Best AI Reasoning Models for Vellum
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Compare the Top AI Reasoning Models that integrate with Vellum as of September 2026
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This a list of AI Reasoning Models that integrate with Vellum. Use the filters on the left to add additional filters for products that have integrations with Vellum. View the products that work with Vellum in the table below.
What are AI Reasoning Models for Vellum?
AI reasoning models are artificial intelligence models designed to perform complex problem-solving, logical reasoning, planning, and multi-step decision-making beyond traditional language generation. These models use advanced inference techniques to break down difficult tasks, evaluate alternatives, apply logic, and generate more accurate responses for domains such as mathematics, programming, scientific research, business analysis, and autonomous AI agents. AI reasoning models often support extended context windows, tool use, code execution, structured outputs, and agentic workflows to solve complex real-world problems. Many are available through APIs, cloud platforms, and AI development frameworks, enabling developers to build intelligent applications and autonomous systems. By combining language understanding with advanced reasoning capabilities, AI reasoning models help organizations improve decision-making, automate complex workflows, and power next-generation AI applications. Compare and read user reviews of the best AI Reasoning Models for Vellum currently available using the table below. This list is updated regularly.
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1
Claude Mythos 5.1
Anthropic
Claude Mythos 5.1 is Anthropic’s newest Mythos-class model, designed for advanced cybersecurity, biology, scientific research, coding, and long-running knowledge work. It is the same underlying model as Claude Fable 5.1 but uses different safeguards: Fable 5.1 is generally available, while Mythos 5.1 is restricted to trusted access programs with safeguards specifically designed for cybersecurity and life sciences research. The model sets a new performance frontier for agentic coding and demonstrates the strongest cyber capabilities of any Anthropic model released to date. In scientific research, Mythos 5.1 can work with specialized tools and complex workflows across molecular design, computational biology, and other technical domains. In Anthropic’s experiments, it designed high-affinity protein binders across multiple targets and achieved its strongest measured hit rate to date. It also optimized seven open-source protein and genomics deep learning models. -
2
Claude Opus 5.5
Anthropic
Claude Opus 5.5 is Anthropic’s advanced AI model for agentic coding, complex knowledge work, computer use, research, and long-running professional tasks. It is designed to handle large codebases, multi-step workflows, financial analysis, document creation, software audits, and other demanding workloads with improved efficiency over Claude Opus 5. Anthropic reports that Opus 5.5 uses fewer tokens per task, produces output more than 30% faster, and costs less to run than its predecessor. The model also improves communication quality by putting important information first, reducing unnecessary jargon, and following writing instructions more consistently. Safety enhancements include stronger prompt-injection resistance, action screening, sandboxing support, code review, behavioral alignment testing, and safeguards for high-risk cybersecurity & biology. Claude Opus 5.5 is available through Claude, Claude Code, the Claude Platform API, Amazon Web Services, Google Cloud, and Microsoft Azure.Starting Price: $4 per 1M tokens (input) -
3
Claude Opus 5
Anthropic
Claude Opus 5 is Anthropic’s advanced everyday AI model built for coding, knowledge work, problem-solving, visual outputs, and production AI workflows. The model delivers stronger performance than Opus 4.8 at the same base price and is positioned as a cost-effective alternative close to Claude Fable 5 frontier intelligence. Claude Opus 5 supports configurable effort settings so users can optimize for intelligence, speed, or token efficiency. It performs especially well on software engineering, automation, computer use, scientific research, and knowledge work evaluations. The model is available on Claude Max, Claude Pro, Claude API, Claude Code, and other Claude platforms, with Fast mode available at a higher price. Built for developers, researchers, enterprises, and everyday Claude users, Claude Opus 5 helps teams complete complex tasks with stronger verification, careful iteration, and practical cost efficiency.Starting Price: $5 per 1M tokens (input) -
4
Claude Fable 5
Anthropic
Claude Fable 5 is an advanced AI model from Anthropic designed to assist with software engineering, research, knowledge work, vision tasks, and complex reasoning. Built on the Mythos-class architecture, it delivers significantly improved performance across coding, analysis, and long-context workflows. The model can handle extended autonomous tasks while maintaining focus and consistency over large amounts of information. Claude Fable 5 integrates advanced reasoning, multimodal understanding, and memory capabilities to support professional and enterprise use cases. Anthropic has implemented specialized safeguards that automatically route certain high-risk cybersecurity, biology, chemistry, and model distillation requests to a different model. Claude Fable 5 helps organizations and professionals accelerate complex work while maintaining strong safety and governance controls.Starting Price: $10 per 1 million (input) -
5
Claude Opus 4.8
Anthropic
Claude Opus 4.8 is a powerful AI model from Anthropic designed to deliver stronger coding, reasoning, agentic workflows, and advanced collaboration capabilities for developers, enterprises, and AI-powered productivity tasks. The model builds on Claude Opus 4.7 with improvements across coding benchmarks, practical knowledge work, alignment, and reliability while maintaining the same pricing structure. Claude Opus 4.8 introduces enhanced honesty and reasoning behavior, making it less likely to generate unsupported claims or overlook flaws during complex tasks such as software development and agent execution. The release also includes new features such as effort control settings, fast mode for lower-cost high-speed processing, and dynamic workflows in Claude Code that allow the system to coordinate hundreds of parallel subagents for large-scale tasks.Starting Price: $5 per 1M (input)
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