Claude Sonnet 4.5
Released
Claude Sonnet 4.5 is an AI model released by Anthropic on Monday, Sep 29 2025, 55 days after Claude Opus 4.1. Benchmark results (shown below) cover BullshitBench v2, SWE-Bench Verified, Next.js Evals, ARC-AGI-2, GPQA Diamond, OSWorld-Verified, and 1 more.
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API pricing
- InputWhat you pay for everything you send the model — your question, plus any documents or earlier conversation you include with it.
- $3.00
- Cached inputA reduced rate for text you send over and over. If every request starts with the same instructions or the same document, the provider keeps a copy ready and charges less to read it again.
- $0.30
- 5 min cache writeA one-off charge for storing text so later requests can reuse it at the cheaper cached rate. This option keeps it for five minutes.
- $3.75
- 1 hr cache writeA one-off charge for storing text so later requests can reuse it at the cheaper cached rate. This option keeps it for an hour, so it costs more than the five-minute one.
- $6.00
- OutputWhat you pay for the text the model writes back. It is normally the dearer half: producing an answer costs more than reading one.
- $15.00
Available from
| Amazon Bedrock | — | $3.00 | $15.00 | 1M |
|---|---|---|---|---|
| Azure | global | $3.00 | $15.00 | 200K |
| global | $3.00 | $15.00 | 1M | |
| Amazon Bedrock | eu-west-1 | $3.30 | $16.50 | 1M |
| us-east5 | $3.30 | $16.50 | 1M |
Benchmarks
Coding
Agentic & tool use
Reasoning & science
Multimodal
Robustness
Source: BenchLM, retrieved 31 August 2026. Every other score here is the figure the lab published at launch.
About
Claude Sonnet 4.5, released September 29, 2025, was introduced by Anthropic as the best coding model in the world at the time. It reached 77.2% on SWE-Bench Verified and 83.4% on GPQA Diamond, and it was built for autonomy: Anthropic reported it could work productively on complex, multi-step tasks for many hours without losing the thread — the capability that underpinned the Claude Agent SDK, released the same day.
Beyond raw scores, Sonnet 4.5 marked the point where the mid-tier Sonnet line overtook the previous flagship Opus 4.1 on software-engineering benchmarks while remaining far cheaper, a pattern that repeated across the industry as labs pushed agentic training into smaller models. It was succeeded at the top of the coding leaderboards by Claude Opus 4.5 in November 2025.
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Frequently asked questions
Claude Sonnet 4.5 was released by Anthropic on Monday, Sep 29 2025.