Niantic recently announced that Pokemon Go players worldwide managed to unlock the Ultra Bonus by completing over 36 million research tasks for Professor Willow. The bonuses will span three weeks in the good old back to back fashion.
Niantic officially announced that Ultra Bonus will be activated in September 2019 but with the meaty news coming on 20 August 2019.
The first round of Ultra bonus, named Professor Willow's Global Challenge Ultra Bonus Week 1, will kick off on 2 September 2019 at 13:00 PDT / 06:00 AM UTC and will continue on for a week, as the name would suggest, wrapping up on 9 September 2019 at the same time.
Round two's name is the same mouthful, except it's Week 2 at the end. This one will start just as Week 1 concludes and wrap up on 16 September 2019.
Round three follows the same rules as the previous two and will finish on 23 September 2019.
Each week will feature different bonuses though. Week 1 will have a Pokemon that was apparently never seen before and it will hatch from eggs the regular way, enriching the players' Jahto Pokedex.
Week 2 will have Pokemon all over the globe joining in for celebration which could be a hint that regional exclusives will become non-exclusive temporarily. Furthermore, a Mythical Pokemon will start appearing in raids and players will be able to catch it but it's currently unknown which one it is.
Week 3 seems to be a mashup of the previous two weeks while offering its own spin on things. Certain "unusual" Pokemon will start appearing in the wild during this week, additional opponents are coming to raids and players will be filling up their Kanto Pokedex this time around, with Pokemon that were previously region locked.