It's understood that JoomSEF v.4 is compatible with Joomla CMS 2.5 (according to other existing forum topics) ...

Before we order JoomSEF 4 we need to be clear that no additional Joomsef versions are planned to be released for Joomla 2.5 and that v.4 will have continued support for CMS 2.5 going forward.

We do not want to order v.4 and then get stuck having to order a new version again after a surprise release.

Hi,
I can't promise that for future, but so far it seems that JoomSEF 4 is fully compatible with Joomla 2.5, so we don't plan to release a separate version of JoomSEF for it.

Also, according to joomla.org: "Version 1.7 will reach end of life on 24 February 2012." So if there's some incompatibility, it's most likely that instead of releasing a separate version, we'll adapt JoomSEF 4 to support 2.5 only.