Thanks to the developer behind LineageOS, Samsung Galaxy Tab S3 users are able to get Android 8.1 Oreo on their tablets. This is a third party ROM, so you will need to have TWRP custom recovery installed in order to install custom ROM, like this one.
Here is how to install it on your Tab S3:
1. Install twrp for Tab S3.
2. Download the zip(s) – firmware and Google Apps additional package (http://opengapps.org/, Platform: ARM64, Android: 8.1, Variant: any, usually I’m using micro or nano)
3. Backup all partitions (it least efs) and store somewhere – it need to do – because you can loose imei
4. Full wipe all
5. Flash firmware and gapps
Keep in mind that microphone is not working during calls but who uses their tablet for making calls? Other than that, everything is working like a charm.
Again, this is a custom ROM for Samsung Galaxy Tab S3 and after installing it, your warranty will be voided. Unfortunately, this is the only way to get latest Android on your tablet as Samsung appears to be reluctant in pushing any more updates to this tablet.