[jhowell]

I am surprised that it took this long for KFX to appear in Kindle for PC. I suspect that it was held up waiting for the accessibility software to be developed to support it. I think it likely that 1.19 will be made available by default for new downloads within the next few weeks and that support for all of the previous versions will be withdrawn within a year.

So the K4PC loophole is closing and I think owners of PW1 or older Kindles are safe. For me the burning question is whether or not Amazon is going to change "Download & transfer via USB" for newer Kindles so that it delivers KFX format.

It has been pointed out that KFX format requires multiple files per book and so would not be suited to download & transfer. But it would be easy for Amazon to just zip these files into an archive and have the kindle unzip them upon receipt. In fact I saw signs that Amazon was working on that type of functionality over a year ago.

Changing "Download & transfer via USB" to deliver KFX would have advantages for Amazon. Customers would then have the same reading experience (enhanced typesetting, page flip, etc.) as they do when books are sent to the devices directly. The current system results in an inconsistent user experience that must cause support headaches for them.

Why hasn't it been changed already? One problem with making this change is that they would need to track what level of support for KFX is in the firmware on the device being targeted.

KFX isn't a static format. It was designed so that new features could be added over time. Each KFX book has a list of "content features" that it relies on and only firmware supporting those features can display the book correctly. If the KFX version of a book uses features that a device doesn't support then KF8 is delivered instead. (One reason why KF8 isn't going away anytime soon.)

One new feature that Amazon has already deployed, but I don't remember being mentioned by anyone else, is the ability to "upgrade" books in the background. This allows books on a device originally delivered in KF8 format to be replaced with the KFX equivalent when the device is online. Thus books can be migrated to KFX after a device is updated with newer firmware.

Perhaps they consider this migration feature to be enough of a solution and will keep "Download & transfer via USB" using KF8 as it does now.