Checked http://www.ntg.nl/maps/36/16.pdf and http://www.tug.org/metapost/src/manual/mplibapi.pdf and not seeing a list of differences, and as @egreg noted, there shouldn't be any.
Posted the following:
\documentclass{standalone}
\usepackage{luamplib}
\begin{document}
%filecontents: parameters.txt
%a=100;
%b=133;
%t=6.35;
%m=12.35;
\begin{mplibcode}
beginfig(1);
input parameters.txt
draw (0, 0)--(b, 0)--(b, a)--(b, 0)--cycle;
endfig;
\end{mplibcode}
\end{document}
And it didn't work.
Turns out it didn't work due to a stupid error on my part (failed to consider that the two tools I'm trying to integrate use different characters for comments). Fixed (and my thanks to @egreg for proving it was my stupid error).
I would still like to know if there are any differences --- suspecting not, but the confirmation would be nice. Edited the title to reflect this, leaving the balance up as a monument to my stupidity. Re-edited, to make clear that it was entirely my mistake.
mpost
program is now just an interface to themplib
library.glyph
didn't work until a very recent build.show
goes to log only not to terminal.