Anthropic: Claude Sonnet 4.5
Overview
Claude Sonnet 4.5 sets a new benchmark for AI-assisted development. It excels not only in code generation but also in building sophisticated autonomous agents, operating digital interfaces, and tackling complex reasoning and mathematical challenges.
Given that code underpins nearly every modern application—from spreadsheets to enterprise software—the ability to seamlessly interact with these tools and solve difficult problems is central to today’s workflows. Claude Sonnet 4.5 is engineered to meet that need.
Alongside the model release, we are rolling out a comprehensive set of product enhancements:
- In Claude Code, we’re introducing checkpoints, a long-requested feature that lets users save progress and revert to earlier states instantly. We’ve also revamped the terminal interface and launched a native VS Code extension.
- For the Claude API, we’ve added a context-editing capability and a memory tool, enabling longer-running agents and handling of more complex tasks.
- Within the Claude apps, code execution and file creation—including spreadsheets, presentations, and documents—are now integrated directly into the chat experience.
- For Chrome users, the Claude extension is now available to Max subscribers who joined the waitlist last month.
We’re also empowering developers with the same foundational tools that power Claude Code. This new offering, the Claude Agent SDK, provides the infrastructure behind our flagship products, giving you the flexibility to build at the frontier.
On safety and alignment, Claude Sonnet 4.5 represents our most aligned frontier model to date, with marked improvements across multiple alignment dimensions compared to previous versions.
The model is available starting today. Developers can access it via the Claude API using the model ID claude-sonnet-4-5, with pricing unchanged from Claude Sonnet 4 at $3 per million input tokens and $15 per million output tokens.
Usage example
curl https://www.namoclaw.ai/api/v1/chat/completions \
-H "Authorization: Bearer $API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "anthropic/claude-4.5-sonnet-20250929",
"messages": [{ "role": "user", "content": "Hello!" }]
}'Default parameters
| Name | Type | Default | Description |
|---|---|---|---|
| temperature | number | 1 | — |
| top_p | number | 1 | — |
| top_k | number | — | — |
| frequency_penalty | number | — | — |
| presence_penalty | number | — | — |
| repetition_penalty | number | — | — |
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