Microsoft launched the developer preview version of its first major Windows Phone 8.1 update on Aug. 4, though HTC 8X users were unable to download and install it. That problem will persist for at least another month, as HTC says it won't come to the 8X until "late October."
In a response to a question on Twitter, the official HTC account said users "can expect the Windows 8.1 update to roll out to Verizon's HTC 8X in late October," though an exact release date wasn't provided. HTC also didn't provide any estimate on when AT&T, T-Mobile and other service provider users can expect the update.
Given that phones are now coming with the update preinstalled, it's likely all devices and carriers will begin receiving the upgrade sometime around October. The update will likely be one of the last significant releases for Windows Phone before Microsoft transitions its mobile devices to the next version of Windows, which will have an SKU specifically for tablets and phones.