The theological claim that the scripture simply is the Guru rests on a specific and traceable compilation history, showing the claim was not asserted about just any collection of devotional poetry but a text assembled with unusual editorial care over more than a century.
Guru Arjan, the fifth Guru, compiled the first authoritative recension, the Adi Granth, completing it in 1604 and installing it at the Harmandir Sahib (the Golden Temple) at Amritsar, drawing together the compositions of his four predecessor Gurus, his own hymns, and the works of the bhagats, the Hindu and Muslim saints noted elsewhere, into a single volume arranged by musical mode. The compilation was partly a response to spurious hymns falsely attributed to the Gurus by rival claimants to leadership, so establishing an authoritative text served a practical function of guarding the tradition against forgery as much as a devotional one.
Guru Gobind Singh, the tenth Guru, added the hymns of his father, Guru Tegh Bahadur, producing the version now recognized as final, and shortly before his death in 1708 declared that the line of personal Gurus was ending and that the scripture itself, now titled the Guru Granth Sahib, would be the eternal Guru thereafter, a declaration Sikhs mark annually as the founding act of the tradition's current religious authority. The text has since been fixed at a standard 1,430 pages in modern editions, with standardized pagination used worldwide so a citation means the same thing wherever printed, extending the same concern for textual integrity that motivated Guru Arjan's original compilation.