The Halloween Apocalypse: Flux: Chapter One had an Audience Appreciation Index score of 76.
The Appreciation Index or AI is a measure of how much the audience enjoyed the programme. The score, out of a hundred, is compiled by a specially selected panel of around 5,000 people who go online and rate and comment on programmes.
The previous series opener, Spyfall: Part One (New Year's Day 2020) achieved a score of 82, whilst the most recent episode, New Year's Day adventure Revolution of the Daleks, achieved a score of 79. The thirteenth Doctor's era as a whole has a a current average score of 80.
The score of 76 is the lowest achieved for the series since Love & Monsters in 2006.