TL;DR: Any official version of AutoHotkey released within the past six years is based on AutoHotkey_L.
AutoHotkey Basic refers to AutoHotkey 1.0, while AutoHotkey_L refers to AutoHotkey 1.1
This is confirmed on the AutoHotkey download page:
- AutoHotkey 1.1.* - previously known as AutoHotkey_L.
- AutoHotkey 1.0.* - also retroactively known as AutoHotkey Basic, Classic, Vanilla, etc.
- AutoHotkey 2.0-a* - see AutoHotkey v2.
Source: AutoHotkey: Downloads
AutoHotkey_L was originally a fork of Autohotkey created by Lexicos. To distinguish between the original AHK and Lexicos's fork, users began referring to them as AHK_Basic and AHK_L respectively.
AHK_L was at one time a very popular fork of AHK, and when AHK's
creator began to lose interest in maintaining the official branch many
people called for AHK_L to be designated as the official branch of the
program.
It took some years to decide to make AHK_L the official
branch, so in the meantime users here coined the terms "AHK Basic" and
"AHK_L" to help users distinguish between the different versions. But
since AHK_L is now the official branch, it is AHK and there's no need
to distinguish.
Source: Post by sinkface on AHK_Basic vs. AHK_L, what's the difference?
AutoHotkey_L was made the official branch of AutoHotkey in 2012. The source code can be found at https://github.com/Lexikos/AutoHotkey_L
If you're curious, the source code for AutoHotkey Basic (1.0.x) is publicly available on GitHub. The last non-readme update for AHK Basic was made on September 25, 2009. (v1.0.48.05).