The Gita is often referred to as an upanishhad, and according to some it contains the truth of all of them.The fundamental thoughts of the upanishads, the conclusions and theories are expounded in the Gita. The Gita has been given the status of a Upanishad as enunciated in the following verse:
sarvopanishhado gaavo dogdhaa gopaalanandanaH
paartho vatsaH sudhiirbhoktaa dugdhaM giitaamR^itaM mahat.h
This means that all the upanishads are the cows and Lord Krishna, the son of a cowherd, is the milker. Arjuna is the calf, all the pure minded people are the consumers and the ambrosial Gita is the delicious milk.