Private feedback is the part of a client's end-of-contract review that Upwork collects but never shows on the profile, chiefly whether the client would recommend the freelancer or agency, and it feeds the Job Success Score.
When a contract ends, both sides fill in a feedback form. Part of it is public: the star rating and the written comment that appear on the work history. Part of it is private: the client is asked how likely they would be to recommend the freelancer or agency, and the freelancer is asked a similar question about the client along with the reason the contract ended. Upwork's Help Center states that private answers are never shown to the other party and are not published anywhere.
The private answer matters because Upwork feeds it into the Job Success Score. A client who leaves five stars in public and a lukewarm private answer can lower the score, which is the usual explanation when a freelancer sees the JSS fall after a contract that looked successful. Upwork does not say how heavily it weighs the private answer against the public one, only that both count.
Two misunderstandings are common. Private feedback is not the "reason for ending the contract" menu alone; it is the whole hidden section of the form. And it cannot be seen, disputed or answered, so the only remedies are the Top Rated feedback removal perk and asking the client, before the contract closes, whether anything was wrong.
How Upwork Insights uses it
This term describes Upwork's own rules or product rather than a figure the index measures; the pages that do carry live figures are the stats and rate pages.