In what year did Tumblr introduce the Tumblr+ subscription service? The correct year is 2021.
Tumblr launched Post+ on July 21, 2021, initially for selected beta users. The service allowed bloggers to monetize their content by offering paid subscribers access to subscription-only posts.
The service was later discontinued because of low usage, with Tumblr removing it in January 2024. Contemporary reporting sometimes referred to the offering as Tumblr+, but the official product name was Post+.
Therefore, 2021 is the supported answer among the available options, although the question’s product name should be corrected to Post+.