Safari Technology Preview is the version of the Apple browser that you use to experiment with new features. It is a version of Safari that is in constant beta, and its many features, some come to the main version of Safari for macOS.
Given the many changes that are in the web development every day, Apple updates every two weeks Safari Technology Preview. And sometimes, it also updates due to security problems.
Although Safari for macOS has already been updated a few days ago to avoid the Specter vulnerability (or at least mitigate it), now Apple has also updated Safari Technology Preview to patch this vulnerability.
The version of Safari Technology Preview 47, in particular, is the one that already has this patch. To update we can do it right from the Mac App Store, either by downloading the latest version from the Apple page.
Remember that the Specter vulnerability appeared next to Meltdown and occurs on virtually every computer in the world that has an ARM, AMD or Intel chip. At the time we explained how it affects Apple and how the company has already patched it in a certain way on their devices.
In a certain sense because even though Meltdown can be completely patched, Specter can only be patched to mitigate the damage. Of course, making an attack on Specter is very complicated and with the latest updates, there is almost no need to worry more.
So, the only thing you should do is update your devices to the latest available version. Both operating system and browsers and apps like Safari Technology Preview.
In any case, keep in mind that Safari Technology Preview is a version focused on developers and web designers who need to test the latest web standards, so maybe you should be using Safari in its normal version.