Is there a HN API to extract upvoted stories and comments?

Are you asking about stories/comments upvoted by you ? In that case, your profile on HN has a link for the 2 already at the bottom. I noticed this recently so may be a new addition.

https://news.ycombinator.com/upvoted?id=gautamsomani (only you can see this btw)

https://news.ycombinator.com/upvoted?id=gautamsomani&comment...

Google BigQuery has the full database, updated daily.

Check out the links at the bottom of every page.