what is the hyphotesis in computer science research(especifically AI research)?
AI is a very applied domain, so from a big picture point of view the problem is often defined by a real world application. For example, machine translation fills a need for low cost translation (so this particular need is the problem). In this general setting, an hypothesis is for instance: "the machine can produce good quality translation", and researchers try to prove it.

However it's more common for a paper to motivate the work at a more fine-grained level using the existing body of literature. For example many approaches have been studied for machine translation, with varying levels of performance and flaws. A researcher in this field might want to study a specific question, e.g. "how to improve translation of multiword expressions from language A to language B" and formulate an hypothesis such as: "recent approach X can improve translation of multiword expressions from language A to language B". Here the problem is formulated as the need to improve over the current state of the art, implicitly assuming that the underlying problem (machine translation in general) is sufficiently established.