Stephen Fry and Alan Davies were originally cast as the leaders of the "clever" team and the "stupid" team, respectively. Michael Palin was asked to be the host, but he didn't feel he was right for the role. After Fry and Davies settled into their roles, the idea of having two teams was discarded.
Stephen Fry revealed that there is one panelist who insists on seeing the questions in advance so that he or she can prepare their answers. Fry refused to name the person but did confirm that it was neither Alan Davies nor Rob Brydon.
The BBC and Talkback issued an apology in January 2011 after the Japanese Embassy made a complaint over a question and answer about Tsutomu Yamaguchi, the only man officially recognized as a survivor of both the Hiroshima and Nagasaki A-bomb explosions, who was described on the show as "either the unluckiest or the luckiest [man in the world], depending on which way you look at it".
Each series has questions related to a subject matter beginning with a corresponding letter (i.e. in the first series, every question was related to things beginning with A, the second series used the letter B, etc.).
The Qi theme tune actually has a secret message hidden within it, spelling out www.alan0andstephenhero.com in Morse code. In 2016 (when this titbit was first revealed on the show), a real link to the show's official webpage was created from this URL.
The original BBC scheduling plan for the series, when they introduced the additional extended broadcast edit, was to have the 30 minutes edit shown first, with the corresponding extended XL edit shown several days later, usually on Saturday evening. However, due to unavoidable scheduling conflicts and regional variations, some of the extended X edit version's first-run may not appear for several weeks until after the shorter version was first broadcast. This has the knock-on affect of creating some discrepancies in the broadcast dates between the 'regular' versions and their respective XL versions, even though there may be just a gap of a few weeks.