Both apps have offered usage for free for a limited time:
https://blog.kilocode.ai/p/grok-code-fast-get-this-frontier-...
If xAI in particular is in the mood to light cash on fire promoting their new model, you'll see it everywhere during the promo period, so not surprised that heavily boosts xAI stats. The mystery codename models of the week are a bit easier to miss.
Also cheap enough to not really matter.
A bad model with good automated tooling and prompts will beat a good model without them, and if your goal is to build good tooling and prompts you need a tighter iteration loop.
I would rather use a model that is good than a model that is free, but different people have different priorities.
Y'know with all these latest models, the lines are kinda blurry actually. The definition of "good" is being foggy.
So it might as well be free as the definition of money is clear as crystal.
I also used it for some time to test on something really really niche like building telegram bot in cloudflare workers and grok-4-fast was kinda decent on that for the most part actually. So that's nice.