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Claude Mythos

Claude Mythos Preview is Anthropic's most advanced AI model to date.
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Claude Mythos

Anthropic's most ambitious model yet, blending mythic-scale reasoning with practical precision.

What is Claude Mythos?

Where most model names communicate tier (Haiku, Sonnet, Opus) or generation, Mythos points toward a different category altogether — a model intended to explore capability ceilings, not simply refine existing ones.

A general-purpose model with an unexpected edge

Claude Mythos was designed to push the limits of software engineering — to build an AI that could work through vast, complex codebases with minimal guidance. What Anthropic discovered was that those same coding and reasoning improvements produced, as a side effect, cybersecurity capabilities that exceed anything previously seen in a commercial AI model.

Sitting above the Opus tier

Claude Mythos is not an incremental upgrade to Opus. It represents a new capability tier entirely — one that Anthropic has described as "substantially beyond" every model they have previously trained. The gap on agentic coding benchmarks alone is large enough to constitute a qualitative jump, not a marginal improvement.

What Mythos Preview is built to do

Extended multi-step reasoning

Mythos is designed to pursue long chains of logic without losing thread, particularly useful in legal analysis, mathematical proofs, and complex code architectures where earlier models could drift or contradict themselves partway through.

Deep scientific and technical synthesis

The model is tailored for trusted organizations working at research frontiers, where the task isn't just finding answers, but critically evaluating conflicting evidence across disciplines and producing defensible conclusions.

Long-context sustained coherence

Maintaining accuracy and relevance across very large input windows has been a known weakness in prior models. Mythos Preview targets this gap specifically, keeping reasoning grounded even when working with lengthy documents, codebases, or research bodies.

High-stakes judgment and ethical nuance

Given its restricted access and Anthropic's safety-first framing, Mythos is also expected to demonstrate particularly strong alignment properties, handling sensitive domains with the kind of calibrated judgment that has historically been difficult to achieve at high capability levels.

Advanced agentic task completion

Frontier models increasingly serve as autonomous agents rather than simple query-response tools. Mythos is built with that architecture in mind, performing multi-turn, multi-tool tasks over extended time horizons without constant human guidance.

Benchmark performance

Claude Mythos Preview sets new records across coding, mathematics, reasoning, and cybersecurity. The gaps below show Mythos versus Claude Opus 4.6, its immediate predecessor.

Cybersecurity capabilities

Where Mythos most visibly separates from the field and why Anthropic chose to restrict its release rather than ship it openly.

Security Capability Result Details
Zero-days discovered autonomously
Internal deployment findings
10,000+ High or critical severity vulnerabilities reportedly discovered across major operating systems and browsers during Mythos's first month of internal deployment beginning February 24, 2026.
CTF success rate (expert-level)
UK AISI evaluation
73% Successfully completed advanced multistep infiltration and cybersecurity challenge tasks at rates reportedly beyond previous AI system performance levels.
Notable findings during testing
Real-world vulnerability discoveries
OpenBSD TCP SACK RCE FreeBSD NFS RCE Firefox JS exploits
Mythos Preview reportedly identified a 27-year-old OpenBSD TCP SACK remote code execution vulnerability, a 17-year-old FreeBSD NFS RCE vulnerability tracked as CVE-2026-4747, and executed 181 Firefox JavaScript engine exploits during testing.
OSS-Fuzz corpus results
Open-source fuzzing performance
7,000 entry points 595 tier 1–2 crashes 10 control-flow hijacks
Across approximately 7,000 OSS-Fuzz entry points, Mythos reportedly generated hundreds of critical crash findings and achieved ten complete control-flow hijacks against fully patched targets using a single execution attempt per target.

Mythos Preview within the Claude model family

Understanding Mythos Preview requires understanding how Anthropic structures its model lineup. Claude comes in three public tiers — Haiku (fast, lightweight), Sonnet (balanced), and Opus (powerful, more deliberate). Mythos Preview sits outside this structure entirely.

Model Tier / Purpose
Claude Haiku 4.5 Speed-optimized for everyday tasks and high-throughput workloads.
Claude Sonnet 4.6 Balanced performance, capability, and speed for most use cases.
Claude Opus 4.6 / 4.7 / 4.8 High-capability models designed for advanced reasoning and general-purpose work.
Claude Mythos Preview Frontier research model focused on maximum capability and cutting-edge performance.

