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- Sep 29, 202590% CONFIDENCEfrom the source
Claude Sonnet 4.5 Released
- Anthropic called it "the best coding model in the world. It's the strongest model for building complex agents. It's the best model at using computers"[1][4]
- "Available everywhere today" as claude-sonnet-4-5 on the Claude API and in the Claude apps; Mike Krieger said it would be the default and recommended it for "basically every use case"[1][5]
- It shipped with Claude Code checkpoints and a native VS Code extension, a context editing feature and memory tool on the API, code execution and file creation in the Claude apps, and the Claude Agent SDK, the infrastructure behind Claude Code[1][4]
- "This is the most aligned frontier model we've ever released", with lower rates of sycophancy and deception, released under AI Safety Level 3 (ASL-3) protections[1][3][4]
- It arrived less than two months after Claude Opus 4.1, with Anthropic valued at $183 billion[4][5]
Notable features
- $3 per million input tokens and $15 per million output tokens, as for Sonnet 4; 200K-token context window, 64K max output and a January 2025 reliable knowledge cutoff[1][2]
- 77.2% on SWE-bench Verified, averaged over 10 trials with no test-time compute, and 82.0% with parallel test-time compute[1]
- It leads OSWorld computer use at 61.4%, where Sonnet 4 had led at 42.2% four months earlier[1]
- Anthropic observed it holding focus for more than 30 hours on complex multi-step tasks; CNBC notes Opus 4 managed seven[1][5]
- Experts in finance, law, medicine and STEM found its domain knowledge and reasoning well ahead of older models, including Opus 4.1[1]
Benchmarks[1]
| Benchmark | Claude Sonnet 4.5 | Claude Opus 4.1 | Claude Sonnet 4 | GPT-5 | Gemini 2.5 Pro |
|---|---|---|---|---|---|
| Agentic coding (SWE-bench Verified) | 77.2% / 82.0% with parallel test-time compute | 74.5% / 79.4% with parallel test-time compute | 72.7% / 80.2% with parallel test-time compute | 72.8% (GPT-5) / 74.5% (GPT-5-Codex) | 67.2% |
| Agentic terminal coding (Terminal-Bench) | 50.0% | 46.5% | 36.4% | 43.8% | 25.3% |
| Agentic tool use (τ2-bench), retail | 86.2% | 86.8% | 83.8% | 81.1% | — |
| Agentic tool use (τ2-bench), airline | 70.0% | 63.0% | 63.0% | 62.6% | — |
| Agentic tool use (τ2-bench), telecom | 98.0% | 71.5% | 49.6% | 96.7% | — |
| Computer use (OSWorld) | 61.4% | 44.4% | 42.2% | — | — |
| High school math competition (AIME 2025) | 100% (python) / 87.0% (no tools) | 78.0% | 70.5% | 99.6% (python) / 94.6% (no tools) | 88.0% |
| Graduate-level reasoning (GPQA Diamond) | 83.4% | 81.0% | 76.1% | 85.7% | 86.4% |
| Multilingual Q&A (MMMLU) | 89.1% | 89.5% | 86.5% | 89.4% | — |
| Visual reasoning (MMMU validation) | 77.8% | 77.1% | 74.4% | 84.2% | 82.0% |
| Financial analysis (Finance Agent) | 55.3% | 50.9% | 44.5% | 46.9% | 29.4% |
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- [1]90%anthropic.com/news/claude-sonnet-4-5anthropic.com· Posted Sep 28, 2026· Starts Sep 29, 2025 ✓· 29% of score
The post is dated "Sep 29, 2025" and says "Claude[2] Sonnet 4.5 is available everywhere today"; the docs model page lists "Released September 29, 2025" and TechCrunch[4] reports the launch "On Monday".
- [2]90%Claude Sonnet 4.5 - Claude Platform Docsplatform.claude.com· Added Sep 28, 2026· 29% of score
Anthropic's[1][3] model page: claude-sonnet-4-5-20250929, 200K context window, 64K max output, $3/$15 per million tokens, extended thinking, text and images in, a January 2025 reliable knowledge cutoff, "Released September 29, 2025".
- [3]90%System Card: Claude Sonnet 4.5anthropic.com· Added Sep 28, 2026· 29% of score
Anthropic's[1] system card for Claude[2] Sonnet 4.5, "a new hybrid reasoning large language model" (September 2025), with the alignment and safety evaluations behind its ASL-3 release.
- [4]85%Anthropic launches Claude Sonnet 4.5, its best AI model for codingtechcrunch.com· Published Sep 29, 2025· Starts Sep 29, 2025· 7% of score
TechCrunch, 2025-09-29: "On Monday, Anthropic[1][3] launched a new frontier model called Claude[2] Sonnet 4.5" at Sonnet 4's $3/$15; researcher David Hershey saw it code autonomously for up to 30 hours; it arrives less than two months after Claude Opus 4.1.
- [5]85%Anthropic launches Claude Sonnet 4.5, its latest AI model that's 'more of a colleague'cnbc.com· Published Sep 29, 2025· Starts Sep 29, 2025· 7% of score
CNBC, 2025-09-29: available to all users from the $183 billion startup; Mike Krieger says it will be the default and recommends it for "basically every use case"; it runs autonomously for 30 hours against Opus 4's seven.
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