Claude Mythos 5.1 vs Claude Opus 5.5
Benchmarks, API Token Pricing, Context Window & Speed Comparison
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Claude Mythos 5.1 by Anthropic and Claude Opus 5.5 by Anthropic represent two of the frontier AI models analyzed in our comprehensive 2026 AI benchmark and LLM comparison. In this head-to-head evaluation, we examine API token pricing, context window specifications, inference speed (tokens per second), and empirical reasoning performance. From a pure economic perspective, Claude Opus 5.5 holds a notable pricing advantage for token ingestion. On output generation, Claude Opus 5.5 is more economical per million generated tokens. In data-heavy architectures requiring extensive repository or document analysis, both models provide an identical memory horizon with 1,000K tokens. In latency-sensitive production environments, Claude Opus 5.5 leads in tokens-per-second throughput, making it ideal for real-time conversational agents and high-concurrency workflows. Below is the complete empirical head-to-head breakdown across cost, speed, context, and capability matrices.
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Claude Mythos 5.1
Restricted FrontierAnthropic's restricted frontier capability tier (Project Glasswing), shared exclusively with vetted national cybersecurity and life-science research organizations.
$15.00 / 1M
$75.00 / 1M
1M tokens
84.2%
Claude Opus 5.5
Frontier Intelligence TitanAnthropic's most intelligent model for complex reasoning, research, and strategic analysis.
$4.00 / 1M
$20.00 / 1M
1M tokens
84.6%
Key Differences at a Glance
- Claude Opus 5.5 is 3.8x cheaper for API usage (input + output tokens combined).
- Claude Opus 5.5 is faster at 78 tok/s vs 60 tok/s.
- Claude Opus 5.5 leads on SWE-bench coding (84.6% vs 84.2%).
| Feature | Claude Mythos 5.1 | Claude Opus 5.5 |
|---|---|---|
Intelligence Index Composite reasoning & knowledge score (0-100) | 88 | 94 |
Provider | Anthropic | Anthropic |
Input Price Cost per million input tokens | $15.00 / 1M | $4.00 / 1M |
Output Price Cost per million output tokens | $75.00 / 1M | $20.00 / 1M |
Blended Price Weighted 7:2:1 cache:input:output per 1M | $11.55 / 1M | $3.08 / 1M |
Context Window Maximum input + output tokens | 1M tokens~1,500 A4 pages of text | 1M tokens~1,500 A4 pages of text |
Max Output Tokens Per single request | 128K | 128K |
Throughput Speed Tokens generated per second | 60 tok/s | 78 tok/s |
SWE-bench Verified Real-world software engineering | 84.2% | 84.6% |
GPQA Diamond Graduate-level reasoning | 82% | 82.3% |
Cached Input Price Prompt caching discount per 1M tokens | $1.50 / 1M | $0.40 / 1M |
Who Wins Where?
At-a-glance decision frameworkEmpirical Head-to-Head Benchmark Scores
Official evaluation metrics verified by independent third-party research labs.
Industry benchmark evaluating real-world GitHub issue resolution and multi-file debugging.
Challenging questions created by domain experts to test complex PhD-level reasoning.
Hardened reasoning and academic knowledge benchmark with reduced lucky-guess probability.
Crowdsourced human preference evaluation based on blind, head-to-head model battles.
Extremely difficult, closed-ended questions spanning the frontier of human expert knowledge.
Autonomous multi-step tasks executed inside a real command-line terminal environment.
Research-grade coding problems drawn from real scientific and numerical workloads.
Contamination-free competitive programming problems collected continuously over time.
American Invitational Mathematics Examination — multi-step Olympiad-level reasoning.
Accuracy when reasoning over very large inputs that fill the model context window.
Tokens emitted per second during active generation streaming.
Latency & Response Time
Time to first token (TTFT) and estimated end-to-end response time for a typical 500-token response.
Real-Time Interactive Token Cost Simulator
Adjust sliders to calculate projected monthly cloud API spending with prompt caching discounts.
