In Indo-European linguistics, the term Indo-Hittite (also Indo-Anatolian) refers to the hypothesis that the Anatolian languages may have split off the Proto-Indo-European language considerably earlier than the separation of the remaining Indo-European languages. The term is somewhat imprecise, as the prefix Indo- does not refer to the Indo-Aryan branch in particular, but is iconic for Indo-European, and the -Hittite part refers to the Anatolian language family as a whole.
It is generally accepted that the Anatolian branch was separated earlier, but while mainstream Indo-European linguistics holds that this may have been a matter of a couple of centuries, maybe roughly 4000 BC in the Kurgan framework, proponents of the Indo-Hittite hypothesis claim the separation may have preceded the spread of the remaining branches by several millennia, possibly as early as 7000 BC. In this context, the proto-language before the split of Anatolian would be called Proto-Indo-Hittite, and the proto-language of the remaining branches, before the next split, presumably of Tocharian, would be called Proto-Indo-European(PIE). This is a matter of terminology, though, as the hypothesis does not dispute the ultimate genetic relation of Anatolian with Indo-European, it just means to emphasize the assumed magnitude of temporal separation.
A crucial question is, thus, whether the Anatolian branch split off before the beginning of the Bronze Age, or even the Chalcolithic. A Bronze Age society is usually reconstructed from PIE vocabulary, but it is unclear whether this necessarily holds for inherited vocabulary in Anatolian. The Bronze Age begins roughly 3300 BC in the Caucasus, precisely the area that separates the historical Anatolian speakers from the remaining branches; it is therefore possible that the Proto-Anatolians themselves were involved with the earliest development of Bronze metallurgy. In any case, while evidence that Anatolian shares common terminology of metallurgy with other branches would speak against Indo-Hittite, the opposite case does not imply evidence in favour of Indo-Hittite, since even a 'moderate Indo-Hittite' split around 4000 BC would clearly predate the Bronze Age.