Claude Sonnet 5 Release Notes

Claude Sonnet 5 enhances agentic capabilities and tool use

Claude Sonnet 5 被设计为 Sonnet 系列中最具代理能力（agentic）的模型，使其能够制定计划、利用浏览器和终端，并自主运行。它显著缩小了 Sonnet 级模型与 Opus 级模型之间的性能差距，在保持较低成本结构的同时，提供了接近 Opus 4.8 的能力。

Key Improvements over Sonnet 4.6

Sonnet 5 在推理、编码、知识工作和工具使用方面提供了实质性的改进。早期访问合作伙伴报告称，该模型能够更出色地完成复杂的、多步骤的任务而不会停滞，并且它经常在无需提示的情况下进行自我纠正和输出验证。

Specific real-world applications highlighted by partners include:

• Software Engineering: Handling sustained coding, debugging, and tracing failures to root causes in "brownfield" code (legacy codebases).
• Automation: Completing end-to-end workflows, such as updating Salesforce account tiers and sending launch announcements.
• Legal Research: Improving legal research and analysis for plaintiff-law tasks.
• Data Analysis: Reducing time-to-insight by reasoning in tighter steps when exploring live data.
• Insurance Workflows: Executing submission intake and loss runs on existing operational systems.

Performance Benchmarks

In evaluations using BrowseComp (agentic search) and OSWorld-Verified (computer use), Sonnet 5 is a strict improvement over Sonnet 4.6. While Opus 4.8 remains the superior choice for maximum accuracy, Sonnet 5 allows developers to balance cost and performance by adjusting the "effort" level.

Safety and Cybersecurity Guardrails

Sonnet 5 exhibits a lower rate of undesirable behaviors and hallucinations compared to Sonnet 4.6, making it safer for agentic contexts. It is more resistant to prompt injection attacks and better at refusing malicious requests.

Cybersecurity Limitations

Anthropic did not deliberately train Sonnet 5 on cybersecurity tasks. Consequently, it performs substantially worse than Opus 4.8 and Mythos 5 on dangerous cyber skills, such as developing software exploits. In tests involving Firefox 147 vulnerabilities, Sonnet 5 was unable to develop a full working exploit, though it showed a slightly higher partial success rate than Sonnet 4.6 due to general intelligence gains.

Because of this slight increase in capability, Sonnet 5 is launched with real-time cyber safeguards enabled by default to detect and block dangerous usage.

Availability and Pricing

Claude Sonnet 5 is available to all users across Free, Pro, Max, Team, and Enterprise plans. It is also integrated into Claude Code and the Claude Platform.

API Pricing

To account for a tokenizer change that increases token counts by approximately 1.0–1.35×, Anthropic has introduced introductory pricing to keep the transition cost-neutral:

Period	Input Tokens (per million)	Output Tokens (per million)
Through August 31, 2026	$2	$10
After August 31, 2026	$3	$15

Developers can access the model via the API using the identifier claude-sonnet-5.