Google has released new LMY48M factory images for Nexus 6, Nexus 9 (LTE and WiFi), Nexus 5, Nexus 7 (2013, WiFi), Nexus 10, and Nexus 4 devices that fixes minor security issues and bugs. Google released LMY48I factory images with Stagefright security patches for these devices last month.
Google rolled out OTA update for these devices for T-Mobile users earlier this week that was between 20MB and 30MB, so the OTA update should be available for these devices soon. This doesn’t change the Android version, so it remains the same at Android 5.1.1 that was released for Nexus devices back in May.
You can download factory images for these devices from the Google Developers website here. Google already confirmed at the Android M announcement that it will release the final version of Android 6.0 (Marshmallow) in Q3,2015, which is between July and September. We can expect the roll out for Nexus devices in coming weeks.