Can you give some examples of what you're referring to? Practical AD is generally a pretty new thing, especially as a built in construct like in Jax of Flux.jl

Can you give some examples of what you're referring to? Practical AD is generally a pretty new thing, especially as a built in construct like in Jax of Flux.jl / zygote (maybe swift?). Also tapenade that I've never used but I think works to differentiate C code. There is also something called enzyme that implements automatic differentiation within LLVM IR which sounds super cool but is over my head unfortunately. But all this is very new stuff (tapenade is the oldest on my list I think). What languages from the early 2000s do you mean?