Definition of "breakneck"

The line to Dunières conists of a series of breakneck descents almost invariably ended by a violent curve and followed immediately by a panting climb, on which the engine barked thunderously but failed unhappily to maintain its booked speed of 13 m.p.h.

1961 November, H. G. Ellison, P. G. Barlow, “Journey through France: Part One”, in Trains Illustrated, page 668

The use of machine learning in this field is hardly new, but the breakneck pace at which it is improving is worrying, Lund says: “With the advent of ChatGPT, the future is bleak.”

2023 June 27, Clea Skopeliti, “‘The future is bleak’: how AI concerns are shaping graduate’s career choices”, in The Guardian‎