Kimi K3.1 Pro vs. Claude Sonnet 5.5

Kimi K3.1 Pro is a multimodal large language model developed by Moonshot AI to support advanced reasoning, autonomous AI agents, software development, 3D creation, and complex knowledge work. The model is based on a mixture-of-experts architecture containing approximately 2.8 trillion total parameters and 104 billion active parameters. Its one-million-token context window enables the processing of extensive documents, source code repositories, technical materials, and long-running task histories. Kimi K3.1 Pro builds on the Kimi K3 foundation with additional reinforcement learning and post-training optimization across programming, analytical reasoning, and agentic tasks. Its software engineering capabilities include code generation, debugging, terminal operations, automated testing, application development, and multistep problem-solving across existing repositories. The model can develop interactive websites, animated interfaces, browser-based 3D environments, and game projects using tools and frameworks such as Three.js, Unity, Unreal Engine, and Godot. Its multimodal reasoning capabilities allow it to interpret images, sketches, and visual references when generating technical designs or structured outputs. Three-dimensional modeling features include CAD script generation, parametric geometry creation, asset modification, and integration with tools such as Blender. Financial reasoning capabilities support complex spreadsheet models, financial statement analysis, investment research, cross-document verification, and evidence-based reporting. Kimi K3.1 Pro also supports tool-assisted workflows in which AI agents plan tasks, execute actions, evaluate results, and refine outputs across multiple steps. The model is available through Kimi's web and mobile applications, Kimi Work, Kimi Code, and the Kimi API, with a Highspeed variant providing faster inference and an open-weight release planned for November 4, 2026.

Claude Sonnet 5.5 is Anthropic’s faster, lower-cost Claude 5.5 model for well-scoped professional work, software development, agentic workflows, and content creation. Anthropic positions it below Claude Opus 5.5 for the most complex open-ended work, but says it can perform comparably on some benchmarks when run at higher effort settings. The model delivers a particularly large improvement in coding, including a 70.6% result on Terminal-Bench 4.0, 46.2% on FrontierCode at Max effort, and 55.5% on CursorBench 4.0. It also scores 1844 on GDPval-AA, 1811 on AA-Briefcase, 64.5% on Humanity’s Last Exam with tools, and 80.1% on OSWorld 2.1 partial. Anthropic reports that Sonnet 5.5 is better at long-horizon work, image understanding, collaboration, and codebase comprehension than Sonnet 5. The company also highlights design-oriented improvements, including the ability to produce polished documents, spreadsheets, slides, and user interfaces with less editing. Sonnet 5.5 generates output more than 30% faster than its predecessor and is Anthropic’s fastest Sonnet model to date. Although its listed token prices are unchanged from Sonnet 5, Anthropic says greater token efficiency can reduce per-task cost by up to 30%. Pricing is $2 per million input tokens, $10 per million output tokens, $2.50 per million cache-write tokens, and $0.20 per million cache-read tokens. The model includes cyber safeguards, biology safeguards, reasoning-extraction protections, and preserved-thinking controls, with some higher-risk cyber requests falling back to Sonnet 5. Claude Sonnet 5.5 is available with zero data retention across Claude products, the Claude Platform, AWS, Google Cloud, and Microsoft Azure under the model name claude-sonnet-5-5.