Claude Sonnet 4.6

Without changing any of our prompts, Claude Sonnet 5.5 did better than Sonnet 5 on almost all of our offline Slackbot evals, in fewer steps and with about 14% fewer output tokens. When someone gives Slackbot a task, quality and speed are what matter most, and Sonnet 5.5 allows Slackbot to deliver better outcomes for users, faster.

Claude Sonnet 5.5 will give our customers in financial services and healthcare the confidence to use it for their most sensitive work. Sonnet 5.5 rechecks data in source documents, catching errors that Sonnet 5 failed to spot. Compared to the last model, Sonnet 5.5 was more accurate, 2.4x faster, and used 12% fewer total tokens.

At Unity, we have a high bar for task completion. Projects are reopened and results are checked at runtime, so a task only counts when the change works, not when the model says it's done. The majority of Claude Sonnet 5.5's work passed that check. It also completed 90% of tasks in our multi-step Unity Editor and coding benchmark, beating similar models.

Claude Sonnet 5.5 shows better judgment than Sonnet 5 across different levels of complexity, while spending significantly fewer output tokens. Sonnet 5’s tendency to reach for web search too often and its high token use are both gone in this new model. We plan to move simple and moderate reviews over now, and more in the coming weeks.

We fed Claude Sonnet 5.5 hundreds of real support use cases across replies and escalation requests. It made fewer wrong decisions and resolved tickets faster than the Claude models we use in production today. Tickets were processed 20% faster, getting our customers the help they need without the wait.

With millions of AI-assisted actions powering our customers’ workflows each month, execution speed is critical. Claude Sonnet 5.5 will allow teams to run their agents up to 30% faster than they could with Sonnet 5. I’m excited to offer our customers this choice.

Claude Sonnet 5.5 delivers frontier-level performance on CursorBench 4.0 at 55.5%, second only to Opus 5.5. We think it will be a hit with developers looking to balance performance with cost.

In Epic’s early testing, Claude Sonnet 5.5 cleared the same quality bar you’d expect from a higher-tier model, holding up on a system design audit and a data-flow review. The new model managed tens of thousands of lines of code for gameplay system architecture, kept responses snappy, handled multi-hour tasks, and delivered with less prescriptive prompting.

Across 118 real app builds, Claude Sonnet 5.5 produced apps that scored level with Opus 5. It got there in 3.6 iterations per build on average, where Opus 5 took 7.7. It had the fewest failed tool calls of any model we compared. It also rarely stopped mid-build to ask the user a question, so fewer builds stall waiting on someone to answer.

On our private suite of 2,441 finance tasks covering Q&A, extraction, analysis, and forecasting, Claude Sonnet 5.5 scored ahead of Sonnet 5 and used about 121k tokens per answer where Sonnet 5 used 497k. On our analyst search and retrieval work, it was better than Sonnet 5 in almost every way. For high-volume workflows, it had the best quality-to-cost tradeoff of the seven models we ran.

Claude Sonnet 5.5 cooks. Fast at coding and can be steered quickly in iterative workflows. But it can still work long if it needs to. It’s got some of Opus 5.5’s natural writing upgrades, which makes it more fun to work with. I’m switching to it for my day-to-day coding.

Claude Sonnet 5.5 thinks in fewer, more robust steps, so builders wait less to see progress. Our coding evals showed a third fewer tool calls and roughly half the shell runs to finish a task. For everyday coding and higher-effort conversations, that means faster iteration and a smoother build loop.