What is Claude Sonnet 4.5?
Claude Sonnet 4.5 is Anthropic's balanced performance model, released on September 29, 2025. Anthropic positioned it as "the best coding model in the world" at launch. It scores 77.2% on SWE-bench Verified — the leading real-world coding benchmark — and supports a 200,000 token context window with an experimental 1 million token option in beta. At $3 per million input tokens and $15 per million output tokens, it delivers frontier capability at mid-range pricing.
What Makes Claude Sonnet 4.5 Different?
The headline feature is context awareness — the ability to maintain coherent understanding across extremely long conversations and documents. Sonnet 4.5 can sustain autonomous operation for over 30 hours on complex tasks, making it genuinely viable for long-horizon agentic applications. It also introduces extended thinking, computer use (clicking, typing, navigating interfaces), and strong instruction following that earlier Sonnet models lacked.
Compared to its predecessor Sonnet 4, the improvement is substantial: better coding accuracy, fewer refusals on benign edge cases, and tighter adherence to complex instructions. Many developers who used Opus 4.1 switched to Sonnet 4.5 because it matched Opus performance at 80% lower cost.
Claude Sonnet 4.5 Pricing
Input tokens cost $3 per million, output tokens cost $15 per million. Prompt caching writes cost $3.75 per million and reads just $0.30 per million — a 90% discount on cached content. Batch processing gives a 50% output discount for asynchronous workloads. The model is available via Anthropic's API, Amazon Bedrock, and Google Cloud Vertex AI.
Claude Sonnet 4.5 vs GPT-5 vs Gemini
Against GPT-5, Claude Sonnet 4.5 costs more ($3/$15 vs $1.25/$10) but is preferred by many developers for its more natural writing style, stronger instruction following, and lower hallucination rate on ambiguous queries. Against Gemini 3 Flash, Sonnet 4.5 costs more but delivers considerably stronger reasoning. For most production coding and analysis workloads, Sonnet 4.5 represents the optimal balance in Anthropic's lineup as of early 2026 — though Sonnet 4.6 (February 2026) now improves on it further.
Who Should Use Claude Sonnet 4.5?
Claude Sonnet 4.5 is ideal for software engineering agents, document analysis, customer support automation, and any task requiring strong instruction following and reliable outputs. It's the default choice for teams building with Claude who need more than Haiku but don't want Opus pricing. Note that Claude Sonnet 4.6, released February 17, 2026, is now the recommended version at the same price point with improved coding scores.
Frequently Asked Questions
What is the context window for Claude Sonnet 4.5?
The standard context window is 200,000 tokens. An experimental 1 million token option is available in beta via Anthropic's API. Max output is 64,000 tokens per response.
Does Claude Sonnet 4.5 support computer use?
Yes. Claude Sonnet 4.5 supports computer use — the ability to interact with desktop interfaces, click buttons, type text, and navigate applications autonomously.