However, at my previous job I integrated an LFBGS[1] implementation into our production code.

That was written in the early 80s in Fortran '77.

The code outlived all hardware that it ran on when it was first written (we ran it on an OpenMP cluster for a scientific-computing problem related to lithographic mask optimization), if not its authors.

It will continue to exist, and run, for a very long time.

Sure, all software is ephemeral. But as you say so, you probably used SciPy/NumPy. Deep inside, there's an implementation of LAPACK/BLAS doing the heavy lifting for you[2]. It started in 1979, and is still kicking.

(And it's still in FORTRAN)

[1]https://en.wikipedia.org/wiki/Limited-memory_BFGS

[2]https://en.wikipedia.org/wiki/Basic_Linear_Algebra_Subprogra...