text model comparison
Claude Mythos 5.1 vs Claude Opus 5.5
Claude Mythos 5.1 and Claude Opus 5.5 are both current text models, from Anthropic. Claude Opus 5.5 is 60% cheaper per 1M input tokens than Claude Mythos 5.1, $4 vs $10.
- Lower price per 1M input tokens
- Claude Opus 5.5$4 against $10
- Newer release
- Claude Opus 5.5Sep 22, 2026 against Sep 1, 2026
Data verified November 3, 2026 · Dataset 2026-11-03
Side by side
Claude Mythos 5.1 and Claude Opus 5.5, line by line
Prices in effect today, compared at the same tier wherever both list one. The better value in each row is highlighted.
| Fact | Claude Mythos 5.1 | Claude Opus 5.5 |
|---|---|---|
| Price | ||
| Price per 1M input tokens | $10 | $4 (better) |
| Price per 1M output tokens | $50 | $20 (better) |
| Independent benchmarks | ||
| Arena Text | Not measured | 1509 Elo (#2 of 51) |
| Arena WebDev | Not measured | 1810 Elo (#1 of 45) |
| FrontierMath Tiers 1-3 (v2) | Not measured | 91.2% (#3 of 42) |
| GPQA Diamond | Not measured | 90.6% (#25 of 41) |
| SimpleQA Verified | Not measured | 72.2% (#5 of 38) |
| Specs | ||
| Provider | Anthropic | Anthropic |
| Release date | September 1, 2026 | September 22, 2026 |
| Access | API only | API only |
| Context window | Not reported | 1,000,000 tokens |
| Max output | Not reported | 128,000 tokens |
| Input | text, image | text, image |
| Output | text | text |
No independent benchmark has scored both models yet. Each rank counts the current models scored on that benchmark.
Charts
Against every current text model
Where Claude Mythos 5.1 and Claude Opus 5.5 land among the current models of their task, on every independent benchmark, on price and on context.
Where each stands
Only Claude Opus 5.5 has a current Arena Text score: #2 of 51. Each bar is the share of current models it beats.
Independent benchmarks
Arena Text
Claude Mythos 5.1: Not scored
Claude Opus 5.5:#2of 51
1,509 Elo · ahead of 98%
Arena WebDev
Claude Mythos 5.1: Not scored
Claude Opus 5.5:#1of 45
1,810 Elo · ahead of 100%
FrontierMath Tiers 1-3 (v2)
Claude Mythos 5.1: Not scored
Claude Opus 5.5:#3of 42
91.2% · ahead of 95%
GPQA Diamond
Claude Mythos 5.1: Not scored
Claude Opus 5.5:#25of 41
90.6% · ahead of 40%
SimpleQA Verified
Claude Mythos 5.1: Not scored
Claude Opus 5.5:#5of 38
72.2% · ahead of 89%
Price and context
Price per 1M input tokens
Claude Mythos 5.1:#49of 52
$10 · cheaper than 0%
Claude Opus 5.5:#43of 52
$4 · cheaper than 14%
Price per 1M output tokens
Claude Mythos 5.1:#49of 52
$50 · cheaper than 0%
Claude Opus 5.5:#43of 52
$20 · cheaper than 14%
Context window
Claude Mythos 5.1: Not listed
Claude Opus 5.5:#26of 64
1M tokens · longer than 22%
Quality against price
Claude Opus 5.5 scores 1,509 at $8 (blended price per 1M tokens). The line joins the current models no other beats on both price and Arena Text score; hover any point to name it.
