Claude Sonnet 4.5

Deprecated — retires 2026-11-30

Anthropic deprecated claude-sonnet-4-5-20250929 on 2026-09-30; retirement on the Claude API is 2026-11-30. Recommended replacement: claude-sonnet-5 (claude-sonnet-5-5). Released 2025-09-29; 200K context / 64K output.

Claude Sonnet 4.5

by Anthropic

Frontier foundation model optimized for agents, coding, and long-running tasks (Sonnet 4.5)

Part of the Anthropic Claude 4 series

See Anthropic release notes (Sept 29, 2025)

Summary

Sonnet 4.5 is Anthropic’s 2025 model release focused on safety, agentic workflows, and developer productivity. It’s positioned as a top coding and agent model with very large context capacity and improvements in alignment and safety.

Features

• Released: September 29, 2025
• Very large context window (reported ~200k tokens)
• Optimized for coding, agentic automation, and “computer use” tasks
• Strong domain knowledge improvements (coding, finance, cybersecurity)
• Built-in context-awareness and token-usage tracking (usage visibility during tool calls)
• Deployment across Claude.ai, Anthropic Developer Platform, Amazon Bedrock, Google Cloud (Vertex AI)

Superpowers

Sonnet 4.5 is best for teams building complex agents or doing deep-codebase work: long-running tasks, patching, multi-file refactors, and building autonomous agents. It reduces friction when working across large contexts and retains alignment improvements to lower safety risk in sensitive scenarios.

Pricing

• Token-based API pricing; discounts, promotions and enterprise pricing may apply. Current prices: see the vendor pricing page.

Safety & alignment

• Improved safety profile vs prior models (reductions in harmful behaviors in internal evals).
• Better handling of adversarial scenarios (blackmail, framing, sabotage) per Anthropic system card and evals.
• Designed for enterprise and internal deployment with strong monitoring and tooling.

Sources / notes:

• Anthropic Sonnet 4.5 release notes, system card, and third-party summaries.

Sources

• https://platform.claude.com/docs/en/about-claude/model-deprecations (accessed 2026-09-30)
• https://platform.claude.com/docs/en/models/overview (accessed 2026-09-30)