On 2 January 2012, Channel 4 orchestrated a special "mash-up night" to celebrate its 30th anniversary, which involved two shows on the network merging their formats. One combination depicted Countdown and 8 Out of 10 Cats. Jimmy Carr took over as host alongside Rachel Riley. Sean Lock and Jon Richardson competed as contestants and Joe Wilkinson joined Susie Dent in Dictionary Corner. The show consisted of four letters rounds, two numbers rounds and the conundrum, interspersed with 8 Out of 10 Cats-style banter.
A second special episode called 8 Outs of 10 Cats Does Countdown was broadcast on 24 August 2012 as part of Channel 4's "Funny Fortnight". Once again, Carr was host, Lock and Richardson were contestants, and Riley and Dent returned to their roles. In Dictionary Corner, Susie was joined by David O'Doherty. Wilkinson and past contestant Clarke Carlisle also featured. In this edition there were five letters rounds, four numbers rounds and a conundrum.
Two additional specials aired in April 2013, with Lee Mack playing against Richardson, as Lock was unwell. In addition to the regulars, these specials also featured Rhod Gilbert, Rob Beckett, Stephen Mangan and Richard Osman as contestants, Tim Key and Henning Wehn in Dictionary Corner, and Wilkinson as Riley's "personal assistant".
On 9 July 2013, Channel 4 announced it had commissioned a full series of 8 Out of 10 Cats Does Countdown to air later in the summer. Six episodes aired from July to September. The final episode of the series was part of Channel 4's "80s Night". The opening sequence for the final episode featured the standard title sequence for 8 Out of 10 Cats interspersed with images of the title sequence that Countdown used in the 1980s. Another series of six episodes were broadcast between 3 January and 28 February 2014.
Recordings for a new series of six episodes began on 19 May 2014. The first episode was broadcast on 6 June 2014, with the series originally scheduled to end on 11 July 2014; however, it was stretched to seven episodes and therefore ended on 18 July 2014. Another four episodes were recorded on 2 and 16 July 2014; the first recording was episode seven of Series 3. The next three episodes began airing from 5 September 2014 and concluded on 19 September 2014.
Rachel Riley confirmed via Twitter on 19 September 2014 that more episodes of 8 Out of 10 Cats Does Countdown would be filmed for 2015. It was announced in November that the show would have a Christmas special, followed by a new six-episode series. Episodes for the fifth series were recorded throughout December 2014 with one of the episodes also being recorded on 1 February 2015. Recording for series 6 began on 5 March 2015 and its broadcast in May 2015, with further recordings in May, June and July 2015.
Further recordings also took place in November and December 2015. Another Christmas Special aired on 8 December 2015 and another six-part series began in January 2016. A further series followed in 2016, beginning in August and running through October. A seventh series began broadcast on 13 January 2017.
Unlike the traditional game of Countdown, each edition lasts one hour (except for the 2012 special, which lasted 30 minutes). Due to the comedy interspersed between and during rounds, the game does not consist of the standard 15 rounds. The first few specials had different numbers of rounds ranging from 7 to 10. In the two full series of the show, there were either 8 or 9 rounds. The first three quarters of the show contained a letters round and a numbers round; the last section had a letters round, a numbers round (if there was time) and a conundrum.
The letters and numbers rounds are the same as in Countdown, and there are also "Teatime teasers". The conundrums and teatime teasers typically contain sexual words or innuendos; one example is "GONADTIP" (clue: "One way to become a parent", answer: "ADOPTING").
Whilst the clock is ticking, as the contestants attempt to find a word or reach the target from the numbers within 30 seconds, Carr often takes part in some form of unusual or non-sequitur activity such as trying to get a dog through an obstacle course, eating dog biscuits or enticing a bird of prey to fly onto his arm. Rachel Riley is occasionally involved in these segments.
Apart from during the first two specials, there are two contestants on each team, with Jon and Sean as permanent guests. During some rounds, contestants all offer an answer but only the best answer from each team counts. During some rounds, one player per team is nominated to give an answer.
A celebrity appears in Dictionary Corner, and, after each numbers round, they present a poem, song or other comedic segment. Susie Dent's "Origin of Words" section does not appear, but is instead replaced with an additional segment from the guest.
In earlier episodes, Joe Wilkinson appeared as Rachel's assistant in the second half of the show, often dressed in costume whilst using props. The humour continued throughout the series, such as Wilkinson offered special prizes, replacing letter tiles with symbols or turning up despite having been "fired". During Wilkinson's sketches Robert Deaton (as Wilkinson's half-brother Fabio) sometimes appears. Since 2016, Wilkinson has appeared sporadically as a contestant.