The HSPA+ only Chinese version of the Xperia Z1 Compact (M51w) is not yet widely on sale, yet it looks like users will see a day one update. A new firmware build with version number 14.2.A.1.146 started to roll for the handset according to the Untitled Xperia Team.
There doesn’t appear to be any noticeable changes from the recent global D5503 rollout with build 14.2.A.1.142. This ‘146’ build could be Chinese specific, stripping out Google apps and the like. A firmware FTF file is available to download here (password: 7jm7).