  Bluesky is a Twitter-like decentralized social media platform that has
recently grown in popularity. After an invite-only period, it opened to the
public worldwide on February 6th, 2024. In this paper, we provide a
longitudinal analysis of user activity in the two months around the opening,
studying changes in the general characteristics of the platform due to the
rapid growth of the user base. We observe a broad distribution of activity
similar to more established platforms, but a higher volume of original than
reshared content, and very low toxicity. After opening to the public, Bluesky
experienced a large surge in new users and activity, especially posting English
and Japanese content. In particular, several accounts entered the discussion
with suspicious behavior, like following many accounts and sharing content from
low-credibility news outlets. Some of these have already been classified as
spam or suspended, suggesting effective moderation.
