Anthropic Introduces Claude Sonnet 4.5 and Claude Agent SDK

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Anthropic has released Claude Sonnet 4.5, delivering significant improvements in software engineering, multi-step agent reasoning, and autonomous computer use. The release is accompanied by developer tools including the Claude Agent SDK and checkpoints for Claude Code.

Key points

  1. Claude Sonnet 4.5 achieves 77.2% on SWE-bench Verified and 61.4% on the OSWorld computer-use benchmark.
  2. Pricing remains unchanged from Sonnet 4 at $3 per million input tokens and $15 per million output tokens.
  3. Claude Code gains a rollback checkpoint system, an updated terminal UI, and a native VS Code extension.
  4. The Claude API adds context editing capabilities and a memory tool to handle longer, more complex agent tasks.
  5. The new Claude Agent SDK exposes the underlying infrastructure of Claude Code for custom agent development.
  6. Claude apps add direct code execution and document generation, running under AI Safety Level 3 (ASL-3) protections.

Why it matters

For software engineers and businesses, Sonnet 4.5 provides major capability leaps in autonomous long-horizon programming tasks at no extra cost. By releasing the Claude Agent SDK alongside IDE tooling, Anthropic provides building blocks for production-grade agentic workflows.

Analysis

Anthropic continues to lead in coding benchmarks and agent orchestration. The model's demonstrated capacity to sustain focus across multi-step tasks for over 30 hours, paired with parallel tool execution and memory primitives, establishes Sonnet 4.5 as a drop-in replacement tailored for production engineering environments.

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Summary generated by AI (Gemini 3.8 Flash, 27 September 2026). It may contain errors – the original source is authoritative.

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