Quality against price: the data
| Model | Provider | Blended price per 1M tokens | Arena Text (Elo) |
|---|---|---|---|
| Gemini 4 Argon | $4 | 1,520 | |
| Claude Opus 5.5 | Anthropic | $8 | 1,509 |
| Muse Wonder | Meta | $8 | 1,507 |
| Claude Fable 5 | Anthropic | $20 | 1,504 |
| Claude Fable 5.1 | Anthropic | $20 | 1,504 |
| Gemini 3.8 Flash | $1.50 | 1,496 | |
| Muse Spark 1.3 | Meta | $2 | 1,495 |
| Claude Opus 5 | Anthropic | $10 | 1,492 |
| Kimi K3 | Moonshot Kimi | $6 | 1,488 |
| GPT-5.6 Sol | OpenAI | $8 | 1,485 |
| Gemini 3.6 Flash | $3 | 1,483 | |
| GPT-5.5 | OpenAI | $11 | 1,482 |
| Claude Opus 4.8 | Anthropic | $10 | 1,482 |
| Qwen3.8-Max | Alibaba Qwen | $3 | 1,482 |
| GPT-6.1 Sol | OpenAI | $4 | 1,481 |
| GLM-5.3 | Z.ai | $2.15 | 1,481 |
| MiMo-V2.6-Pro | Xiaomi MiMo | $0.54 | 1,480 |
| Claude Sonnet 5.5 | Anthropic | $4 | 1,477 |
| GLM-5.3-Flash | Z.ai | $0.24 | 1,477 |
| GPT-6 Astra | OpenAI | $20 | 1,476 |
| DeepSeek-V4.1-Flash | DeepSeek | $0.52 | 1,476 |
| GPT-5.4 | OpenAI | $5.63 | 1,475 |
| Gemini 3 Flash Preview | $1.13 | 1,473 | |
| Grok 4.20 | xAI | $1.56 | 1,472 |
| GPT-5.6 Terra | OpenAI | $4.50 | 1,467 |
| Grok 4.5 | xAI | $3 | 1,465 |
| DeepSeek-V4-Pro | DeepSeek | $1.98 | 1,465 |
| Claude Sonnet 5 | Anthropic | $4 | 1,462 |
| GPT-6 Sol | OpenAI | $4 | 1,458 |
| Gemini 3.5 Flash-Lite | $0.85 | 1,456 | |
| Grok 4.6 | xAI | $3 | 1,455 |
| GPT-5.6 Luna | OpenAI | $0.45 | 1,453 |
| MiMo-V2.6-Flash | Xiaomi MiMo | $0.18 | 1,448 |
| Step 5 Preview | StepFun | $1.43 | 1,448 |
| Grok 4.3 | xAI | $1.56 | 1,442 |
| GPT-6 Luna | OpenAI | $0.20 | 1,441 |
| Grok 4.7 | xAI | $3 | 1,441 |
| Mistral Large 4 | Mistral AI | $1.05 | 1,432 |
| Claude Haiku 5.5 | Anthropic | $0.20 | 1,425 |
| GPT-4.1 | OpenAI | $3.50 | 1,415 |
| Solar Pro 4 | Upstage | $0.52 | 1,388 |
| GPT-4.1 mini | OpenAI | $0.70 | 1,383 |
| GPT-4.1 nano | OpenAI | $0.18 | 1,322 |
Cost
What each costs
Example workloads at each provider's listed rates, then every other rate either one lists. The cheaper figure in each row is highlighted.
The same work, priced
For 10M input and 2M output tokens, Claude Mythos 5.1 costs 2.5 times as much as Claude Opus 5.5, at each provider's listed rates.
10M input and 2M output tokens
Claude Mythos 5.1 costs 2.5× as much
- Claude Mythos 5.1
- $200
- Claude Opus 5.5
- $80
The same, with 9M of the input tokens cached
Claude Mythos 5.1 costs 2.5× as much
- Claude Mythos 5.1
- $112.25
- Claude Opus 5.5
- $45.80
| Workload or rate | Claude Mythos 5.1 | Claude Opus 5.5 |
|---|---|---|
| Example workloads | ||
| 10M input and 2M output tokens | $200 | $80 (better) |
| The same, with 9M of the input tokens cached | $112.25 | $45.80 (better) |
| The same, through the batch API | Not listed | $40 |
| Other listed rates | ||
| 1M input tokens, cached | $0.25 | $0.20 (better) |
| 1M input tokens, 5-minute cache write | Not listed | $5 |
| 1M input tokens, 1-hour cache write | Not listed | $8 |
| 1M input tokens, batch | Not listed | $2 |
| 1M output tokens, batch | Not listed | $10 |
Your own bill will differ. These figures use list prices and example workloads. The AI Model Cost Audit reviews your real usage, shortlists models that score as well for each task for less, and estimates the savings.
