The (optimistic?) take is that xAI is genuinely better at building datacenters at scale than anyone else, and the freedom to use Nat Gas as the primary energy source allows them to have lower marginal costs.
The (pessimistic?) take is that they have loads of idle GPUs and want to get some revenue out of them rather than none. Compare this to OpenAI/Anthropic where every token used by a consumer has to compete with enterprise spenders, and there’s not enough to go around for everyone.
It's also sensible for them to provide a cheap, intelligent model to users if they have capacity, then once they built a user base, tighten the screws. All the other AI providers have done that.