That's a big "if" - Joomla have missed every deadline they've ever set for J4 for the past 3 years.
But... First of all we're not going to make Gantry 4 or any of it's templates compatible with Joomla 4. However, at the time, they release J4 they will also release J3.10.x which will be supported (by Joomla) for a further two years, so that removes some of the pressure to update.
For Gantry 5, it's still out intention to make Gantry 5 compatible with J4. In fact, there's already a test Gantry 5.5 version that is starting to do much of the groundwork that needs testing if you want to help
https://rockettheme.com/forum/announcements-all/286608-gantry-5-5-testing-needed
. I stress though that this is a TEST version and should not be used on production sites. Once, J4 is released we will continue final work on releasing a version of Gantry 5 that is compatible (but this won't be straight away - it will take some time). After that, it's likely that ALL the Gantry 5 templates will need an update too - again this will take us time.
So, sorry but I can't give you any timescales really - we're a smaller team than we once were and innevitably with such a large portfolio for us to maintain and support Joomla 4 templates will take us some time to release.
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