WARNING: The following contains spoilers for One Piece Chapter #1018, "Jimbei vs. Who's-Who," by Eiichiro Oda, available in English via Manga Plus and Viz Media.
CP-0 have been keeping a close eye on One Piece's ongoing Onigashima raid. More specifically, how the numbers are fluctuating on both sides of the battle. Thanks to O-Tama's Devil Fruit powers and the fall of two of the Tobiroppo, a large chunk of the Beast Pirates turned traitor recently and began fighting alongside the samurai. And while they are still outnumbered, an important update in Chapter #1018 shows things are beginning to look up for the Luffy and the Alliance.
The government entity CP-0 act as an intelligence-gathering organization within Cipher Pol. They have been seen several times throughout the series, first during the events in Dressrosa and at several times during major events since, like going undercover to gather intel during the wedding between Sanji and Charlotte Pudding. After being invited to Onigashima by Orochiare, they're now in Wano Country to look for weapons for the World Government, where they have been keeping a close eye on the battle between the Beast Pirates and the Alliance.
Around the beginning of the battle, the count was roughly 30,000 Beast Pirates vs. 5,400 on the Alliance's side. After the battle began, roughly 5,000 soldiers fell, bringing those numbers down to 24,000 vs. 3,000. However, after Queen infected his own men with the Ice Oni Virus, the Pleasures and Waiters turned against him, adding 4,000 men to the Alliance's numbers. This made the fight a little more balanced at 20,000 against 7,000. Another big turn occurred when O-Tama used her Devil Fruit powers to take control of anyone who ate her dangos, which included the majority of the Headliners and Gifters. After she gave the order for them to fight on the side of the samurai, 300 of them turned on their own crewmates. Once the Headliners turned, so did around 1,000 of their followers. Not only this, but they took out 1,000 of the Beast Pirates, meaning in total they have lost over 10,000 of their men.
This brings the current count to 16,000 against 9,000. It now appears that slowly, Luffy's Alliance is beginning to catch up to the Beast Pirates. Those numbers could continue to rise now that Ulti and Page One have fallen, thanks to Bao Huang's accidental announcement of the event. Now that Who's-Who has also apparently been defeated by Jimbei, the low morale of the Pirates could lead to more traitors among their ranks.
Another major event that could lead to more Beast Pirates turning in One Piece would be the return of Luffy, who was previously believed to have been killed by Kaido until Momonosuke announced the Straw Hat's intent on returning to battle. However, because some of the more powerful Beast Pirates have already joined the samurai, it could be that they are enough to balance out the fight to the point they won't need more to turn, especially considering they are Artificial Zoan users. The next few chapters of the One Piece manga will continue to be crucial in determining Wano's future.