Install this version:
emerge -a =www-misc/open-webui-0.9.6
If this version is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask
emerge
autounmask =www-misc/open-webui-0.9.6
Or alternatively:
emerge --autounmask-write -a =www-misc/open-webui-0.9.6
open-webui-9999.ebuild