Lord Krishna Himself gives the answer in the Bhagavad Gita

The Bhagavad Gita, located within the Mahabharata's Bhisma-parvan, comprises chapters 23 to 40 in its original manuscript form. It is frequently studied as an independent text, renumbered into 18 chapters, and exists in a variety of Indic scripts, including both modern and ancient forms. Despite numerous variants across the Mahabharata, Gita manuscripts maintain consistent meanings with only minor differences. Scholars suggest the text originally contained around 745 verses, with 700 being the accepted standard, detailing dialogues among key characters like Krishna and Arjuna.