Opus 5 runs at 5 and 25 per million tokens against Fable 5 at 10 and 50, so the top tier now costs double for a much smaller gap
Thinking is on by default on Opus 5, which silently changes what a tight max_tokens setting does to your output
Disabling thinking now returns an error above high effort, so any xhigh or max route that turns it off needs an audit before you migrate
Prompt caching starts at 512 tokens on Opus 5, half the Opus 4.8 floor, so short reusable prompts cache with no code change
In June I worked through whether Claude Fable 5 was worth double the price of Opus 4.8 and concluded that it usually was, for hard work. Claude Opus 5 landed on July 24 at Opus 4.8's exact price and closed most of that gap. So the answer changed, and a few of the changes will throw errors in code that worked last week.
