How to tell if Macbook is using 802.11ac
When you're connected to the Wi-Fi network, hold down option and click the Wi-Fi icon in the OS X menubar. You'll see additional details about your connection, including one item labelled PHY Mode:. That will show you whether you're connected via 802.11ac, n, g, etc.



There's also a Channel: entry that tells you the radio frequency and channel.