I am in Spiti right now…hope you are going with a good driver otherwise you’re gonna stuck. Make sure your car or traveller has chains. Keep some food in stock and plenty of water. It’s -25 rn so expect it to be same or worse in Tabo or Kaza.
Also, your tour advisor may advise you to take Diamox but don’t. It’s not needed if your water intake is good (>2.5 L). These Delhi group tours advisors are shit. I would say if you have time then go with a local tour group.they might be expensive but a local himacahli would be travelling with you and telling you all about the monastery or place or valley, also they would be better in judging conditions and taking a quick call. Have seen many Delhi based tour groups stuck in Nako or Gue due to snow. My group didn’t 😅