Android M will reportedly bring some notable changes to the Nexus update policy, but it will also mean some older models will not go past Lollipop.

While Android 5.0 was a major change mostly in terms of visual experience, the upcoming Android M will bring changes in other departments. With the next version of Google's popular mobile operating system, some older Nexus devices will remain on Lollipop, while others will benefit from a new update guarantee along with Android M.

More specifically, this update guarantee will ensure that Nexus devices get major system updates for two years and security patches for three years from the availability of the OS, or at least 18 months from the date of purchase (whichever lasts longer). The news comes from Android Police, which seems fairly confident in its sources and the accuracy of this information.

"We're rating the update scheme as a 9 on the confidence scale. Our sources on this are solid, so we believe it will be announced at some point before Android M hits devices, but the I/O keynote would be a good time," notes the publication, while also adding that nothing is reall certain.

The report further reveals that these rules will apply to older Nexus devices as well, not just new ones, albeit it means that some of them will reach the end of the line. According to the publication, the older Nexus 4, Nexus 10, and original Nexus 7, all of which came out in 2012, will get security patches for a little while longer, but will not get Android M. Moreover, the 2012 Nexus 7 is "at the very end of its rope."

"The N4 and N10 came out in November of 2012, so they're well past the two year OS cutoff. The Nexus 4 was out of the Play Store in fall of 2013, so the three year security patch cutoff will be observed for this phone. That means this fall will be the end of N4 support. The Nexus 10 was sold for much longer, only dropping out of the Play Store in fall 2014 (along with the 2013 N7). So in this case it will have security updates through early 2016. The 2012 N7 wasn't nearly as long-lived as those devices. It came out in the summer of 2012 and was dropped about a year later. It's already past the major update limit (I guess Google was feeling nice with Lollipop), but this summer is the end of security patches," Android Police further explains.

The 2013 Nexus 7, meanwhile, should continue to receive system updates until later this summer, and security patches until next summer. The Nexus 5 will be in virtually the same situation, while the new Nexus 6 and Nexus 9 will receive system updates at least until the fall of 2016, and security updates a while after that.

It remains unclear at this point whether Google will announce these update guarantees at its upcoming I/O developer conference or wait until later in the year to unveil the new Android M along new Nexus hardware. None of this is confirmed for now, so it's best to take this news with a hefty grain of salt.