What is Claude Mythos?

Where most model names communicate tier (Haiku, Sonnet, Opus) or generation, Mythos points toward a different category altogether — a model intended to explore capability ceilings, not simply refine existing ones.

A general-purpose model with an unexpected edge

Claude Mythos was designed to push the limits of software engineering — to build an AI that could work through vast, complex codebases with minimal guidance. What Anthropic discovered was that those same coding and reasoning improvements produced, as a side effect, cybersecurity capabilities that exceed anything previously seen in a commercial AI model.

Sitting above the Opus tier

Claude Mythos is not an incremental upgrade to Opus. It represents a new capability tier entirely — one that Anthropic has described as "substantially beyond" every model they have previously trained. The gap on agentic coding benchmarks alone is large enough to constitute a qualitative jump, not a marginal improvement.

What Mythos Preview is built to do

Extended multi-step reasoning

Mythos is designed to pursue long chains of logic without losing thread, particularly useful in legal analysis, mathematical proofs, and complex code architectures where earlier models could drift or contradict themselves partway through.

Deep scientific and technical synthesis

The model is tailored for trusted organizations working at research frontiers, where the task isn't just finding answers, but critically evaluating conflicting evidence across disciplines and producing defensible conclusions.

Long-context sustained coherence

Maintaining accuracy and relevance across very large input windows has been a known weakness in prior models. Mythos Preview targets this gap specifically, keeping reasoning grounded even when working with lengthy documents, codebases, or research bodies.

High-stakes judgment and ethical nuance

Given its restricted access and Anthropic's safety-first framing, Mythos is also expected to demonstrate particularly strong alignment properties, handling sensitive domains with the kind of calibrated judgment that has historically been difficult to achieve at high capability levels.

Advanced agentic task completion

Frontier models increasingly serve as autonomous agents rather than simple query-response tools. Mythos is built with that architecture in mind, performing multi-turn, multi-tool tasks over extended time horizons without constant human guidance.

Benchmark performance

Claude Mythos Preview sets new records across coding, mathematics, reasoning, and cybersecurity. The gaps below show Mythos versus Claude Opus 4.6, its immediate predecessor.

Cybersecurity capabilities

Where Mythos most visibly separates from the field and why Anthropic chose to restrict its release rather than ship it openly.

Security Capability Result Details
Zero-days discovered autonomously
Internal deployment findings
10,000+ High or critical severity vulnerabilities reportedly discovered across major operating systems and browsers during Mythos's first month of internal deployment beginning February 24, 2026.
CTF success rate (expert-level)
UK AISI evaluation
73% Successfully completed advanced multistep infiltration and cybersecurity challenge tasks at rates reportedly beyond previous AI system performance levels.
Notable findings during testing
Real-world vulnerability discoveries
OpenBSD TCP SACK RCE FreeBSD NFS RCE Firefox JS exploits
Mythos Preview reportedly identified a 27-year-old OpenBSD TCP SACK remote code execution vulnerability, a 17-year-old FreeBSD NFS RCE vulnerability tracked as CVE-2026-4747, and executed 181 Firefox JavaScript engine exploits during testing.
OSS-Fuzz corpus results
Open-source fuzzing performance
7,000 entry points 595 tier 1–2 crashes 10 control-flow hijacks
Across approximately 7,000 OSS-Fuzz entry points, Mythos reportedly generated hundreds of critical crash findings and achieved ten complete control-flow hijacks against fully patched targets using a single execution attempt per target.

Mythos Preview within the Claude model family

Understanding Mythos Preview requires understanding how Anthropic structures its model lineup. Claude comes in three public tiers — Haiku (fast, lightweight), Sonnet (balanced), and Opus (powerful, more deliberate). Mythos Preview sits outside this structure entirely.

Model Tier / Purpose
Claude Haiku 4.5 Speed-optimized for everyday tasks and high-throughput workloads.
Claude Sonnet 4.6 Balanced performance, capability, and speed for most use cases.
Claude Opus 4.6 / 4.7 / 4.8 High-capability models designed for advanced reasoning and general-purpose work.
Claude Mythos Preview Frontier research model focused on maximum capability and cutting-edge performance.

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