Launch price $100, regular price $150
Verdict
When to choose each
Claude Mythos 5.1
Where it leads
No measured lead over Claude Opus 5.5 in this data.
Best for
- Organisations already admitted to Anthropic’s limited-availability programme that need frontier capability at Fable 5.1 rates
Watch out for
- Limited availability: access is restricted to organisations vetted through Anthropic’s Glasswing programme, so it cannot be assumed available for a general evaluation
- Anthropic’s public model comparison table does not list a context window or maximum output for Mythos 5.1, so both are recorded as unknown here rather than inferred from Fable 5.1
Claude Opus 5.5
Where it leads
- Lower input and output prices, $4 and $20 vs $10 and $50 per 1M tokens
- Cheaper cached input, $0.20 vs $0.25 per 1M tokens
- Batch pricing, $2 input and $10 output per 1M tokens
Best for
- Long-running agentic coding and knowledge work as the general-purpose default
- Cache-heavy agent loops where the 0.05x read multiplier compounds
Watch out for
- The API effort default is medium here, not high as on Claude Fable 5.1 and Claude Sonnet 5.5, so a like-for-like comparison has to set effort explicitly
- The 4.7-generation tokenizer produces roughly 30% more tokens for the same text than Claude Sonnet 4.6 and earlier, so per-token rates do not compare directly across generations
From benchmark to production
Building on Claude Mythos 5.1 or Claude Opus 5.5?
Public scores rarely hold on your own data. We test both models on your real tasks, then build the agent or pipeline around the one that wins.
AI Model Cost AuditLaunch price $100, regular price $150What the audit includes
FAQ
Claude Mythos 5.1 vs Claude Opus 5.5 FAQ
Which is cheaper, Claude Mythos 5.1 or Claude Opus 5.5?
Claude Opus 5.5 is 60% cheaper per 1M input tokens than Claude Mythos 5.1, $4 vs $10. For 10M input and 2M output tokens, Claude Mythos 5.1 costs $200 and Claude Opus 5.5 $80 at standard rates.
Which is cheaper with prompt caching, Claude Mythos 5.1 or Claude Opus 5.5?
Claude Mythos 5.1 charges $0.25 per 1M cached input tokens, 98% below its standard input rate, and Claude Opus 5.5 $0.20, 95% below. With 9M of 10M input tokens cached and 2M output tokens, Claude Mythos 5.1 costs $112.25 and Claude Opus 5.5 $45.80.
Further reading
More on Claude Mythos 5.1 and Claude Opus 5.5
Articles on Claude Mythos 5.1 and Claude Opus 5.5
- GDPval-AA Chart Fact-Check: Opus 5.5 vs GPT-6 Astra on CostSeptember 24, 2026
- GPT-6 Sol vs Claude Opus 5.5, Plus Luna: Best Value per TaskSeptember 24, 2026
- Claude Opus 5.5 Benchmarks: What the Chart Shows and HidesSeptember 23, 2026
- Claude Opus 5.5: Tops the Independent Index at a Lower PriceSeptember 23, 2026
Related comparisons
- Claude Mythos 5.1 vs GPT-6 Astra
- Claude Haiku 5.5 vs Claude Opus 5.5
- Claude Fable 5.1 vs Claude Mythos 5.1
- Claude Opus 5.5 vs Mistral Large 4
- Claude Fable 5 vs Claude Mythos 5.1
- Claude Opus 5.5 vs Gemini 4 Argon
- Claude Mythos 5.1 vs GPT-5.5
- Claude Opus 5.5 vs GPT-6.1 Sol
- Claude Opus 5.5 vs Claude Sonnet 5.5
- Claude Fable 5 vs Claude Opus 5.5
- Claude Opus 4.8 vs Claude Opus 5.5
- Claude Opus 5.5 vs Gemini 3.1 Pro Preview
Production evaluation
Choosing between Claude Mythos 5.1 and Claude Opus 5.5?
Public benchmarks narrow the shortlist. We run both on your own tasks, data and cost limits, then build the routing and review controls to run the winner in production.
- A head-to-head evaluation on your real workload
- Routing between models by cost and difficulty