NS has mentioned the release date of the Dota 2 Compendium

Streamer and former professional esports player Yaroslav "NS" Kuznetsov speculated about the release date of the thematic update for the upcoming The International 12 (2023) Dota 2 Championship.

NS suggested that we should expect the release of the update with the compendium (a type of Battle Pass) on September 28. 

Valve has not yet provided a specific date, but they plan to release the compendium by October 1. It is quite possible that it will be released on September 29. Typically, updates are released on Wednesday night or Thursday night, so there is a high probability that the new Battle Pass will appear on September 28-29.