Both Ends of the AI Frontier Moved in One Week

Last week I wrote about open source models as a more affordable path compared to frontier commercial models, and the big question of when they’ll be good enough.

This week we have fresh evidence that the commercial frontier is moving extremely fast (which usually means open source will follow).

Sonnet 5 is now competitive with Opus 4.8 on many agentic and reasoning tasks, but at significantly lower cost. Meanwhile, Fable 5 has taken the top spot on the leaderboard. It’s clearly more capable than Opus 4.8 across complex coding, agentic workflows, and knowledge work, but it currently costs roughly 2x as much.

So the pattern continues: new capability levels get unlocked at the frontier (at premium prices), then the economics shift as smarter, cheaper options become available. We just saw both ends of that spectrum move in the same week.

I’m genuinely excited for the day when Fable-level intelligence becomes economically accessible for most use cases. Can we just fast forward now please?

Buckle up!