Claude Mythos 5.1 · Strengths & Key Advantages
- State-of-the-art capability under Project Glasswing for autonomous biological and cyber defense
- Superhuman code synthesis and multi-repository vulnerability validation
- Extreme rigor in formal logical reasoning
Considerations & Trade-offs
- Gated access: strictly unavailable to the general public or unvetted commercial entities
- Stringent compliance oversight and continuous human-in-the-loop audit logs required
Claude Opus 5.5 · Strengths & Key Advantages
- Unmatched autonomous multi-step agentic coding and refactoring
- Flawless multi-document reasoning over 1M token context with no long-prompt surcharge
- Highest composite Intelligence Index score measured (94/100), leading SWE-bench Verified at 84.6%
- Precise tool execution with robust error-recovery loops
Considerations & Trade-offs
- Premium output pricing ($20.00/M) plus heavy reasoning-token usage (~68K output tokens per complex task) keeps long agentic runs expensive
- Long thinking times at maximum effort can push a single hard agentic task toward ~$3.85+
Token Use & Task Economics
Estimated cost and token consumption to complete one representative agentic task.
| Metric | Claude Mythos 5.1 | Claude Opus 5.5 |
|---|---|---|
Cost per Task Estimated USD to finish one task | $16.46 | $3.85 |
Output Tokens / Task Tokens generated per task | 72K | 68K |
Reasoning Tokens / Task Thinking tokens burned per task | 37K | 42K |
Technical Specifications
Architecture, release timeline, capabilities, and modalities.
| Feature | Claude Mythos 5.1 | Claude Opus 5.5 |
|---|---|---|
| Official API Model ID (SDK) | claude-mythos-5-1-20260901 | claude-opus-5-5-20260901 |
| API Protocol | Anthropic Messages API + AWS Bedrock + Vertex AI | Anthropic Messages API + AWS Bedrock + Vertex AI |
| Release Date | 2026-09 | 2026-09 |
| Knowledge Cutoff | June 2026 | June 2026 |
| Architecture | Restricted Frontier Autonomous Cognitive System | Extended Autonomous Hybrid Reasoning Transformer |
| Parameters | Confidential | Confidential |
| Enterprise Rate Limits (RPM / TPM) | 4,000 – 10,000 RPM (Tier 4 + Priority Tier) · 4,000,000 – 10,000,000 TPM | 4,000 – 10,000 RPM (Tier 4 + Priority Tier) · 4,000,000 – 10,000,000 TPM |
| Long-Context Tier (>128K/200K) | Standard rate up to 200K tokens; 2x input/output tier above 200K tokens | Standard rate up to 200K tokens; 2x input/output tier above 200K tokens |
| Prompt Cache Policy & TTL | $1.5/1M cached read (90% off); 5-min default & 1-hour extended TTL | $0.4/1M cached read (90% off); 5-min default & 1-hour extended TTL |
| Computer Use / GUI Agent | Supported (Screen coordinate grounding, browser & desktop GUI action loops) | Supported (Screen coordinate grounding, browser & desktop GUI action loops) |
| MCP & Parallel Tool Calling | Native MCP Client/Server ready · Parallel function calling · 100% Strict JSON Schema | Native MCP Client/Server ready · Parallel function calling · 100% Strict JSON Schema |
| Web Search Grounding & Sandbox | Native Web Search Citations + Code Execution Tool + MCP Connectors | Native Web Search Citations + Code Execution Tool + MCP Connectors |
| Official Fine-Tuning Support | Custom Model Tuning via Amazon Bedrock & Prompt Distillation | Custom Model Tuning via Amazon Bedrock & Prompt Distillation |
| Multimodal Token Billing | Text BPE (~4 chars/token) · Vision (~258–765 tokens per image tile) | Text BPE (~4 chars/token) · Vision (~258–765 tokens per image tile) |
| Quantization & Min GPU VRAM | Cloud-Hosted Proprietary (FP8 / BF16 Tensor Core Cluster) · Zero Local VRAM Required (100% Serverless Cloud API) | Cloud-Hosted Proprietary (FP8 / BF16 Tensor Core Cluster) · Zero Local VRAM Required (100% Serverless Cloud API) |
| Safety & Frontier Classification | Anthropic RSP ASL-2 / ASL-3 Constitutional Safety Evaluated | Anthropic RSP ASL-2 / ASL-3 Constitutional Safety Evaluated |
| Enterprise Compliance (ZDR/HIPAA/SOC2) | SOC2 Type II · GDPR · Zero Data Retention (ZDR) & HIPAA BAA Available on Enterprise Tier | SOC2 Type II · GDPR · Zero Data Retention (ZDR) & HIPAA BAA Available on Enterprise Tier |
| Input Modalities | text, vision | text, vision |
| Output Modalities | text | text |
Claude Mythos 5.1 vs Claude Opus 5.5: Quick Answers
Which is more intelligent, Claude Mythos 5.1 or Claude Opus 5.5?
