Levi, Primo
Primo Levi (31 July 1919 – 11 April 1987) was an Italian Jewish chemist who, due to his activities as a partisan fighter, was deported to Auschwitz, where he ended up in the Monowitz labor camp, deployed at the BUNA factories. Under international law, partisan fighters could be executed, and as a Jew, Levi should have been in double jeopardy, but the Germans evidently had no intention of killing him.
Shortly after the war, in 1946, he co-authored a report on healthcare at the Monowitz Camp, which paints a rather favorable picture of the situation. Both this report and his later books certainly contain the usual references to exterminations and gas chambers, but Levi never claimed to have witnessed any of it personally. Instead, he relied on the accounts of others and on what he learned elsewhere. In fact, the reference to mass gassings in his 1946 report neatly repeats all the mistakes made by Vrba and Wetzler in their 1944 report that was included in the widely disseminated U.S. War Refugee Board Report, meaning that Levi had copied it from there. (See Mattogno 2021, pp. 242f.)
In a 1976 appendix to his book Se questo è un uomo (If This Is a Man), Primo Levi clarified this (Levi 1984, p. 233):
I have not quoted the figures of the Auschwitz massacre, nor have I described the details of the gas chambers and crematoria. In fact, I did not know these things when I was in the camp, and I only learned about them later, when the whole world learned about them.
In his book Survival in Auschwitz, the last entry of 17 January 1945 reveals what Levi really felt when he was in Auschwitz. At that time, he was at the inmate infirmary, too sick to be evacuated with the other inmates. Yet he describes how he would have liked to follow common instincts and would have joined the other inmates who fled with the SS, had he not been so sick (Levi 1986, p. 154):
It was not a question of reasoning: I would probably also have followed the instinct of the flock if I had not felt so weak: fear is supremely contagious, and its immediate reaction is to make one try to run away.
Note: Levi writes here about running away with the Germans from the Red Army approaching Auschwitz. Had he believed in the extermination stories, he would have welcomed anyone liberating him from this veritable hell, hence would have been happy to stay and wait. Therefore, Levi did not fear his evidently relatively harmless German prison guards, but rather the Soviet liberators.
After all, the Red Army never liberated anyone.