Anthropic Claude Mythos 5 (1M) vs OpenAI GPT-5.5 Pro (1M)
Side-by-side comparison of pricing, context window, capabilities, and a real-cost sample workload.
Option A
Anthropic Claude Mythos 5 (1M)
by Anthropic
Context: 1M
Input: $12.00 / 1M
Output: $60.00 / 1M
Released: 2026-06
Option B
OpenAI GPT-5.5 Pro (1M)
by OpenAI
Context: 1M
Input: $30.00 / 1M
Output: $180.00 / 1M
Released: 2026-04
Detailed Comparison
| Dimension | Anthropic Claude Mythos 5 (1M) | OpenAI GPT-5.5 Pro (1M) |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Context window TieTie | 1M | 1M |
| Input price ($/1M) Winner | $12.00 | $30.00 |
| Output price ($/1M) Winner | $60.00 | $180.00 |
| Sample workload cost Winner 1M input + 500K output tokens
|
$42.00 | $120.00 |
| Released Winner | 2026-06 | 2026-04 |
| Tokenizer | claude-4 | o200k_base |
The verdict
On the dimensions we measured, Anthropic Claude Mythos 5 (1M) wins more often - particularly on cost-effectiveness for a typical 1M+0.5M workload.
Anthropic Claude Mythos 5 (1M) - Key features
Anthropic's most powerful frontier model - the Mythos-class system with state-of-the-art agentic and cybersecurity capability. Distributed under strict access controls; Fable 5 is its safeguarded public sibling.
- Mythos-class frontier intelligence
- State-of-the-art long-horizon agents
- Adaptive thinking + effort control
- 1M token context window
- Leading code & security reasoning
OpenAI GPT-5.5 Pro (1M) - Key features
A higher-accuracy GPT-5.5 variant for the most demanding tasks, available via the API at premium pricing.
- Maximum accuracy GPT-5.5 tier
- ~1.05M token context window
- 128K max output tokens
- Best for hard reasoning
- API-only
How to choose
- Pick the cheaper model if your workload is mostly straightforward classification, extraction, or summarization.
- Pick the bigger context if you process long documents, large codebases, or multi-document research.
- Pick the more recent release if you need state-of-the-art reasoning quality and don't mind paying a bit more.
- Use both via a routing layer - send simple tasks to the cheaper one and complex tasks to the smarter one. This is the highest-ROI optimization in production AI.
Estimate the real cost of either model for your prompts using our Token Calculator.