The folks behind Chinese ePrice appear to have taken this promise to heart, for they have posted a video on YouTube where they subject the Xperia Z Ultra's screen to some rather extreme testing.
Luckily, a Stanley knife doesn't appear to register well enough with the phablet, so that precludes us from suggesting you consider a more sensible alternative that has your (future) phablet's longevity closer to heart. That being said, using your keys will work. And so will a coin or a pen. Actually, we'll just let you have a look for yourself, and see that Sony's promise mostly holds true.
The Sony Xperia Z Ultra is set for launch by the end of the month in Hong Kong, and as early as September 13 in the UK. Availability info is still sparse, but we'll let you know once we know more.
source: ePrice via XPERIA Blog