Microsoft's most eye-catching E3 2015 announcement was the addition of backwards compatibility to the Xbox One. It means some Xbox 360 games will be playable on the console.
When it made the announcement, Microsoft used BioWare's action role-playing game Mass Effect to demonstrate the technology.
"It was surprising," Sony Worldwide Studios boss Shuhei Yoshida told Eurogamer editor Oli Welsh when asked for his reaction.
"I didn't think it was possible. There must be lots of engineering effort. They talked about 100 games, but what kind of games will be included? Is it smaller games or big games? We don't know."
We won't see the proper launch of backwards compatibility on the Xbox One until this autumn, but you can play around with a handful of games right now, if you're an Xbox Preview Member.
Eurogamer YouTube chap Ian Higton went hands on with Xbox One backwards compatibility, and was able to download BattleBlock Theatre, Perfect Dark, Super Meat Boy and a handful of others straight to his Xbox One hard-drive, where they run via a fully emulated Xbox 360 system - complete with last-gen menus and notification pop-ups (check out his report in the video, below). Any game not stored on your Xbox 360 hard-drive will need the disc to launch it, and save data transfers between consoles. Microsoft has said old games you don't own will also be available to buy further down the line.
Yoshida's question about whether backwards compatibility will work with bigger games brings to mind an ongoing survey Microsoft is conducting, which asks Xbox One owners which games they would like to see added to the backwards compatibility list. Rockstar's Red Dead Redemption - what would certainly be considered a "big game" - leads the pack.
So what about PlayStation 4? Now that Microsoft has managed to get Xbox One running Xbox 360 games, will Sony get the PlayStation 4 running PS3 games?
It doesn't sound like it.
"PS3 is such a unique architecture, and some games made use of SPUs very well," Yoshida replied when quizzed by Eurogamer.
"It's going to be super challenging to do so. I never say never, but we have no plans."
What does Yoshida mean here? Here's Digital Foundry's Richard Leadbetter to explain:
At least PS4 has PlayStation Now, which lets you play PS3 games on your PS4 via streaming. But, well, it looks like it's going to be pretty expensive.