Anthropic released Claude Sonnet 5 on Tuesday, calling it "the most agentic Sonnet model yet." It's the default model for Free and Pro users, live on Max, Team, and Enterprise plans, in Claude Code, and through the API . Unlike past Sonnet launches, this one is built to sit next to the previous Opus instead of trailing a tier behind it.
On SWE-bench Pro—a coding benchmark pulling problems from actively maintained repositories with multi-file changes, scored as percent solved—Sonnet 5 hit 63.2% against Sonnet 4.6's 58.1%.
On GDPval-AA v2, an Artificial Analysis benchmark that scores real-world professional tasks across 44 jobs via blind pairwise Elo ratings, it landed at 1,618, a statistical tie with Opus 4.8's 1,616. The differences between Sonnet 5 and Opus 4.8 on Humanity's Last Exam are basically negligible: 57.4% vs 57.9%.
Sonnet 5 also ships with an updated tokenizer—the system that breaks text into the units a model bills for—and it's hungrier, turning the same input into a task that consumes more tokens. “Sonnet 5 is an upgrade to Sonnet 4.6, but it uses an updated tokenizer that changes how the model processes text to improve performance” Anthropic wrote in a small footnote. “The tradeoff is that the same input can map to more tokens: roughly 1.0–1.35× depending on the content type.”
Anthropic set the $2/$10 introductory rate to make that switch close to cost-neutral through August 31, after which price reverts to the standard $3/$15 Sonnet has charged.
Our typing game ran on the first try, with cleaner visuals and tighter logic than Sonnet 4.6 produced on the same prompt.
However, it took way too much time compared to other models (roughly 30 minutes of reasoning) and consumes tokens like crazy. That single iteration ate 90% of our 5 limit quota on the Claude Pro plan.
On a harder multi-step coding task, Sonnet 5 landed close to Opus 4.8 depending on effort level, and the same prompt run multi-shot cost noticeably less than the equivalent job on Opus or Fable.
That said the generational gap won’t feel as impressive as the jump from Claude 3 to Claude 4, for example. Also a sign on how big AI companies are rushing to release new models, no matter how big the improvement is.
Going by that optimistic cadence, Haiku 5 and Opus 5 are the two models still due, potentially to be released this year. That said, Anthropic hasn’t been consistent with releases. The gap between Haiku 4.5 and Sonnet 4.6 was more than 3 months, so keep your fingers crossed if you want to test Opus 5 soon.
