In the inner pot of Instant Pot, pour 4 cups of the chicken stock. Add the carrots, celery, onion, meatballs and pasta.
Place and lock lid. Set valve to SEAL and program pot on MANUAL, high pressure for 8 minutes.
When the timer elapses, carefully quick release pressure and remove lid.
Stir in the remaining 4 cups chicken stock and wilt in the baby spinach, turning pot to SAUTE if more heat is necessary.
Ladle into bowls and serve.