What is the Indo-Hittite hypothesis about the relationship between Anatolian and other Indo-European languages?

The Indo-Hittite hypothesis is a theory proposing that the Anatolian languages—such as Hittite—and the other Indo-European languages share a common ancestor, but that they diverged from one another before the other Indo-European branches (like Celtic or Germanic) developed.1

Under this hypothesis, scholars suggest that a primitive "Indo-Hittite" protolanguage split into two distinct branches: one becoming the Anatolian languages and the other becoming the ancestor of all other Indo-European languages. This contrasts with the more common view that Anatolian is simply one branch among many within the Indo-European family tree.1

It is important to note that there is no scholarly consensus on this issue. Many researchers continue to classify Anatolian as a standard branch of Indo-European, and extreme versions of either hypothesis are widely considered unlikely to be entirely correct. As of the early 21st century, the exact nature of the relationship remains a subject of ongoing academic debate.1