According to Philip Baker Hall, Philip Seymour Hoffman improvised his scenes, including most of the craps scene.
Paul Thomas Anderson's original title for this film was "Sydney". Since it was his first film, and he had basically no control over it (much less final cut, like he's had on his other features since), Rysher Entertainment re-cut the film and retitled it "Hard Eight". This enraged Anderson, and through many talks and deals, he convinced the studio to let him release his cut, but with the new title "Hard Eight". Anderson later said this experience taught him that doing your best to make the best possible movie was only "half the job" when being a director. The other half was dealing with all of the egos involved.
When Jimmy (Samuel L. Jackson) and Sydney (Philip Baker Hall) have their confrontation, Jimmy mentions that he knows Sydney's friends Floyd Gondolli and Jimmy Gator. In Paul Thomas Anderson's next movie, Boogie Nights (1997), Philip Baker Hall plays Floyd Gondolli. In Anderson's followup to Boogie Nights, Magnolia (1999), Philip Baker Hall plays Jimmy Gator.
Paul Thomas Anderson, on the DVD commentary, admitted to successfully pulling off the casino rate card trick shown in the film, several times.
Assistant cameraman Michael G. Riba turned down two weeks of work on Waterworld (1995), which paid better, to work on this movie. Riba has been the assistant cameraman on every Paul Thomas Anderson film since.