Claude Sonnet 4.5
Anthropic's coding and agentic workflow specialist with extended thinking, computer use, and a 200K context window. Renas AI's chat default — and Anthropic's claim for the best coding model in the world.
Model Specs
- Released
- Sep 2025
- Context window
- 200K tokens
- Max output
- 64K tokens
- Capabilities
- extended-thinkingcomputer-useagentic-workflowsfunction-calling
- Modalities
- textvision
About this model
Claude Sonnet 4.5 is Anthropic's mid-tier flagship, released on September 29, 2025. Anthropic positions it as the best coding model in the world, with state-of-the-art results on SWE-bench Verified (77.2% with the standard 200K thinking budget, 82.0% on high-compute runs). It pairs a 200,000-token context window with extended thinking, native computer use (controlling browsers, file systems, apps), and the ability to maintain focus on a single complex task for 30+ hours of agentic operation.
On Renas AI, Claude Sonnet 4.5 is the chat default — when you open AI Chat without changing the model, you're talking to Sonnet 4.5. It's also the recommended choice in the AI Editor, the Blog Wizard, and any workflow that involves software engineering, complex agentic reasoning, or long-form writing where Anthropic's polished output voice is preferred. Pricing is 0.07 credits per word — the same tier as GPT-5.2 and Grok 3, three times cheaper than Claude Opus 4.1.
The model excels at three things in particular: software engineering (the SWE-bench leadership is real and reproducible), agentic computer-use tasks (browser automation, multi-step research, tool orchestration), and long-form writing where you want Anthropic's characteristic clarity and structure. For tasks where you specifically need OpenAI's structured output reliability or Grok's real-time data, switch models — for everything else, Sonnet 4.5 is the safe default.
Key Strengths
State-of-the-art coding (SWE-bench 77.2%)
Anthropic's announcement and independent benchmarks both place Sonnet 4.5 at the top of SWE-bench Verified — real GitHub issues solved end-to-end. With 200K thinking budget, 77.2%; with high-compute, 82.0%. This is the model to use for software engineering.
Native computer use
Sonnet 4.5 can control browsers, file systems, and applications directly — clicking buttons, filling forms, reading screens, navigating menus. Useful for automation workflows that go beyond pure text generation.
30+ hour task focus
Anthropic reports the model can stay on task for over 30 hours of continuous agentic operation. For long-running research, multi-step coding projects, or complex automation chains, this means fewer derails compared to shorter-attention models.
Extended thinking with adaptive budget
Sonnet 4.5 thinks longer when problems are harder and shorter when they're easy. You don't have to manually pick between fast and reasoning modes — the model adapts.
Polished writing voice
Anthropic models are widely preferred for long-form writing — clearer structure, more natural transitions, less repetition. For blog posts, reports, and editorial content where voice matters, Sonnet 4.5 often beats GPT-5 family on raw quality.
Renas AI chat default
When you open AI Chat on Renas, Sonnet 4.5 is the model you're talking to by default. The platform-wide default reflects its broad applicability — solid on writing, strong on code, capable on reasoning.
Benchmarks
How it compares
Sonnet 4.5 sits in the flagship-adjacent tier — same price as GPT-5.2 and Grok 3, three times cheaper than Claude Opus 4.1. Each makes a different trade-off on strengths.
| vs. Model | Verdict | Outcome |
|---|---|---|
| GPT-5.2 | GPT-5.2 has stronger benchmark scores on pure reasoning (GPQA Diamond 93.2, AIME 100) and a larger 400K context window. Sonnet 4.5 leads on SWE-bench Verified (77.2% vs GPT-5.2 not publicly reporting this benchmark) and is widely preferred for long-form writing voice. Pick GPT-5.2 for reasoning-heavy or vision-heavy tasks; Sonnet 4.5 for coding and writing. | Depends |
| Claude Opus 4.1 | Opus 4.1 is Anthropic's premium tier — 5x more expensive ($15/$75 per M tokens vs $3/$15) and the predecessor flagship. Sonnet 4.5 actually outperforms Opus 4.1 on SWE-bench (77.2% vs 74.5%). Stick with Sonnet 4.5 unless you specifically need Opus's writing character or have an existing pipeline validated against it. | Wins most cases |
| Claude Haiku 4.5 | Haiku 4.5 is the budget Anthropic option (0.025 vs 0.07 credits per word) with similar coding quality (SWE-bench 73.3% vs 77.2%) at 2x the speed. For high-volume work and rapid iteration, Haiku is the better choice. For complex agentic tasks or critical code, Sonnet's stronger benchmark gap is worth the cost. | Wins most cases |
Pros
- Top SWE-bench Verified score (77.2%) — best for coding tasks
- Native computer use — control browsers, file systems, apps directly
- 30+ hour task focus for long-running agentic workflows
- 200K context with extended thinking and adaptive budget
- Polished writing voice — preferred for long-form editorial content
- Renas AI chat default — broadest applicability across surfaces
Things to consider
- Smaller context window than GPT-5 family (200K vs 400K)
- More expensive than Haiku 4.5 (3x) for tasks that don't need flagship-tier capability
- Less benchmark coverage on pure-reasoning evals (GPQA, AIME) than OpenAI models
- Computer-use feature requires careful permissions setup for production use
Best use cases
Software engineering and code review
Bug fixes that span multiple files, architecture proposals, complex refactors, code review. Sonnet 4.5's SWE-bench leadership translates directly to real-world coding tasks.
Long-form writing and editorial
Blog posts, whitepapers, reports, technical articles. Anthropic's writing voice is polished and structured — often the right pick when the output will be published as-is.
Agentic automation workflows
Multi-step research tasks, browser automation, customer support agents that orchestrate multiple tools. The 30+ hour focus capability matters here.
Document analysis and synthesis
Read long contracts, financial filings, research papers — synthesize findings, extract structured data, answer questions across the full document. The 200K context handles most realistic inputs.
Strategic and analytical reasoning
Decision frameworks, scenario planning, pros/cons analyses. Extended thinking with adaptive budget gives careful answers without manual mode switching.
Multimodal work with images
Vision input for UI reviews, scientific figure interpretation, document OCR + analysis. Same multimodal capabilities as the GPT-5 family.
How to use it on Renas AI
- 1
Step 1
Open any Renas AI surface
Sonnet 4.5 is available in AI Chat (the default model), AI Editor, Blog Wizard, AI Text Generator, and the WordPress plugin. The model behaves identically across surfaces — pick the one that matches your workflow.
- 2
Step 2
Confirm the model picker
On Renas AI, Sonnet 4.5 is selected by default in chat. In other tools, double-check the model picker — choose Sonnet 4.5 for coding, agentic work, and long-form writing. Switch to Opus 4.1 only when you need the absolute top-tier output and the cost is justified.
- 3
Step 3
Provide context and constraints
Paste full files, describe the task, list constraints (style, output format, success criteria). The 200K context fits entire codebases, long documents, and multi-document inputs in one message.
- 4
Step 4
Iterate, export, or hand off
Read the response, follow up in the same conversation, export to Markdown / Word / WordPress. For repeated workflows, save the prompt as a Persona — Sonnet 4.5 retains its character well across long sessions.
Pricing
Pricing on Renas AI
Pay-as-you-go credits, no API keys, no rate limits.
~142,857 words on a 10,000-credit Spark plan
Frequently asked questions
Other Anthropic models
Other text models on Renas AI
Use the Renas AI default model
Run Claude Sonnet 4.5 with your Renas AI subscription credits — no API key, no setup, no per-seat fees.
Try Claude Sonnet 4.5