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Public story · 2026-07-25 · high
Ethan Mollick found Opus 5 strong on short tasks but weaker on long ones, even as Musk calls it frontier-tier.
Why now: Techmeme grouped these four reactions together in the July 25 briefing, and no consensus has formed yet on how good Opus 5 actually is.
Reactions to Opus 5 split fast, with four prominent voices in AI landing on different reads of the same model, per Techmeme's roundup.
For builders choosing a model, the split points to two different things to optimize for: peak capability, or reliability across a long task.
Musk grouped Opus 5 with Grok 4.5, calling the pair alone on the Pareto frontier. Aaron Levie called it a huge jump over Opus 4.8.
Ethan Mollick pushed back with something more specific. He found Opus 5 quirky: strong on shorter tasks, less ambitious once the work stretches out.
Bindu Reddy split the difference, ranking Opus 5 behind Fable in sheer brilliance but still a strict improvement over 4.8.
Mollick's read is the one worth acting on. If Opus 5's weak spot really is long-horizon ambition, the fix is in how you hand it work, not in waiting for a better model.
Harnesses that break a big goal into short, verified steps should get more out of Opus 5. Ones that hand it one open-ended task probably won't.
Give Opus 5 a genuinely open-ended, multi-day task and see if the quirky label holds. Nobody's run that test yet.
Each link below shares sources, entities, or timing with this story.
Opus built by Anthropic / Shared entities / Earlier coverage
Linked by a graph relationship (Opus built by Anthropic); both cover Grok, Musk, Opus; earlier Grok coverage from 2026-07-10.
Linked by a graph relationship (Opus built by Anthropic); both cover Fable, Grok, Opus; earlier Fable coverage from 2026-06-21.
Linked by a graph relationship (Opus built by Anthropic); both cover Ethan Mollick, Fable, Opus; earlier Ethan Mollick coverage from 2026-06-11.
Simon Willison uses Fable / Shared entities / Earlier coverage
Linked by a graph relationship (Simon Willison uses Fable); both cover Fable, Grok, Opus; earlier Fable coverage from 2026-07-17.
Opus built by Anthropic / Shared entities / Earlier coverage / Tension
Linked by a graph relationship (Opus built by Anthropic); both cover Grok, Opus; earlier Grok coverage from 2026-07-10.
Linked by a graph relationship (Opus built by Anthropic); both cover Fable, Opus; earlier Fable coverage from 2026-06-17.
Linked by a graph relationship (Opus built by Anthropic); both cover Fable, Opus; earlier Fable coverage from 2026-06-14.
Linked by a graph relationship (Opus built by Anthropic); both cover Grok, Opus; earlier Grok coverage from 2026-05-09.