Sony's new firmware update (v6.1288) finally brings HDMI 2.1 VRR and ALLM to X900H and XH90. Here are direct download links for Europe, North America, and other regions.
Update 6.10.2021: The update is now officially available from the
Sony UK support page and
Sony USA support page. It will also start rolling out over-the-air to your TV's built-in update function but it may take a while before it reaches all Sony X900H / XH90 TVs.
Update: In statements made to FlatpanelsHD Sony warns that the first VRR firmware is not final: "VRR has not been officially released for BRAVIA TVs. You can choose the VRR mode in the TV menu, but you may experience bugs. For the smoothest experience, we recommend waiting until VRR is officially released on BRAVIA TVs later this year," said Sony. The first update will be pushed out between October 6 and 13, and the second update for VRR will arrive later this year.
As for VRR on other models, Sony said: "The timing is still under consideration, but we can assure you that the update will arrive later this year."