Manual upgrade/migration from OH2 to OH3

I use runtime/bin/update to upgrade OH2 (I run OH2 on gentoo with java 1.8).
for example, I just did a
runtime/bin/update 2.5.11
Can I use runtime/bin/update to upgrade from OH2 to OH3 as well (I will switch to java 11 too)?

What is the content of your file called update ?
I am on an other linux and the content just shows a hint to use the systems package manager to do updates.
The OH2 and OH3 packages have different names ( openhab2 vs. openhab ).
So it is not just an update.
Have a look to Guide: Installing and testing OH3 snapshots/milestones using APT and YUM it explains the most important things.

@Wolfgang_S Thanks for reply and link to OH3 install guide

runtime/bin/update is a shell script and its content is the one provided by openhab repository itself (in openhab home directory, i.e. /opt/openhab2/runtime/bin/update in my case and from 2.5.11 git tag).

gentoo does not have rpm or apt package manager commands (gentoo builds everything from source) so it needs manual openhab install method and manual openhab upgrade method (in /opt). install and upgrade work perfectly fine for OH2 in gentoo.

So now I wonder if the update script does, or will, support upgrade from OH2 to OH3. Or, perhaps, update script will never support upgrade from OH2 to OH3?

update for now I test run OH3 in a minimal ubuntu chroot inside gentoo