High-volume, cost-sensitive work
Choose GPT-5.5
GPT-5.5 costs 44% less on a typical mix of three input tokens for every output token ($11.25 against $20.00 per million tokens).
Claude Mythos 5.1 vs GPT-5.5: price, context and capabilities
Choose Claude Mythos 5.1 for reused prompts and documents (RAG, agents) and the latest release. Choose GPT-5.5 for high-volume, cost-sensitive work and writing and code generation.
In short
- GPT-5.5 is 44% cheaper than Claude Mythos 5.1 at the headline price ($11.25 / 1M tokens vs $20.00 / 1M tokens).
- GPT-5.5 reads more per request: 1.05M tokens against 1M.
- Claude Mythos 5.1 is the newer model (September 2026, against Apr 24, 2026).
Which should you choose?
Each answer below comes straight from the published prices, specifications and independent benchmark results.
Writing and code generation
Choose GPT-5.5
GPT-5.5 charges $30.00 per million output tokens, against $50.00 for Claude Mythos 5.1. Output dominates the bill when answers are long.
Reused prompts and documents (RAG, agents)
Choose Claude Mythos 5.1
Claude Mythos 5.1 charges $0.25 per million cached input tokens, against $0.50 for GPT-5.5.
Latest release
Choose Claude Mythos 5.1
Claude Mythos 5.1 is the newer release (September 2026, against Apr 24, 2026 for GPT-5.5).
Monthly cost at three volumes
| Volume | Claude Mythos 5.1 | GPT-5.5 | Difference |
|---|---|---|---|
| Prototype: 1M input, 250K output tokens | $22.50 | $12.50 | GPT-5.5, $10.00 less |
| Production: 20M input, 5M output tokens | $450.00 | $250.00 | GPT-5.5, $200.00 less |
| Scale: 500M input, 100M output tokens | $10,000 | $5,500 | GPT-5.5, $4,500 less |
Standard rates, without caching or batch discounts. Volumes are per month.
Specifications side by side
| Claude Mythos 5.1 | GPT-5.5 | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Category | Language models | Language models |
| Status | Generally available · Limited access | Legacy |
| Headline price | $20.00 / 1M tokens | $11.25 / 1M tokens |
| Input | $10.00 / 1M tokens | $5.00 / 1M tokens |
| Output | $50.00 / 1M tokens | $30.00 / 1M tokens |
| Cached input | $0.25 / 1M tokens | $0.50 / 1M tokens |
| Context window | 1M | 1.05M |
| Max output | 128k | 128k |
| Released | September 2026 | Apr 24, 2026 |
| Knowledge cutoff | No data | December 2025 |
| Licence | Proprietary | Proprietary |
| Capabilities | Vision, Reasoning, Tool calling, Structured output, Prompt caching, Batch API | Vision, Reasoning, Tool calling, Structured output, Prompt caching, Batch API |
| API model id | claude-mythos-5-1 | gpt-5.5 |
Benchmarks side by side
Leader in bold.
| Benchmark | Claude Mythos 5.1 | GPT-5.5 |
|---|---|---|
| Intelligence Index | No data | 38.4 |
| Terminal-Bench Hard | No data | 60.6% |
| SciCode | No data | 55.8% |
| GPQA Diamond | No data | 93.5% |
| Humanity's Last Exam | No data | 45.8% |
| IFBench (instruction following) | No data | 75.9% |
| τ²-Bench (agentic tool use) | No data | 93.9% |
| MMMU-Pro (visual reasoning) | No data | 79.9% |
| Long-context reasoning (AA-LCR) | No data | 84.3% |
Independent evaluations by Artificial Analysis, run the same way for every model, at the reasoning setting shown. Percentages unless marked as an index.
Frequently asked questions
Should I choose Claude Mythos 5.1 or GPT-5.5?
Choose Claude Mythos 5.1 for reused prompts and documents (RAG, agents) and the latest release. Choose GPT-5.5 for high-volume, cost-sensitive work and writing and code generation.
Which is cheaper, Claude Mythos 5.1 or GPT-5.5?
GPT-5.5 is 44% cheaper than Claude Mythos 5.1 at the headline price ($11.25 / 1M tokens vs $20.00 / 1M tokens).
Which has the larger context window, Claude Mythos 5.1 or GPT-5.5?
GPT-5.5 reads more per request: 1.05M tokens against 1M.
What is the difference between Claude Mythos 5.1 and GPT-5.5?
Claude Mythos 5.1 is made by Anthropic and GPT-5.5 by OpenAI. GPT-5.5 is 44% cheaper than Claude Mythos 5.1 at the headline price ($11.25 / 1M tokens vs $20.00 / 1M tokens). GPT-5.5 reads more per request: 1.05M tokens against 1M. Claude Mythos 5.1 is the newer model (September 2026, against Apr 24, 2026).
How much do Claude Mythos 5.1 and GPT-5.5 cost per month?
At 20 million input and 5 million output tokens a month, Claude Mythos 5.1 costs $450.00 and GPT-5.5 costs $250.00, at standard rates.
Which is newer, Claude Mythos 5.1 or GPT-5.5?
Claude Mythos 5.1 was released on September 2026 and GPT-5.5 on Apr 24, 2026.