Claude Mythos 5 vs GPT-5.5
Too close to call on our weighted score (GPT-5.5 36, Claude Mythos 5 36). The right pick depends on what you value most.
AnthropicClaude Mythos 5
36/100- ECI—
- Price$10.00 / $50.00
- Context1M
OpenAIGPT-5.5
36/100- ECI159.2
- Price$5.00 / $30.00
- Context1.05M
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Make it a three-way comparison.
Too close to call
It is close. Our weighted score puts them within a point (GPT-5.5 36/100, Claude Mythos 5 36/100), so choose by what matters most for your work: GPT-5.5 on price and GPT-5.5 for long inputs. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
- CapabilityNot enough dataNo independent benchmark covers every model here yet
- Lowest priceGPT-5.5GPT-5.5 $11.25 · Claude Mythos 5 $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-5.5GPT-5.5 1,050,000 · Claude Mythos 5 1,000,000 tokens
- Widest inputsSame inputsClaude Mythos 5: Text, Images, PDFs · GPT-5.5: Text, Images, PDFs
- Self-hostingNo open weightsBoth are available only through APIs
| Measure | Weight | Claude Mythos 5 | GPT-5.5 |
|---|---|---|---|
| Price | 50% | 0 | 0 |
| Inputs & features | 30% | 80 | 80 |
| Context window | 20% | 60 | 61 |
| Overall | 100% | 36/100 | 36/100 |
Left out because at least one model lacks the data: capability. The remaining weights were rescaled.
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Mythos 5Anthropic | GPT-5.5OpenAI |
|---|---|---|
| Capability | ||
| Capabilities Index (ECI) | — | 159.2 |
| ECI rank | — | #10 of 148 |
| GPQA DiamondGraduate-level science questions | — | 94.0% |
| FrontierMath Tiers 1–3Research-level mathematics | — | 85.3% |
| OTIS Mock AIME 2024–2025Competition mathematics | — | 100% |
| SWE-bench VerifiedFixing real GitHub issues | — | 80.6% |
| SimpleQA VerifiedShort factual questions | — | 63.0% |
| Price per million tokens | ||
| Input | $10.00 | $5.00 (best) |
| Output | $50.00 | $30.00 (best) |
| Cached input | — | $0.50 |
| Blended (3:1) | $20.00 | $11.25 (best) |
| Long-context rate | Same rate | Over 272K: $10.00 / $45.00 |
| Price source | Median of 2 providers | Official OpenAI API |
| Limits | ||
| Context window | 1,000,000 tokens | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | 128,000 tokens |
| Inputs and features | ||
| Text | Yes | Yes |
| Images | Yes | Yes |
| PDFs | Yes | Yes |
| Audio | No | No |
| Video | No | No |
| Reasoning | Yes | Yeslow · medium · high · xhigh |
| Tool calling | Yes | Yes |
| Structured output | Yes | Yes |
| Availability | ||
| Weights | Proprietary | Proprietary |
| API model ID | — | gpt-5.5 |
| API providers | 2 | 42 (best) |
| Released | Jun 9, 2026 | Apr 23, 2026 |
| Knowledge cutoff | Jan 31, 2026 | Dec 1, 2025 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Claude Mythos 5$200.00
- GPT-5.5$110.00
Which should you choose?
Which is better: Claude Mythos 5 or GPT-5.5?
It is close. Our weighted score puts them within a point (GPT-5.5 36/100, Claude Mythos 5 36/100), so choose by what matters most for your work: GPT-5.5 on price and GPT-5.5 for long inputs. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
Which is cheaper, Claude Mythos 5 or GPT-5.5?
GPT-5.5 is cheaper at $5.00 input / $30.00 output per million tokens (official OpenAI API price). Claude Mythos 5 costs $10.00 input / $50.00 output per million tokens (median across 2 API providers). At a typical mix of three input tokens to one output token, that is $11.25 per million tokens for GPT-5.5 versus $20.00 for Claude Mythos 5 (1.8× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers both models yet. Claude Mythos 5 has not been scored yet and GPT-5.5 has an ECI of 159.2.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Mythos 5 yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. Both support tool calling for agent workflows.
Which has the bigger context window?
GPT-5.5 has the largest context window at 1,050,000 tokens, against 1,000,000 for Claude Mythos 5. Maximum output per response: Claude Mythos 5 up to 128,000, GPT-5.5 up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Mythos 5 accepts text, images and PDFs; GPT-5.5 accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
No. Claude Mythos 5 and GPT-5.5 are proprietary and only available through APIs and apps.
Which is newer?
Claude Mythos 5 is the newest, released Jun 9, 2026. GPT-5.5 came out Apr 23, 2026. Knowledge cutoff: Claude Mythos 5 Jan 31, 2026, GPT-5.5 Dec 1, 2025.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
