The one useful thing we learned was how Twitter defines engagement. But that wasn't actually part of the source and was published separately! This type of transparency about how algorithms are configured should be considered essential, and doesn't require release of source code.
ALT Type of engagement
Weight
Probability the user will Like the tweet
0.5
Probability the user will retweet the tweet
1.0
Probability the user replies to the tweet
13.5
Probability the user opens the tweet author profile and Likes or replies to a tweet
12.0
Probability (for a video tweet) that the user will watch at least half of the video
0.005
Probability the user replies to the tweet and this reply is engaged by the tweet author
75.0
Probability the user will click into the conversation of this tweet and reply or Like a tweet
11.0
Probability the user will click into the conversation and stay there for at least 2 minutes
10.0
Probability the user will react negatively (requesting “show less often” on the tweet or author, block or mute the tweet author)
-74.0
Probability the user will click report tweet
-369.0