The novel was a collaborative effort between Kubrick and Clarke based on earlier short fiction by Clarke. Kubrick chose not to use the elements of the story, just as I've written. Because of that, Kubrick did not receive any credit for the novel.
The ending of the novel is deliberately glossed over because of Kubrick's personal creative history. And it sucks.
OK, the plot of the novel is spelled out in Wikipedia, and deviates significantly from the film. I can only say that as a “collaborative effort” it qualifies in my mind as a screenplay, however emended by Kubrick in the end.
Also, the book I cited ( by its cover ) is a very trashy compendium of various commentary on the film, and provides only anecdotal facts related to the film’s production, except that it does include the text of THE SENTINEL. Nevertheless it remains dear to my heart.