On June 15, 2015, during the Ubisoft press conference at E3, Ubisoft released multiple new trailers for the game. The trailers, which were also uploaded to the Ubisoft YouTube channel, showed some of the environments and gameplay elements found in Rainbow Six Siege. Ubisoft also announced that Terrorist Hunt, a co-operative multiplayer mode introduced in the previous Rainbow Six games, would return in Siege. It was also announced that players who purchased Siege for the Xbox One could download Tom Clancy's Rainbow Six: Vegas and its sequel, Tom Clancy's Rainbow Six: Vegas 2 for free.
The game featured 11 maps at launch, with more added to the game as free downloadable content. According to Ubisoft, the decision was made as they wanted to extend the game's longevity. The game supports microtransactions for players who want to speed up their progress. However, items bought by players using real-life currency are designed to not affect or change the gameplay.
Tom Clancy's Rainbow Six Siege received \"mixed or average\" reviews on Metacritic getting a metascore of 79/100 on PC, 73/100 on PS4, and 74/100 on Xbox One. The game received an overall positive reception from critics, with praise mostly directed to the game's tense multiplayer and focus on tactics. However, the game was criticized for its progression system and its lack of content. Initial sales were weak, but the game's player base increased significantly as Ubisoft adopted a \"games as a service\" model for the game and subsequently released several packages of free downloadable content. Several years after the game's release, some critics regarded Siege as one of the best multiplayer games in the modern market due to the improvements brought by the post-launch updates. The company partnered with ESL to make Siege an esports game. In December 2020, the game surpassed 70 million registered players across all platforms. 59ce067264