I’ve heard that Jonathan Stroud is planning to write a new Bartimaeus book someday.

Have you got some up-to-date news? Please, I have to know when it will be released.

And do you think it will take place before "The Amulet of Samarkand" or after "Ptolemy’s Gate"?
I hope after the third book. Bartimaeus’ past is great and so on, but I really like to know what’s going on with Kitty and Bartimaeus.

All he's said is that he's open to the possibility of writing more; I'm pretty sure there's no concrete plans, and it's definitely not what he's working on at the moment.

I doubt he'd make a sequel to Ptolemy's Gate.

Honestly, I hope if there is another book, it will be about the whole Akhenaten/Nefertiti rise and fall from power. It's just such an interesting and mysterious period of history. For instance, Nefertiti disappears from the historical record after the fourteenth year of Akhenaten's rule. Not to mention the whole monotheistic religion thing. Anyway, there were a LOT of footnotes about it in the books, so it seems like it's something JS might consider if/when he gets around to writing a book 5.