This is thanks to an alleged leaked presentation slide as reported by Mojandroid.sk (via Xperia Blog) from Sony Slovakia. As you can see in the photo above, it shows the company’s plans for the Android 7.0 Nougat update. Assuming the timing is applicable for all markets they operate in, the Xperia X Performance and Xperia XZ should get their update in October.
This is followed by the Xperia X and X Compact which should get theirs in November, and the Xperia Z5 series, Z3+ and the Z4 Tablet will get the update in December. The Xperia XA and Ultra are also mentioned and they should expect their updates in early 2017, although no months are specified.
As for those in the US, you might have to wait a bit longer as updates are usually sent to carriers for approval before being released, so there is an additional step which could delay the update compared to its international and unlocked handsets. Of course these dates could be subject to change, so don’t treat them as concrete yet but more as a rough timeframe.