Mashable: Substack writers cannot embed tweets in their posts. Twitter users cannot retweet or like tweets with Substack links.

It appears that Twitter may currently be feuding with the newsletter platform Substack.

Substack writers began noticing that they were no longer able to embed tweets when creating a post on Substack yesterday. While this could've been just a technical issue, perhaps related to Twitter switching over to its new yet heavily-criticized API plans, it appears now that something more is going on here.

Twitter is now blocking likes, retweets, and comments on tweets that include a link to a Substack newsletter. In addition, Twitter users cannot pin a tweet that includes a Substack link to their profile.

The timing of these issues, which seem to solely be affecting Substack links, is peculiar. Just one day before these Twitter errors started appearing, Substack announced a new feature called Substack Notes. It basically brings a social media-like feed with tweet-like posts to the newsletter platform. It's not exactly a Twitter competitor, as it exists within the newsletter platform's ecosystem, but it sure does look like one.

Yesterday, when Mashable reached out to Substack regarding the embed tweet issue, a spokesperson provided us with the following statement.

"We’re investigating reports that Twitter embeds and authentication no longer work on Substack," the Substack spokesperson said. "We are actively trying to resolve this and will share updates as additional information becomes available."

Today, however, when Mashable reached out regarding the blocked interactions on tweets that include Substack links, we received a statement from Substack's founders Chris Best, Hamish McKenzie, and Jairaj Sethi.

"We’re disappointed that Twitter has chosen to restrict writers’ ability to share their work," the founders of Substack said in a statement provided to Mashable. "Writers deserve the freedom to share links to Substack or anywhere else. This abrupt change is a reminder of why writers deserve a model that puts them in charge, that rewards great work with money, and that protects the free press and free speech. Their livelihoods should not be tied to platforms where they don’t own their relationship with their audience, and where the rules can change on a whim."

Researcher Jane Manchun Wong, an expert in discovering upcoming and unreleased features hidden within the code inside apps, first noticed Twitter's latest move last night.

"Server errors with either: Authorization: Engagements are limited on tweet [id] or Authorization: Some actions on this [username] Tweet have been disabled by Twitter. (425)," Wong tweeted from her @wongmjane account, describing what she was able to see in the inner workings of Twitter.

As readers can see in the above screenshot of the test tweet posted by Wong, users cannot like or retweet a tweet including a Substack link. As Twitter's recently publicly-released recommendation algorithm source code showed, these interactions greatly affect how far a tweet goes on a platform. As one can see, the lack of interactions on Wong's tweet has greatly diminished the number of views on her post.

One of the first to notice the embed issue was Garbage Day newsletter creator Ryan Broderick who shared a screenshot on Thursday of the prompt he was receiving on Substack.

Twitter's move to block Substack links is certainly a bizarre one. Twitter itself once ran a Substack alternative called Revue. However, the company shut down the newsletter platform shortly after Musk took over. Both Twitter and Substack share the same tech VCs as investors. Many of the Twitter users that Musk frequently interacts with run Substack newsletters. The Musk-approved Twitter Files were predominantly distributed via writer Matt Taibbi's own Subtack newsletter. 

Elon Musk has repeatedly touted that his reasons for acquiring Twitter was to help level the playing field, making it a more "free speech" platform, on what he considers to be the "de facto town square."

However, it appears that's only the case if you don't happen to also offer Twitter's users an alternative platform.