From a Microsoft email, sent out to companies and anyone subscribed to its quarterly 'lifecycle' newsletter, here are some selected lines of interest:
Microsoft provides industry-leading lifecycle policies – in length and provision – giving customers consistent, transparent, and predictable software support and servicing guidelines.
IMPORTANT: Security fixes are NO LONGER available for unsupported products. It is recommended to upgrade as soon as possible before this date.
On October 9, 2018 the following products will NO longer be supported:
• Windows 10 Mobile (released in Aug. 2016)
On June 11, 2019 the following products will NO longer be supported:
• Windows 10 Mobile (released in April 2017)
Which is as expected. Thus branch 1607 ('Anniversary Update'), first rolled out in August 2016, will cease to be supported as of Patch Tuesday in October this year, while the same will happen in June 2019 to branch 1703 ('Creators Update'), and so on.