Claude Sonnet 4.5 Launches With A Surprise Experiment: The AI Can Generate The App You Want On The Fly

Anthropic on Monday unveiled its next-generation AI model, Claude Sonnet 4.5, calling it the "best coding model in the world." The AI firm says its new model is "the best model at using computers," and shows significant improvements in reasoning and math. Claude Sonnet 4.5 tops several benchmark tests, with Anthropic saying the AI can maintain focus for more than 30 hours on complex tasks, compared to seven hours for Opus 4.

The AI's computer use abilities have also improved compared to Sonnet 4, with Anthropic making the Claude for Chrome extension more widely available. The tool lets the AI perform actions on behalf of the user,. Claude Sonnet 4.5 is also safer, with the company saying the model is its most aligned ever, featuring reduced "concerning behaviors," like "sycophancy, deception, power-seeking, and the tendency to encourage delusional thinking."

Anthropic

If that's not enough to indicate how big an upgrade Claude Sonnet 4.5 is, you should know the new AI model is the only one in Anthropic's history that was able to create a working version of the Claude website, according to a demo. A new "Imagine with Claude" feature is even more exciting, though the feature is available only in preview to Max subscribers. Imagine with Claude lets the AI generate code on the fly, without taking into account prewritten code or functionality. Instead, Claude creates in real-time, responding to what the user is doing.

An Anthropic demo shows Claude responding to a prompt that says: "Imagine William Shakespeare's computer." The AI went to work, deploying an interactive user interface for a computer Shakespeare would have used. It's effectively an on-demand app that opens inside Claude, letting the user interact with it. Claude doesn't write the code in advance; it waits for the user to interact with it. When the user clicks a menu item, Claude generates that code on the fly, allowing the user to actually browse Shakespeare's computer in real-time (images above and below). Anthropic describes it as software that generates itself in response to what you need, indicating that apps in the future might not be premade, but they'll be able to respond to exactly what the user needs. 

Anthropic

As exciting as "Imagine with Claude" might be, that's a feature only Max users will have access to, and something they won't necessarily use on a regular basis. Claude Sonnet 4.5 has plenty of finished features that users can take advantage of right away. Anthropic says that experts in various fields, including finance, law, medicine, and STEM, found that Claude Sonnet 4.5 is "dramatically better in domain-specific knowledge and reasoning" compared to previous models.

Anthropic

Claude Code now supports checkpoints that let users save their progress and roll back to a previous state. Claude agents can run even longer when working on more complex tasks. Anthropic also brought support for code execution and file creation (documents, spreadsheets, and slides) to Claude conversations (image above).

A different demo showed that Claude for Chrome can easily navigate apps like Google Docs and Gmail inside the Chrome browser, collect information, create and update documents, and send emails on behalf of the user if it has the permission to do it (image above).

Claude Sonnet 4.5 will be available to users in Claude apps, the Claude API, and Claude Code. For developers, pricing remains unchanged from Claude 4, at $3/$15 per million tokens. A new Claude Agent SDK is available to developers. Anthropic explains that the new SDK represents the building blocks that allowed the company to develop Claude Code. The new Claude Agent SDK will let developers create their own AI agents in addition to helping with other coding projects.

Anthropic

In addition to rolling out the new model, Anthropic also expanded access to previous Claude features that were reserved for specific subscription tiers. Claude's file creation tool is now available to all paid users, after launching to Max subscribers a few weeks ago. The Claude for Chrome extension is also expanding access to more users, as long as they are on the waitlist. The feature launched in late August, with Claude Max users being the first to get access to this computer use model. That's when Anthropic started a waitlist for users without access.