If The Register is correct, the newest “Upgrade tool” will not offer a choice of not upgrading to W10.
“As the screenshot above shows, a new version of Microsoft's upgrade tool no longer offers the option of cancelling installation entirely. Instead, users are presented only with the choice of setting a date and time - being able to defer the Windows 10 installation by no more than a few days - or "start the upgrade now". The 'schedule your upgrade' window has no red X to allow users to close it, forcing them to pick one of those two options.” – Neowin
Mary Jo Foley, whose rep is solid. She’s been writing about MS for decades. She reports that the new pop up does not have a red X nor does it have any way to opt out of the Upgrade.
This will be especially bad news to the owners of Samsung devices. Samsung has not to date been able to update its drivers to W10.
The sources are linked above, the link for The Register shows the new no choice upgrade tool.
*Update - MS spokesperson stated that The Register report is inaccurate. Perhaps, but how does one show an "inaccurate" screen shot (short of altering an image)?