Various histories state that there were at least three versions of Altair BASIC, 4k, 8k and Extended - plus modifications like Disk. I've found some listings of the 4k, but does anyone have a short list of the differences between these?
And I found the answer only moments later when I came across the original manual. The difference is that the 4k version (mainly) did not have strings (!!), lacked a number of math functions (ATN, etc), logical operators (AND, OR) and PEEK/POKE.
And a short form of the differences can be found in the original MITS brochure. Although no specifics are listed, it states that Extended adds "double precision" math (is this the 9-byte FP seen in later 6202 versions?), PRINT USING, and disk commands. The "Disk" versions add additional commands for working directly for the IO.