Lately, in Debian Unstable, I have noticed package names starting to
appear with “t64” on the ends. No doubt this will percolate through to
Debian derivatives as well. I wondered what this was about, and found
this forum thread
<https://www.antixforum.com/forums/topic/t64-at-the-end-of-a-package-
title/>.

This has to do with the “year-2038” problem, which should only affect
32-bit systems anyway. But it seems some people are sufficiently
concerned about this to ensure that their code will build with a
64-bit size for time_t (the POSIX type for holding the number of
seconds since 1st January 1970), even on 32-bit systems.

This is controlled at build time by setting the _TIME_BITS symbol to
the value 64. There is a file /usr/include/features-time64.h (present
if you have the libc6-dev package installed) that does the necessary
setup of other time-related API calls based on this.

On 64-bit systems (which is what most of us would be running by now),
there would be absolutely no difference in the code with this setting.
So the change in package name is I think only to maintain
compatibility with 32-bit architectures.