Comment by fastball

Output tokens are 5x more expensive than input tokens, so I'm not sure "dominate" is entirely correct.

A conversation with 20 turns, 50k tok growth per turn, 1m tok context at end would price out like this:

Fable 5 ($1/M cache reads) ; cache reads 9.5M tok × $1.00 = $9.50 ; cache writes 1M tok × $12.50 = $12.50 ; output 1M tok × $50 = $50.00 ; total = $72.00

Fable 5.1 ($0.25/M cache reads) ; cache reads 9.5M tok × $0.25 = $2.38 ; cache writes 1M tok × $12.50 = $12.50 ; output 1M tok × $50 = $50.00 ; total = $64.88

So yes, cheaper, but not massively.