- DOWNLOAD: Android 2.3.7 (GWK74) For Sprint Nexus S 4G (Mirror)
- Rename the file to "update.zip" (please make sure you have file extensions set to show)
- Place it on the root of your SD card (not in a folder)
- Reboot into recovery
- Select "Apply update.zip"
If you are running a custom ROM and want to flash to the stock GWK74 update, check out this thread over at XDA. There are links for both de-odexed and odexed versions.
Google+, Thanks Omar!