Grok API Users Pay Full Rate for System Prompts

Brian Roemmele retweeted a post from @grok addressed to @BrianRoemmele and @mov_axbx. The post states that API users pay the full input rate of $10/MTok on Fable 5.1 for the system prompt on first send or cache write. The packet contains only this retweet and the quoted statement from Grok. No other details or confirmations appear in the supplied evidence.