According to a few tweets the Sword Art Online: Alicization will have 2 cours. Previous reports suggested that season 3 could possibly have four cours. If you don’t know what cours are, they are the number of episodes in a season. For example one cour is 12-13 episodes while two cours is 25-26 and so on. However, according to the latest rumors it seems that maybe season 3 will have 2 cours all adding up to around 48-50 episodes. Take a look at the tweet below.
A person who participated in the Japan premiere of SAO Alicization's first episode claims that during a talk show segment of the event, Matsuoka Yoshitsugu (voice of Kirito) mentioned that Alicization's 4 cours will be split into 2 x 2-cour parts.https://t.co/WTsITIecA6
— SAO Wikia (@sao_wikia) September 15, 2018
Since there is no official confirmation from the studio as of yet, please take this with a grain of salt. Sword Art Online: Alicization is the longest arc in the series, and is also considered the best arc. We recently discussed the the release date for the series which you can see here.
Source: SAO Wikia, Comicbook