They're not saying anything about Anthropic serving costs in that quote, just calculating what MTok price is for running agents. Next sentence after your quote:

> Agentic workloads have extremely high input-to-output ratios (our Claude Code usage has a ratio of about 300:1) and high cache hit rates (90%+). Because cached input tokens only cost $0.50/MTok, most of the tokens end up in the cheapest tier.

90% cache hit input blend: 0.9 * $0.5 + 0.1 * $5 = $0.95 per MTok.

300:1 input/output blend: (300 * $0.95 + $25) / 301 = $1.03 per MTok.

They don't say exact cache hit rate they calculated for ("90%+"), so close enough.