Age of Empires III released in 2005, and is no longer on sale after 19 years. This has been confirmed by a message on Steam page of the remake, Age of Empires III: Definitive Edition, released in 2020.
“From today, Age of Empires III (2007) will no longer be available for purchase. After many years of support, we will be retiring the title from sale”, the said. Then, on October 30, the online servers will close, due to the techonology no longer being supportes.
Age of Empires III: Definitive Edition will continue to be supported, of course, and will receive a free update on October 24 with quality of life and balance changes.
However, they have also announced that the new DLC for Age of Empires III: Definitive Edition has been delayed to a future date, and won’t release this year as it was previously announced. This is due to the many active projects in the franchise, including support for Age of Empires II: Definitive Edition, Age of Empires IV and Age of Mythology: Retold.