Amazon has plenty of issues to resolve before its Prime Air delivery drones stand a chance of getting in the air, but CEO Jeff Bezos says the company is rapidly testing more prototypes. In a letter to shareholders published with the SEC, Bezos said that the Prime Air team is "already flight testing our fifth and sixth generation aerial vehicles, and we are in the design phase on generations seven and eight." We don't know how much innovation is actually happening between these generations, but the team will have to solve the problem of making a craft with enough power and battery life to travel 10 miles with up to 5 pounds of cargo, something that's currently no easy task. From there, they'll have to find solutions for more complicated problems, and some of Bezos' plans — like having his octocopters land right on someone's front lawn — may not be feasible right now. He's previously said that Prime Air could be four to five years away, and he certainly didn't contradict that in the letter.

Bezos also highlighted the recent launch of the Fire TV, Amazon's combination set-top box and lightweight game console. There are few meaningful statistics in the letter, but he says that the Prime Instant Video streaming service is experiencing "tremendous growth" in customers, repeat usage, and number of streams. Prime service as a whole rose from $79 a year to $99 in March, but Bezos only highlighted features added over the past few years and said that there were "tens of millions of members" worldwide. He also took partial credit for the FAA's reversal on in-flight electronics, which were officially allowed during takeoff and landing last year. "Our public policy team, with the help of many allies, worked patiently for four years on this, at one point loading a test plane with 150 active Kindles," he wrote. "Yes, it all worked fine!"

Amazon has run its own Android ecosystem since it announced the original Kindle Fire in 2011, and today, Bezos announced that over 200,000 apps were available to download in roughly 200 countries. Bezos says this means it's almost tripled in size in the past year, but the raw number isn't that impressive compared to the iOS App Store or Google Play, both of which passed a million apps in 2013. Amazon notoriously refuses to release numbers about how many Kindles it's sold, though, so it's hard to actually tie that to the platform's overall success. Developers are also still in the early stages of bringing apps and games to the Fire TV, although the experience so far is actually pretty good. Bezos' letter is available on the SEC's website, despite an odd phishing warning.