No, I've just seen benchmarks showing most models start degrading around 4-5 bits. That's not to say they become useless, just that down to about 6-bits (with careful hybrid quantizations like unsloth where some of the layers aren't quantized or are quantized at higher bit depths) the quality isn't measurably degraded, but below that there are measurable differences in performance.

People report good results from DeepSeek V4 Flash at 2 bits (the DwarfStar 4 folks are doing it, and I've tried it on my Strix Halo, but it's too slow to be usable, so I haven't bothered to figure out if it's actually smart enough to use for anything).

Anyway, it's obvious models have to degrade in terms of knowledge, at any quantization, even though it may not show up clearly on benchmarks until lower. If you halve the size of the data available, it necessarily loses information about the world.