Side by side
Standard-tier prices in effect today. The better value in each row is highlighted.
| Fact | Claude Mythos 5.1 | GPT-5.5 |
|---|---|---|
| Price per 1M input tokens | $10 | $5 (better) |
| Price per 1M output tokens | $50 | $30 (better) |
| Cost of 10M input and 2M output tokens | $200 | $110 (better) |
| Arena Text | Not measured | 1482 Elo (#13 of 39) |
| GPQA Diamond | Not measured | 90.7% (#21 of 37) |
| FrontierMath Tiers 1-3 (v2) | Not measured | 85.3% (#11 of 37) |
| SimpleQA Verified | Not measured | 63% (#13 of 34) |
| LiveBench Overall | Not measured | 79.91 points (#1 of 5) |
| Provider | Anthropic | OpenAI |
| Release date | September 1, 2026 | April 23, 2026 |
| Access | API only | API only |
| Context window | Not reported | 1,050,000 tokens |
| Max output | Not reported | 128,000 tokens |
| Input | text, image | text, image |
| Output | text | text |
Scores:Arena · 2026-10-12Epoch AI · 2026-10-12LiveBench · 2026-06-25
When to choose each
Claude Mythos 5.1
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
GPT-5.5
Best for
- High-capability API evaluations with long context
Watch out for
- Prompts above the provider long-context threshold use higher token rates; validate the selected reasoning effort against production cost
Claude Mythos 5.1 vs GPT-5.5 FAQ
Which is cheaper, Claude Mythos 5.1 or GPT-5.5?
GPT-5.5 is 50% cheaper per 1M input tokens than Claude Mythos 5.1, $5 vs $10. For 10M input and 2M output tokens, Claude Mythos 5.1 costs $200 and GPT-5.5 $110 at standard rates.
Related comparisons
Production evaluation
Choosing between Claude Mythos 5.1 and GPT-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