Claude Sonnet 5.5 Is Now Live on Emergent
Claude Sonnet 5.5, Anthropic's newest Sonnet model, is now available on Emergent. You can select it when you start a new project. Anthropic released Sonnet 5.5 on September 28, 2026, and reports that it generates output more than 30% faster than Sonnet 5 while costing up to 30% less per task in its testing.
For builders, that puts a quicker, cheaper model next to Claude Opus 5.5 in your model picker. Opus 5.5 stays the choice for complex, open-ended work. Sonnet 5.5 is built for the everyday requests that make up most of a project.
How to use Sonnet 5.5 on Emergent
Choose Claude Sonnet 5.5 from the model selector in the prompt bar when you start a project. Model choice is set per project, so pick it before you describe your app.
Access runs through the Universal LLM Key, so there is no separate Anthropic account or API key to manage. Usage draws from your Emergent credits, the same way it does for every other supported model.
The rest of the flow is unchanged. Describe what you want in plain language, and the agent plans, builds, tests, and deploys the app from that conversation.
What Sonnet 5.5 brings to a build
Speed is the change most builders will notice first. Anthropic calls Sonnet 5.5 its fastest Sonnet model to date, and faster output shortens every step where you wait on the agent.
The lower cost comes from efficiency, not a price cut. Sonnet 5.5 keeps Sonnet 5's API pricing of $2 per million input tokens and $10 per million output tokens, but Anthropic says it needs far fewer tokens to finish the same work. Early testers also saw it batch tool calls together more often than Sonnet 5, which means fewer steps per task.
Anthropic positions the model for well-scoped everyday work: fixing bugs and producing polished documents, slides, and spreadsheets. It also credits Sonnet 5.5 with a sharp eye for design, and early testers noted the polish it adds to user interfaces. On a live app, that describes most of what you ask for after the first version ships.
Sonnet 5.5 nearly matches Opus 5.5 on coding benchmarks
Agentic coding shows the largest jump over Sonnet 5. The figures below come from Anthropic's launch post.
Terminal-Bench and CursorBench scores are vendor-reported by Anthropic; the Opus 5.5 Terminal-Bench figure is at Xhigh effort. GDPval-AA was run by Artificial Analysis on a pre-release Sonnet 5.5 deployment; Anthropic says a structured-output bug in that deployment, since fixed, may have slightly understated the score. Scores as of September 2026.
In Anthropic's published results, Sonnet 5.5 edges past Opus 5.5 on Terminal-Bench and lands about two points behind it on CursorBench. On GDPval-AA, the two models are nearly level, and Sonnet 5.5 sits roughly 400 points above its predecessor.
Anthropic is clear that benchmarks tell only part of the story. In its own testing and that of outside testers, Opus 5.5 remains clearly stronger at complex, open-ended work that needs sustained judgment.
When to pick Sonnet 5.5 over Opus 5.5
Pick Sonnet 5.5 when speed and cost matter more than deep reasoning. Iterating on a UI, fixing a bug, adding a form, or generating content inside your app all fit that profile.
Reach for Opus 5.5 when a build needs careful judgment across many moving parts, such as planning the data model and permissions for a multi-role business app. The API pricing reflects that split: Opus 5.5 lists at $4 per million input tokens and $20 per million output tokens, double the Sonnet 5.5 rates.
Anthropic says Claude Haiku 5.5, built for high-volume and cost-sensitive use, will join the 5.5 family in the coming weeks.
Build faster with Sonnet 5.5 today
Claude Sonnet 5.5 is in the Emergent model picker now. Select it at the start of your next project and put its speed to work on the everyday tasks that fill most of a build.
on Emergent today
