This answer assumes you're asking about the model still currently available, as the MacBook Air hasn't been upgraded since early 2015 (9 March 2015 to be exact), although there was a very minor spec update in June due to a 12.5% increase in the processor's speed. This, however, has no impact on the integrated GPU being used and even Apple's website does not list this as a "new" model.
Originally this model was only rated by Apple as supporting a single external display of up to 2,560 x 1,600 pixels. However, it was found to actually support Ultra HD (i.e. 4K) resolutions of 3,840 x 2,160 pixels and Apple officially revised their specs.
Most resources (including everymac.com) imply that the MBA only supports a single external display. However, this is not strictly the case, so long as you're using Thunderbolt displays.
According to Apple:
These Thunderbolt-capable Mac computers can support up to two connected Apple Thunderbolt Displays:
- MacBook Pro (2011 and later)
- MacBook Air (Mid 2012) and later
- iMac (2011 and later)
- Mac mini (2011 and later)
Source: About Thunderbolt ports and displays
So, you can use two Thunderbolt displays with a MacBook Air, but you will need to daisy chain them. Note this applies to all models of MBA from Mid-2012 and later. In some cases users have had to do this by, for example, connecting a Thunderbolt display directly to the MBA and then connecting another powered Thunderbolt device (e.g. a Thunderbolt drive) to the display, and then connecting your second Thunderbolt display to the Thunderbolt drive.
I have seen setups in which users have connected one Thunderbolt display directly to the MBA's Thunderbolt port and a second DVI display via a USB-DVI adapter. Some seem to work quite well, others not so much. If your intention is to just do some word-processing and browsing, this'd be fine, but if you wanted to use the display for more intensive tasks, I would not go this route.