of Subscribers is that they must "MUST signal demand via Subscription.request(long n) to receive onNext signals."

Since Observables don't have backpressure support, and therefore don't signal demand via request(long n), they use Observer, which doesn't have the request method.

Am I on the right track?

Since Observables don't have backpressure support, there is no need for a Subscription with a request() method. To avoid some confusion, separate "connection" types is employed: Disposable with a dispose() method that is analogous to Subscription.cancel().