Given that there is a single species of human today and most of us have some percentage of Neanderthal DNA, it seems that we are one species today and we were also one species in the past (since we could and did interbreed)
That is tautologically true, considering how Neanderthal is an offshoot of Sapiens.
The question maybe worth asking is just how far they split off, compared to how far we are split off today (or maybe in the pre-modern era, I would expect us to be merging fast since then).
The question maybe worth asking is just how far they split off, compared to how far we are split off today (or maybe in the pre-modern era, I would expect us to be merging fast since then).