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 1.05m-token context window. On SWE-bench Verified, Claude Mythos Preview leads by 11.3 pts. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Claude Mythos Preview is safer overall; choose GPT-5.5 when coding workflow support matters.
Decision scorecard
Local evidence first| Signal | Claude Mythos Preview | GPT-5.5 |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | reasoning-heavy apps, multimodal apps, and tool-calling agents |
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 1m | 1.05m |
| Cheapest output | $125/1M tokens | $30/1M tokens |
| Provider routes | 2 tracked | 4 tracked |
| Shared benchmarks | SWE-bench Verified leader | 2 shared |
Decision tradeoffs
- Claude Mythos Preview holds a shared-benchmark lead on SWE-bench Verified, ahead by 11.3 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 route or tier on this page.
Claude Mythos Preview
$51,250
Cheapest tracked route/tier: Anthropic
GPT-5.5
$11,500
Cheapest tracked route/tier: OpenAI API 0-272K input tokens
Estimated monthly gap: $39,750. Batch, cache, alternate speed tiers, 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 | 2026-05-01 | 2026-04-23 |
| Context window | 1m | 1.05m |
| Parameters | — | — |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Weights | Not released | Not released |
| Code | Unknown | Unknown |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | 2025-12 | 2025-12 |
Pricing and availability
| Pricing attribute | Claude Mythos Preview | GPT-5.5 |
|---|---|---|
| Input price | $25/1M tokens |
|
| Output price | $125/1M 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 |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
| Benchmark | Claude Mythos Preview | GPT-5.5 |
|---|---|---|
| SWE-bench Verified | 93.9 | 82.6 |
| 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 82.6, with Claude Mythos Preview ahead by 11.3 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 11.3 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 on the cheapest tracked provider, while GPT-5.5 lists tiered pricing: 0-272K input tokens is $5/1M input and $30/1M output; 272K+ input tokens is $8/1M input and $36/1M output. A 70/30 input-output blend puts GPT-5.5 lower by about $42.50 per million blended tokens. For tiered rows, this cheapest-track view can understate interactive or fast-lane spend, so compare the tier you will actually use. Availability is 2 providers versus 4, 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 cheapest-tier 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 1.05m 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?
Claude Mythos Preview lists $25/1M input and $125/1M output tokens on the cheapest tracked provider. GPT-5.5 lists tiered pricing: 0-272K input tokens is $5/1M input and $30/1M output; 272K+ input tokens is $8/1M input and $36/1M output. Compare the tier you will actually use; cheap async pricing can overstate savings for interactive workflows. 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 and Microsoft Foundry. GPT-5.5 is available on OpenAI API, OpenRouter, Vercel AI Gateway, and AWS Bedrock. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-06-29. Data sourced from public model cards and provider documentation.