Trim the stem ends from the Brussels sprouts and halve them through the root. Discard yellowed outer leaves.
Toss the halved sprouts with olive oil, kosher salt, and black pepper until evenly coated.
Arrange in a single layer in the air fryer basket, cut side down. Air fry at 380°F for 12 to 14 minutes, shaking the basket halfway through, until deeply browned and tender.
While the sprouts cook, combine the balsamic vinegar and honey in a small saucepan over medium-low heat. Simmer about 4 minutes, stirring constantly, until thickened enough to coat a spoon. Watch closely — honey burns quickly.
Transfer the hot sprouts to a bowl, pour the glaze over, and toss to coat.
Optional: return the glazed sprouts to the basket for 1 to 2 minutes at 380°F for extra caramelization. Do not exceed 2 minutes.
Serve immediately.