How *exactly* is Deepseek so cheap?

Deepseek's all the rage. I get it, 95-97% reduction in costs.

How *exactly*?

Aside from cheaper training (not doing RLHF), quantization, and caching (semantic input HTTP caching I guess?), where's the reduction coming from?

This can't be all, because supposedly R1 isn't quantized. Right?

Is it subsidized? Is OpenAI/Anthropic just...charging too much? What's the deal?