** Shares of IT research firm Gartner IT.N plunge about 20% in premarket trading

** Sees 2026 total revenue of $6.46 bln, below analysts' average expectations of $6.71 bln, according to data compiled by LSEG

** Expects annual adjusted earnings of $12.30 per share, below expectations of $13.53

** Projects annual revenue of $5.19 bln at the insights unit, its biggest, below estimates of $5.3 bln

** For Q4, co reports quarterly revenue of $1.75 bln, in line with analyst estimates

** Adj earnings of $3.94 per share beats estimates of $3.51 per share

** Reports a 13% fall in Q4 revenue at its consulting segment from a year ago

** Up to last close, IT had fallen 19.8% YTD

(Reporting by Arnav Mishra in Bengaluru)

((Arnav.Mishra@thomsonreuters.com;))