Composer 2.5 is 1T total/32B active (based on Kimi 2.5), while Elon publicly said Grok 4.5 is 1.5T parameters total. Hardly a different weight class.

The API cost difference is ~2.5x, probably because xAI has much higher costs to recoup.

I could easily see Grok 4.5 being around 1:16 in terms of active parameters, so around 94B active parameters.