Authenticity of the Hadith
Other than Tirmidhi, Ibne Maja  gives three independent narrations of the same hadith. Talking about the authenticity of this hadith Abu Mansur Abd al-Kahir ibn-Tahir Al-Baghdadi  says:
"There are many isnad (independent testimonies) for the tradition dealing with the division of the community. A number of following companions have handed it down as coming from the Prophet (peace be upon him): Anas ibn-Malik, Abu-Hurairah, Abu-l-Darda, Jabir, Abu-Sa'id al-Khidri, Ubai ibn-Ka'b, Abd-Allah ibn-Amr ibn-al-'As, abu-Imamah, Wathilah ibn-al-Aska' and others. It is also handed down that the pious Caliphs mentioned that the community would be divided after them, that one sect only would save itself, and the rest of them would be given to error in this world, and to destruction in the next."
So it becomes quite clear that there is no doubt about the authenticity of this hadith and great scholars of Islam like al-Baghdadi regarded this hadith to be an authentic one. While talking about the types of divisions to occur among the Muslim Ummah, Abu-Mansur al-Baghdadi  says:
"Every man of intelligence among the authors of the treatise has known that the Prophet (peace be upon him) in speaking of the divisions that were to be condemned and the members of which were destined for hell-fire, did not mean the various legal schools, who, though they disagreed as to the derivative Institutes of Law, agreed concerning the fundamentals of religion.......... And verily the Prophet (peace be upon him), in mentioning the sects condemned, had in mind only those holders of erring opinions who differ from the one sect which will be saved, in such matters as ethics and the unity, promises and threats (regarding future life), predestination and free-will, the determination of good and evil, right guidance and error, the Will and Wish of God, prophetic vision and understanding, the attributes of Allah, His Names and Qualities, any question concerning what is ordered and what is permitted, [signs for] prophecy and its conditions, and similar questions."