Claude Opus 5.5 is more intelligent. It scores 94 compared with 88 on the composite Intelligence Index.
Which model is faster?
Claude Opus 5.5 is faster, generating 78 tokens per second compared with 60 tokens per second.
Which model is cheaper to run?
Claude Opus 5.5 is cheaper at $3.08 per 1M tokens blended, compared with $11.55 (7:2:1 cache:input:output ratio).
Which model has lower latency?
Claude Opus 5.5 has lower latency, with a time to first token of 1.40s compared with 1.60s.
Verdict
Verdict & Model Selection Recommendation: Choose Claude Mythos 5.1 if your priority is National defense cybersecurity hardening, advanced biological countermeasures, and frontier safety research. Its performance in demanding tasks justifies its operational token cost. Choose Claude Opus 5.5 if your workflow prioritizes Large-scale software development agents, enterprise codebases, and mission-critical scientific synthesis. For large-scale batch processing or customer-facing conversational interfaces, its balance of speed and economics delivers superior ROI.
Frequently asked questions
How does Claude Mythos 5.1 compare to Claude Opus 5.5 in API token pricing and cost per token?+
Claude Mythos 5.1 costs $15.00 per 1M input tokens and $75.00 per 1M output tokens, whereas Claude Opus 5.5 costs $4.00 input and $20.00 output. Overall, Claude Opus 5.5 is the more cost-effective model for high-volume API pipelines. Both models support prompt caching discounts of up to 90% for repeated prompt prefixes.
Which model has a larger context window: Claude Mythos 5.1 or Claude Opus 5.5?+
Both Claude Mythos 5.1 and Claude Opus 5.5 offer an identical context window of 1,000K tokens (~750k words). Both architectures provide equal capacity for large document ingestion, multi-file codebases, and extended multi-turn conversation histories.
Which AI model is better for software engineering and coding: Claude Mythos 5.1 or Claude Opus 5.5?+
Claude Mythos 5.1 scores 84.2% on SWE-bench Verified while Claude Opus 5.5 scores 84.6%. For autonomous software engineering and multi-file debugging, Claude Opus 5.5 holds the verified benchmark lead.
What is the difference in reasoning capability and extended thinking between Claude Mythos 5.1 and Claude Opus 5.5?+
Claude Mythos 5.1 features native chain-of-thought extended thinking mode with configurable reasoning effort. In contrast, Claude Opus 5.5 provides chain-of-thought reasoning depth for complex math and science.
How does inference speed (tokens per second) compare between Claude Mythos 5.1 and Claude Opus 5.5?+
Claude Mythos 5.1 generates approximately 60 tokens per second, while Claude Opus 5.5 delivers 78 tokens per second. In latency-sensitive production environments, Claude Opus 5.5 provides faster time-to-first-token (TTFT) and higher streaming response velocity.
Can you implement a tiered LLM routing setup combining Claude Mythos 5.1 and Claude Opus 5.5 to optimize costs?+
Yes! High-efficiency architectures route high-frequency routine classification and conversational tasks to Claude Opus 5.5 to save operational costs, and dynamically escalate complex architectural queries or reasoning tasks to Claude Mythos 5.1. This tiered routing pattern cuts overall API bills by up to 70%.
Understand key metrics like context window, token pricing, reasoning mode, and SWE-bench scores in our comprehensive AI glossary.
Related reading
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Benchmark scores, token prices, and rate limits evolve rapidly as AI labs release model updates. Always verify current specifications and pricing on the official provider documentation.
Sources: GetInfoUs Independent AI Benchmarks & Official API Specs