Sarek's cruiser was a Vulcan cruiser owned by Sarek operating under a diplomatic registry number.
In 2256, this cruiser was to ferry Sarek to a secret meeting with the Klingons on Cancri IV. However, the ship was disabled and stranded inside the Yridia Nebula by V'Latak's sabotage. (DIS: "Lethe")
In 2257, Amanda Grayson took the ship to Starbase 5 to find out what had happened to Spock. After the doctors there refused to reveal any information, Amanda stole Spock's medical file and sought out the USS Discovery, approaching without identifying themselves and using a diplomatic frequency. (DIS: "Point of Light")
After sensing Michael Burnham was in danger through their katric connection, Sarek and Amanda tracked down the Discovery aboard Sarek's cruiser to say their goodbyes. They departed aboard the cruiser shortly before the Battle near Xahea. (DIS: "Such Sweet Sorrow")