DragonBasic

Those are all disassemblies, not the original code (although the original code for 6809 BASIC was recently found, see https://github.com/davidlinsley/DragonBasic). Similarly, the blog post links a version of 6502 BASIC by Michael Steil on Github that's set up to build the BASIC ROMs for a variety of computers, but that appears to be based on a disassembly rather than the original code as well. Here's a random bit of code (the code handling processing a FOR statement) from Microsoft's repo, vs. the same code from Steil's repo: https://github.com/microsoft/BASIC-M6502/blob/main/m6502.asm... https://github.com/mist64/msbasic/blob/master/flow1.s#L3

Fun fact, GW-BASIC was a descendant of the original Altair BASIC. The "Translation created 10-Feb-83" headers on each source file refer to tooling Microsoft had that automatically translated the 8080 assembly to 8086 (it shouldn't be taken as a build date since they were manually modified after that point). Besides GW-BASIC, source code for the 6502 and 6809 rewrites of Microsoft BASIC were available up to this point (see https://www.pagetable.com/?p=774 and https://github.com/davidlinsley/DragonBasic) but I believe this is the first public release of the original 8080 BASIC code.