From Wikipedia:
Although Stutthof is not considered to be a death camp orthodox Holocaust historians claim that Stutthof had a homicidal gas chamber. I have previously written about how it is admitted that the US Army lied about the use of a homicidal gas chamber in Dachau and there is no evidence to back up the claims of a gas chamber in Ravensbruck. Could it be possible that the alleged homicidal gas chamber in Stutthof is just another fabrication of Allied propaganda?
In Jürgen Graf and Carlo Mattogno’s book, Concentration Camp Stutthof—Its History & Function in National Socialist Jewish Policy a thorough investigation of the camp is presented and the following is the conclusion drawn:
Before we get into the matter of the gassing of humans at Stutthof it is important to know that there was a building that served as a gas chamber at Stutthof and it still stands to this day. However, this building was built to be a delousing chamber to save lives by curbing the spread of deadly diseases.

Like so many claims in the official Holocaust narrative, the assertion that humans were gassed at Stutthof relies on witness testimony. And like so much of the witness testimony concerning the Holocaust, examination of the claims made shows the witnesses to be unreliable:
Here are some problems with Aldo Coradello’s testimony:
Further observations from Mark Weber cast more doubt on the the existence of a homicidal gas chamber:
And we have a few more observations made by David Cole:

It’s clear that the claim of gassing humans is nothing more than atrocity propaganda to bolster the overall narrative of the Holocaust. Because what Nazi camp would be complete without the homicidal gas chamber?