By the grace of Vyasa, I heard this supreme and most secret Yoga directly from Krishna himself — the master of all yoga — as he himself declared it.

Sanjaya names his own source of grace: it was Vyasa who gave him the divine vision through which he could hear and see everything on the battlefield as if present. And what he heard was not a second-hand report but the living teaching: sākṣāt kathayataḥ svayam — declared directly, by the Lord himself, in person. The chain of transmission is complete: Lord to Arjuna on the battlefield, Arjuna to all seekers through the text, Sanjaya to Dhritarashtra across the distance, Vyasa to all ages through the Mahabharata. Every link in the chain is an act of grace.