Claude 4.5 Sonnet: Best Coding Model In The World! Powerful + Agentic! (Fully Tested)

Key Concepts

Claude Sonnet 4.5: Anthropic's new language model, positioned as a leading coding model.
Swaybench Verified Test: A benchmark where Sonnet 4.5 outperforms even Opus 4.1.
Agentic Capabilities: The model's ability to perform complex, multi-step tasks autonomously.
Context Window: The amount of text the model can consider at once (200K tokens, 1M beta).
Kilo Code: An autonomous AI agent platform offering free credits to test Sonnet 4.5.
OS World Computer Use Benchmark: A measure of the model's ability to use computer systems.
Imagine with Claude: A research preview for building apps with Sonnet 4.5.

1. Introduction to Claude Sonnet 4.5

Enthropic has launched Claude Sonnet 4.5, claiming it to be the best coding model globally.
It excels in building complex agents, using computers, and demonstrates improved reasoning and math skills.
Sonnet 4.5 surpasses Opus 4.1 on the Swaybench verified test.
It is the most aligned Frontier model released by Enthropic, showing alignment improvements over previous Claude models.

2. Model Specifications and Pricing

Sonnet 4.5 accepts text and image inputs.
It has a 200K context window, with a 1 million context beta available.
The model has a maximum output of 64k tokens.
The training data cutoff is July 2025.
Pricing is consistent with Sonnet 4: $3 per 1 million input tokens and $15 per 1 million output tokens.

3. Performance Benchmarks

On the Swaybench verify test, Sonnet 4.5 maintained focus for over 30 hours on complex multi-step tasks.
It leads on various benchmarks against proprietary models like GPT-4 codecs, GPT-4, and Gemini 2.5 Pro.
The model excels across coding benchmarks and leads on the OS World computer use benchmark with a score of 61.4%, a significant increase from Sonnet 4's 42.2%.
It performs well on Agentic terminal tasks and regular Agentic tasks, outperforming other models.
The model demonstrates strong reasoning and math capabilities.

4. Agentic Use and New Features

The Claude agent SDK is available.
"Imagine with Claude" is a new research preview for building apps using Sonnet 4.5, available to paid Enthropic plan users.

5. Accessing and Testing the Model

6. Testing Scenarios and Results

Browser-Based OS: The model was tasked with building a browser-based OS to test code generation and system design.
- It successfully generated a browser OS with a file manager, terminal, and calculator in a single shot.
- Additional features like a notepad, settings, and a painter were added upon request.
SAS Landing Page: The model was asked to create a SAS landing page with features and animations using Kilo Code.
- The generated code cost approximately $2.
- The landing page included testimonials, a pricing structure, and an FAQ with animations.
- The front-end design was considered decent but not extraordinary.
- The chatbot version required iteration and was not as impressive.
Butterfly in SVG Code: The model was tasked with creating a butterfly in SVG code to test its ability to output proficient SVG code and develop symmetry.
- The generated butterfly had a decent structure and symmetry, but there were minor issues with the wings and unwanted dots.
Minecraft Clone: The model was tasked with creating a Minecraft clone to test its ability to handle large-scale code processes and design core systems.
- The model successfully replicated the base structure of Minecraft, including grass blocks and the ability to break and place blocks.
- The terrain generation was limited, lacking trees and other terrains.
Solar System Implementation: The model delivered an impressive one-shot solar system implementation with realistic orbits and physics.

7. Additional Resources and Call to Action

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8. Conclusion

Claude Sonnet 4.5 shows significant improvements in agent capabilities and front-end development.
Code generation quality may vary in certain areas, potentially due to context window limitations or areas needing further refinement.
The model is impressive, and the speaker is keen to hear viewers' thoughts on its generations.
Potential improvements are expected with the Claude 5 release.