The Metal Gear series has sold more than 56.1 million copies

The Metal Gear series has sold more than 56.1 million copies, as of the end of June 2020. The updated figure comes from the Metal Gear in Concert official website.
Update: the number was also provided in Konami’s financial report from late July.

The previous number was 53.8 million copies by the end of March of 2018, meaning a total of 2.3 million games have been sold in the last two years. There haven’t been any new releases in the series during that time. Metal Gear Survive, which came out in February of 2018 was the last installment to be released.

Konami has been mostly quiet about the series during these last two years, with senior brand and business development manager Richard Jones stating in a recent interview that the Konami IP are being looked after by the development teams in Japan.

Source: Metal Gear in Concert, Konami