Claude Mythos Preview vs GPT-5.5 Instant
Claude Mythos Preview (2026) and GPT-5.5 Instant (2026) are frontier reasoning models from Anthropic and OpenAI. Claude Mythos Preview ships a 1m-token context window, while GPT-5.5 Instant ships a 400k-token context window. On pricing, GPT-5.5 Instant costs $5/1M input tokens versus $25/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
GPT-5.5 Instant 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 Instant |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | multimodal apps and tool-calling agents |
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 1m | 400k |
| Cheapest output | $125/1M tokens | $30/1M tokens |
| Provider routes | 2 tracked | 1 tracked |
| Shared benchmarks | 0 shared | 0 shared |
Decision tradeoffs
- Claude Mythos Preview has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Claude Mythos Preview has broader tracked provider coverage for fallback and route flexibility.
- Claude Mythos Preview uniquely exposes Reasoning in local model data.
- Local decision data tags Claude Mythos Preview for Coding, RAG, and Agents.
- GPT-5.5 Instant has the lower cheapest tracked output price at $30/1M tokens.
- Local decision data tags GPT-5.5 Instant 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 Instant
$11,500
Cheapest tracked route/tier: OpenAI API
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 Instant; plan for SDK, billing, or endpoint changes.
- GPT-5.5 Instant is $95/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Reasoning before moving production traffic.
- No overlapping tracked provider route is sourced for GPT-5.5 Instant 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.
- Claude Mythos Preview adds Reasoning in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-05-01 | 2026-05-05 |
| Context window | 1m | 400k |
| 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 | 2025-08 |
Pricing and availability
| Pricing attribute | Claude Mythos Preview | GPT-5.5 Instant |
|---|---|---|
| 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 Instant |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | No |
| JSON / 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
No shared benchmark scores are currently available for this pair.
Continue comparing
Popular comparisons for Claude Mythos Preview
Popular comparisons for GPT-5.5 Instant
Last reviewed: 2026-07-26. Data sourced from public model cards and provider documentation.