Pour cider into a 4- or 5-quart slow cooker; add orange rounds.

Tie cinnamon, cloves, allspice, and star anise in double-layer cheesecloth; add to cider.

Stir in maple syrup. Cover; cook on low for 1 1/2 to 2 hours until fragrant and steaming, not boiling.

Remove spice bundle and orange rounds before they turn cider bitter.

Stir in vanilla; switch to warm for up to 3 hours.

Ladle into mugs, keeping heat low enough to prevent bubbling.