GTA San Andreas was initially released on the Xbox 360 back in 2008. However, that was a straight port of the Xbox Original edition. The new remake replacing that port on Xbox Live features 720p resolution with enhanced draw distance. It also includes the following Achievements (via Rockstar Support):
If you bought the Xbox Originals version of GTA San Andreas, you'll still be able to access it. However, if you want to access the new features of the remake, you have to buy it. Furthermore, your save files from the Xbox Originals San Andreas won't carry over to the new version.
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