Here is quote from the xda-developers,

I GOT A REAL OFFICIAL 6.5 XPERIA ROM, YES, YOU READ CORRECT…OFFICIAL

The Build in the rom is a older 6.5..but what is important is:
-New XIP (real x1 nk)
-New OEM DRIVERS etc
-Some drivers from x2
-New netcf 3.7 (final)

I’m sure the cooked version will be available soon but not for the official one. I guess Sony Ericsson will have to wait for sometimes after the release of the Xperia X2 in October to let the X1 users to upgrade their device. But at least this is a good news for X1 users as well as the confirmed devices that will get a free and official Windows Mobile 6.5 update such as the HTC Touch Diamond2, Touch Pro2, and Snap, plus the Samsung Omnia II and Omnia II Pro B7610.

[Source]

The official new ROM update for Sony Ericsson Xperia X1 is now available. The update released on May 29 or earlier than expected which should be in June 2009. Unlike common Windows Mobile device, you have to use the Sony Ericsson Update Service software to get the ROM update file.

According to some source, the new update , R3A will make your Xperia X1 a better touch response, quicker media panel, better texting, brighter keyboard and a way for the handset to grab onto a stronger sigal. We know that before this update you can easily find the new ROM update through Xperia X1 forum or other sources. But with the official version it would be more safe and less risk to update your system. So, go get teh ROM update and tell us what changes happened to your Xperia X1.