Claude Mythos Preview vs GPT-5.5
Claude Mythos Preview (2026) and GPT-5.5 (2026) are frontier-tier reasoning models from Anthropic and OpenAI. Claude Mythos Preview ships a 1M-token context window, while GPT-5.5 ships a 1.1M-token context window. On SWE-bench Verified, Claude Mythos Preview leads by 5.2 pts. On pricing, GPT-5.5 costs $5/1M input tokens versus $25/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit.
GPT-5.5 is ~400% cheaper at $5/1M; pay for Claude Mythos Preview only for coding workflow support.
Decision scorecard
Local evidence first| Signal | Claude Mythos Preview | GPT-5.5 |
|---|---|---|
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 1M | 1.1M |
| Cheapest output | $125/1M tokens | $30/1M tokens |
| Provider routes | 1 tracked | 2 tracked |
| Shared benchmarks | SWE-bench Verified leader | 2 rows |
Decision tradeoffs
- Claude Mythos Preview leads the largest shared benchmark signal on SWE-bench Verified by 5.2 points.
- Local decision data tags Claude Mythos Preview for Coding, RAG, and Agents.
- GPT-5.5 has the larger context window for long prompts, retrieval packs, or transcript analysis.
- GPT-5.5 has the lower cheapest tracked output price at $30/1M tokens.
- GPT-5.5 has broader tracked provider coverage for fallback and procurement flexibility.
- Local decision data tags GPT-5.5 for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output prices on this page.
Claude Mythos Preview
$51,250
Cheapest tracked route: Anthropic
GPT-5.5
$11,500
Cheapest tracked route: OpenAI API
Estimated monthly gap: $39,750. Batch, cache, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for Claude Mythos Preview and GPT-5.5; plan for SDK, billing, or endpoint changes.
- GPT-5.5 is $95/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- No overlapping tracked provider route is sourced for GPT-5.5 and Claude Mythos Preview; plan for SDK, billing, or endpoint changes.
- Claude Mythos Preview is $95/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-04-07 | 2026-04-23 |
| Context window | 1M | 1.1M |
| Parameters | — | — |
| Architecture | decoder only | decoder only |
| License | Proprietary | Proprietary |
| Knowledge cutoff | 2025-12 | 2025-12 |
Pricing and availability
| Pricing attribute | Claude Mythos Preview | GPT-5.5 |
|---|---|---|
| Input price | $25/1M tokens | $5/1M tokens |
| Output price | $125/1M tokens | $30/1M tokens |
| Providers |
Capabilities
| Capability | Claude Mythos Preview | GPT-5.5 |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | Yes |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | Yes |
Benchmarks
| Benchmark | Claude Mythos Preview | GPT-5.5 |
|---|---|---|
| SWE-bench Verified | 93.9 | 88.7 |
| Google-Proof Q&A | 94.6 | 93.6 |
Deep dive
On shared benchmark coverage, SWE-bench Verified has Claude Mythos Preview at 93.9 and GPT-5.5 at 88.7, with Claude Mythos Preview ahead by 5.2 points; Google-Proof Q&A has Claude Mythos Preview at 94.6 and GPT-5.5 at 93.6, with Claude Mythos Preview ahead by 1 points. The largest visible gap is 5.2 points on SWE-bench Verified, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
The capability footprint is close: both models cover vision, multimodal input, reasoning mode, function calling, and tool use. That makes context budget, benchmark fit, and provider maturity more important than a simple checklist. If your application depends on one integration detail, verify it against the provider route you plan to use, not just the base model listing.
For cost, Claude Mythos Preview lists $25/1M input and $125/1M output tokens, while GPT-5.5 lists $5/1M input and $30/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts GPT-5.5 lower by about $42.50 per million blended tokens. Availability is 1 providers versus 2, so concentration risk also matters.
Choose Claude Mythos Preview when coding workflow support are central to the workload. Choose GPT-5.5 when coding workflow support, larger context windows, and lower input-token cost are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship.
FAQ
Which has a larger context window, Claude Mythos Preview or GPT-5.5?
GPT-5.5 supports 1.1M tokens, while Claude Mythos Preview supports 1M tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Claude Mythos Preview or GPT-5.5?
GPT-5.5 is cheaper on tracked token pricing. Claude Mythos Preview costs $25/1M input and $125/1M output tokens. GPT-5.5 costs $5/1M input and $30/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Claude Mythos Preview or GPT-5.5 open source?
Claude Mythos Preview is listed under Proprietary. GPT-5.5 is listed under Proprietary. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, Claude Mythos Preview or GPT-5.5?
Both Claude Mythos Preview and GPT-5.5 expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, Claude Mythos Preview or GPT-5.5?
Both Claude Mythos Preview and GPT-5.5 expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Where can I run Claude Mythos Preview and GPT-5.5?
Claude Mythos Preview is available on Anthropic. GPT-5.5 is available on OpenAI API and OpenRouter. Provider coverage can affect latency, region availability, compliance posture, and fallback options. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Continue comparing
Last reviewed: 2026-05-11. Data sourced from public model cards and provider documentation.