Anthropic launches Claude Sonnet 4.5, its best AI model for coding

On Monday, Anthropic launched a new frontier model called Claude Sonnet 4.5, which it claims to offer state-of-the-art performance on coding benchmarks. The company says Claude Sonnet 4.5 is capable of building “production-ready” applications, rather than just prototypes, representing a leap in reliability from previous AI models.

Claude Sonnet 4.5 will be available via the Claude API and in the Claude chatbot. The pricing for developers is the same as Claude Sonnet 4: $3 per million input tokens (roughly 750,000 words, or more than the entire Lord of The Rings series) and $15 per million output tokens.

In the last year, Anthropic’s AI models have emerged as a favorite among developers and enterprises, in large part due to their strong performance on software engineering tasks. Apple and Meta reportedly use Claude AI models internally, and Anthropic has made a significant business selling API access to AI coding applications such as Cursor, Windsurf, and Replit. Recently, OpenAI’s GPT-5 has challenged Anthropic’s dominance in the space, outperforming Claude models on a variety of coding benchmarks.

Anthropic says Claude Sonnet 4.5 offers industry-leading performance on several coding benchmarks, including SWE-Bench Verified. However, Anthropic AI researcher David Hershey tells TechCrunch that it is hard to capture Claude Sonnet 4.5’s performance on benchmarks alone.

Hershey says he’s seen Claude Sonnet 4.5 code autonomously for up to 30 hours during early trials with some enterprise customers. In that time, he watched the AI model not only build an application, but stand up database services, purchase domain names, and perform a SOC 2 audit to make sure the product was secure.

In a statement shared with TechCrunch Cursor CEO Micheal Truell said Claude Sonnet 4.5 represents state-of-the-art coding performance, specifically on longer horizon tasks. Windsurf CEO Jeff Wang said in a statement that Claude Sonnet 4.5 represents a “new generation of coding models.”

Anthropic also claims that Claude Sonnet 4.5 is its most aligned frontier AI model yet, with lower rates of sycophancy and deception than previous models. The company says it has also improved Claude’s susceptibility to prompt injection attacks.

Alongside the launch of Claude Sonnet 4.5, Anthropic is also launching the Claude Agent SDK. The company says this is the same infrastructure that powers Claude Code, and can be used to help developers build their own agents.

Anthropic is also releasing a temporary research preview called “Imagine with Claude” for Max subscribers, which shows the AI model generating software on the fly. The company says the model will respond to user requests in real time, with no predetermined functionality or prewritten code.

The tense competition in the AI world has made it common for companies to ship flagship models every few months. Claude Sonnet 4.5 is launching less than two months after Anthropic’s last AI model, Claude Opus 4.1. These rapid production cycles make it difficult for any company to hold a meaningful lead for very long.