Is Dragon Ball GT Canon?

The basic timeline of the Dragon Ball series is well known: (1) Dragon Ball, (2) Dragon Ball Z, then (3) Dragon Ball GT.  However, there are groups of fans who claim that Dragon Ball GT is not canon because it was not part of Akira Toriyama’s manga series, partly making this claim because they did not enjoy Dragon Ball GT as much as the original series.  They make their claim even though Akira Toriyama never claimed that Dragon Ball GT is non-canon, in fact, he has shown himself to have positive feelings towards this series.  He oversaw the anime series production of Dragon Ball GT in the very same way that he oversaw the anime adaptions of Dragon Ball and Dragon Ball Z and is credited as the author in the ending credits of GT.

Akira Toriyama came up with the very name of the series, designed some of the characters and objects such as Giru and the spaceship traveled in, and sketched the GT logo concept.  Akira Toriyama arranged the series main cast and drew multiple pictures of GT Goku, Pan, and Trunks adventuring on various planets.  He also drew a promotional picture of Super-Saiyan 4 Goku as his seal of approval on the series and referred to the GT staff as “excellent!” and stated that watching Dragon Ball GT makes him: “happy” and he “enjoys it.”  He said that the series animator, “animator Nakatsuru-kun is amazingly skilled, and mastered the peculiarities of my drawings.”  The characters and events of Dragon Ball GT have also been including in various official video game releases.

Some dissatisfied fans point to the inconsistencies in Dragon Ball GT to claim that it is not canon, however, the inconsistencies and contradictions in the other various Dragon Ball series’ are much higher than GT's, especially in Dragon Ball Super which probably contradicts Dragon Ball Z more than any other variation of Dragon Ball including the movies.  Especially after the release of Dragon Ball Super, trying to discredit Dragon Ball GT by inconsistencies is laughable.

Akira Toriyama himself refers to Dragon Ball GT as “a grand side-story of the original Dragon Ball.”

The closest thing we have to discrediting Dragon Ball GT is a statement made by the Dragon Ball Z voice actor Christopher Sabat whose opinion was that Dragon Ball GT is “not even canon anymore,” after the release of the “Dragon Ball: Battle of the gods” movie.  Although he does not really have the authority to make an official statement about a part of the series no longer being canon, his opinion is valuable and the way I take it is, some things in the new series: "Dragon Ball Super" are going to override some of the canon in GT because of the contradictions and inconsistencies between the two series, however, there are theories of how the contradictions can be fixed or can fit together by a string of events between the two series.  Only time, or a new official statement by Toriyama, will tell.  As far as we know, GT remains canon rather fans like it or not.