Emma Roth, writing for The Verge:

Twitter will no longer allow users to promote their presence on certain social platforms, including Facebook, Instagram, Mastodon, Truth Social, Tribel, Nostr, and Post. In a post outlining these changes, Twitter says it will take action against users that violate this policy “at both the Tweet level and the account level.”

This means users can no longer include links to their profiles on other social networks (or even include their handle without a URL) in their Twitter bio, nor can they link to their posts on banned platforms unless it’s a cross-post. Twitter also says it may suspend accounts “used for the main purpose of promoting content on another social platform,” and will no longer allow users to link to third-party link aggregators, like Linktree or Lnk.bio. Despite this, Twitter is still fine with the paid promotion of these banned platforms:

We recognize that certain social media platforms provide alternative experiences to Twitter, and allow users to post content to Twitter from these platforms. In general, any type of cross-posting to our platform is not in violation of this policy, even from the prohibited sites listed above. Additionally, we allow paid advertisement/promotion for any of the prohibited social media platforms.

Twitter says it will remove any tweets that contain violations of the policy, and could temporarily suspend users with links to banned social platforms in their profiles. It will also take action against users who try to get around this policy by cloaking URLs to other platforms or “spelling out “dot” for social media platforms that use ‘.’ in the names to avoid URL creation, or sharing screenshots of your handle on a prohibited social media platform.”

From Twitter's newly added "Promotion of alternative social platforms policy":

Twitter is where the public conversation is happening, and where people from all over the globe come to promote their businesses, art, ideas, and more. We know that many of our users may be active on other social media platforms; however, going forward, Twitter will no longer allow free promotion of specific social media platforms on Twitter.

At both the Tweet level and the account level, we will remove any free promotion of prohibited 3rd-party social media platforms, such as linking out (i.e. using URLs) to any of the below platforms on Twitter, or providing your handle without a URL.

The list of offenders include:

• Facebook, Instagram, Mastodon, Truth Social, Tribel, Post and Nostr
• 3rd-party social media link aggregators such as linktr.ee, lnk.bio

Seems about right.