Fable 5.1 with the safeguards lifted — partner-only, 60.9% Terminal-Bench 4.0.
100
Coding
97
Writing
99
Research
89
Images
16
Value
98
Long Context
Use this when
Vetted frontier cybersecurity and life-sciences research at the absolute capability ceiling
Skip this if
You don't hold vetted trusted access, or your work never trips Fable 5.1's safeguards — the two models are otherwise identical.
Pricing
$10.00/1M in
$50.00/1M out
→0%since Sep 2026
Context
1M tokens
Speed
Deliberate
Released September 1, 2026 alongside Claude Fable 5.1, continuing the Mythos-class line that began with Project Glasswing's April 2026 private preview. Access is limited to vetted US cybersecurity and life-sciences professionals. Same underlying model, pricing, context window, and cache-read discount as Fable 5.1; the only published difference is the safeguard level and the resulting Terminal-Bench 4.0 score (60.9% vs 55.8%).
60.9% on Terminal-Bench 4.0 — above Fable 5.1's 55.8% and the highest figure Anthropic has published
Same 1M-token context, 128K output, and $10/$50 base pricing as Fable 5.1
Inherits the same 75% cache-read reduction to $0.25 per 1M tokens
Safeguards lifted in areas where Fable 5.1 declines legitimate security and bio research work
Weaknesses
Not generally available — restricted to vetted US organisations under Project Glasswing
No advantage for ordinary work; Fable 5.1 is the same model at the same price for everyone else
Same deliberate, high-latency profile and premium pricing as Fable 5.1
Real-world use cases
What people actually use Claude Mythos 5.1 for.
Vulnerability discovery and exploit reasoning under Anthropic's trusted-access controls
Life-sciences research workflows that the generally available safeguards constrain
Autonomous engineering where Fable 5.1's safety tuning blocks a legitimate response
How Claude Mythos 5.1 compares
The nearest models people weigh against it, and what actually separates them.
vs Claude 3.5 Sonnet — Against Claude 3.5 Sonnet (Anthropic), Claude Mythos 5.1 costs about 40% more per token, takes 5x the context and answers slower. Claude 3.5 Sonnet is the one to check first if the price difference matters more than the ceiling.
vs Claude 3.7 Sonnet (thinking) — Against Claude 3.7 Sonnet (thinking) (Anthropic), Claude Mythos 5.1 costs about 70% more per token and takes 5x the context. Claude 3.7 Sonnet (thinking) is the one to check first if the price difference matters more than the ceiling.
vs Claude Fable 5 — Against Claude Fable 5 (Anthropic), Claude Mythos 5.1 lands within a few percent on price. Which one wins depends on whether context depth or latency is your constraint.
Price History
Claude Mythos 5.1 pricing over time
→0% since Sep 2
7 data points · tracked daily since Sep 2, 2026
Ready to try it?
Start using Claude Mythos 5.1
Vetted frontier cybersecurity and life-sciences research at the absolute capability ceiling. Start free — no card required.
Claude 3.5 Sonnet is Anthropic's mid-cycle flagship model, balancing strong reasoning, coding, and instruction-following with a 200K context window. It sits between Haiku and Opus in Anthropic's lineup, offering near-flagship quality at a lower cost than top-tier models.
Verdict
One of the best models for coding and complex instruction-following, but its premium pricing demands premium use cases.
Quality score
81%
Pricing
$6.00/1M in
$30.00/1M out
Speed
Balanced
3/5 speed
Context
200k tokens
Pricing at $6 input / $30 output per million tokens is significantly higher than GPT-4o ($2.50/$10). Best accessed via Anthropic API or Amazon Bedrock. Claude 3.5 Sonnet (October 2024 version) supersedes the June 2024 release with improved performance.
Claude 3.7 Sonnet with extended thinking enabled — Anthropic's hybrid reasoning model that explicitly deliberates before responding, surfacing its chain-of-thought for complex multi-step problems. It sits between standard Sonnet and full reasoning-only models, balancing depth with practical usability.
Verdict
The most transparent reasoning model on the market — ideal when you need to see and trust the thought process, not just the answer.
Quality score
73%
Pricing
$3.00/1M in
$15.00/1M out
Speed
Deliberate
2/5 speed
Context
200k tokens
Thinking tokens (the internal reasoning trace) count toward output token billing, which can significantly increase costs on complex queries. The thinking budget can often be configured via the API. Best used selectively for tasks that genuinely benefit from deliberation rather than as a default model.
ReasoningExtended ThinkingCodingAgenticAnthropic
Best for
Tackling complex coding challenges, mathematical proofs, and multi-step logical problems where visible reasoning and higher accuracy matter more than speed.
Anthropic's new Mythos-class flagship and the most capable coding model anyone can use — 80.3% SWE-Bench Pro, an 11-point jump over Opus 4.8. 1M context, 128K output, native parallel subagents. Released June 9, 2026.
Verdict
New global #1 — 80.3% SWE-Bench Pro, the most capable model generally available.
Quality score
98%
Pricing
$10.00/1M in
$50.00/1M out
Speed
Deliberate
2/5 speed
Context
1M tokens
Launched June 9, 2026 as the public, Mythos-class release. Available on the Claude API, Microsoft Foundry, and Google Vertex AI. Free for all users until June 22, 2026. Same underlying model as Claude Mythos 5, with safeguards that block specific high-risk cyber responses.
Coding leaderSWE-Bench Pro #1Mythos-classParallel subagentsAgenticLong contextPremiumNew
Best for
The hardest coding tasks, autonomous multi-step agents, and frontier-grade reasoning
Claude Mythos 5.1 costs $10 per million input tokens and $50 per million output tokens on the API. A month of 10M input and 2M output tokens runs about $200.00 at list price, before any batch or caching discounts.
What is Claude Mythos 5.1 best for?
Claude Mythos 5.1 is best for vetted frontier cybersecurity and life-sciences research at the absolute capability ceiling. It is a strong fit when that workflow matters more than the tradeoffs around premium pricing and deliberate speed.
When should I avoid Claude Mythos 5.1?
You don't hold vetted trusted access, or your work never trips Fable 5.1's safeguards — the two models are otherwise identical.
What is a cheaper alternative to Claude Mythos 5.1?
Claude 3.7 Sonnet (thinking) (Anthropic) at $3.00/1M/1M input against Claude Mythos 5.1's $10.00/1M/1M — roughly 70% less per token all in. The most transparent reasoning model on the market — ideal when you need to see and trust the thought process, not just the answer. Compare it first if Claude Mythos 5.1's pricing is the thing stopping you.
What is a faster alternative to Claude Mythos 5.1?
Claude 3.5 Sonnet — balanced against Claude Mythos 5.1's deliberate, with 200k tokens of context. Worth the swap when response time is what your users notice rather than the last few points of reasoning depth.
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