Is there something specifically with Kimi that's better here? As far as I know Kimi pricing is about the same as Sonnet 5 -- what happens if you use that model and Fable instead? Or Grok 4.5 which is even cheaper?

The article says Kimi is better at some things than Fable. That's probably not true of Sonnet.

One benefit of an open source one is that you can, as a large corporation, run it "locally" within your own data center. Even fine tune it.