Claude 4 Opus Launches with Extended Thinking
Anthropic's new flagship model adds a 'thinking' mode that visibly reasons through problems before answering. We tested it on long-form coding, planning, and research tasks.
Staff7 min read
Anthropic's new flagship model adds a 'thinking' mode that visibly reasons through problems before answering. We tested it on long-form coding, planning, and research tasks.
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Anthropic released Claude 4 Opus this morning, and the headline feature isn't a benchmark — it's the model's new ability to *think out loud* before answering. Hit a complex enough question and the model now shows its reasoning, sometimes for thirty seconds or more, before producing a response.
We've been testing it for the past 48 hours on the kinds of tasks where prior models fall apart: refactoring a 4,000-line legacy codebase, planning a six-week product launch, and walking through scientific papers we don't have the background to evaluate independently. The pattern is consistent: extended thinking helps most when the right answer requires holding multiple constraints in mind at once.
The clearest wins are in tasks where the failure mode of prior models was confident-but-wrong. Asked to design a database migration that preserves backward compatibility, Opus 4 will now spend 20+ seconds visibly considering edge cases — partial deploys, in-flight transactions, stale read replicas — before producing a plan. The plan it produces is materially more careful than what came out of Sonnet 3.7 on identical inputs.
The model now shows its reasoning, sometimes for thirty seconds or more, before producing a response.
For simple lookups, summarizations, or single-step transforms, extended thinking just adds latency. The product makes the right call here — a routing layer in the API decides whether thinking is needed, and skips it for obvious cases. You can also force-enable or force-disable per request.
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