Claude Mythos Preview vs Grok 4.20 Reasoning
Claude Mythos Preview (2026) and Grok 4.20 Reasoning (2026) are frontier-tier reasoning models from Anthropic and xAI. Claude Mythos Preview ships a 1M-token context window, while Grok 4.20 Reasoning ships a not-yet-sourced context window. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing. The goal is to make the tradeoff clear before deeper testing.
Grok 4.20 Reasoning is safer overall; choose Claude Mythos Preview when coding workflow support matters.
Decision scorecard
Local evidence first| Signal | Claude Mythos Preview | Grok 4.20 Reasoning |
|---|---|---|
| Decision fit | Coding, RAG, and Agents | General |
| Context window | 1M | — |
| Cheapest output | $125/1M tokens | - |
| Provider routes | 2 tracked | 0 tracked |
| Shared benchmarks | 0 rows | 0 rows |
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 procurement flexibility.
- Claude Mythos Preview uniquely exposes Vision, Multimodal, and Function calling in local model data.
- Local decision data tags Claude Mythos Preview for Coding, RAG, and Agents.
- Use Grok 4.20 Reasoning when your own prompt tests beat the comparison signals; the local data does not show a decisive standalone advantage yet.
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
Grok 4.20 Reasoning
Unavailable
No complete token price in local provider data
Cost delta unavailable until both models have sourced input and output token prices.
Switch friction
- No overlapping tracked provider route is sourced for Claude Mythos Preview and Grok 4.20 Reasoning; plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Vision, Multimodal, and Function calling before moving production traffic.
- No overlapping tracked provider route is sourced for Grok 4.20 Reasoning and Claude Mythos Preview; plan for SDK, billing, or endpoint changes.
- Claude Mythos Preview adds Vision, Multimodal, and Function calling in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-04-07 | 2026-05-16 |
| Context window | 1M | — |
| Parameters | — | — |
| Architecture | decoder only | - |
| License | Proprietary | Proprietary |
| Knowledge cutoff | 2025-12 | 2024-11 |
Pricing and availability
| Pricing attribute | Claude Mythos Preview | Grok 4.20 Reasoning |
|---|---|---|
| Input price | $25/1M tokens | - |
| Output price | $125/1M tokens | - |
| Providers | - |
Capabilities
| Capability | Claude Mythos Preview | Grok 4.20 Reasoning |
|---|---|---|
| Vision | Yes | No |
| Multimodal | Yes | No |
| Reasoning | Yes | Yes |
| Function calling | Yes | No |
| Tool use | Yes | No |
| Structured outputs | Yes | No |
| Code execution | Yes | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: Claude Mythos Preview, multimodal input: Claude Mythos Preview, function calling: Claude Mythos Preview, tool use: Claude Mythos Preview, structured outputs: Claude Mythos Preview, and code execution: Claude Mythos Preview. Both models share reasoning mode, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
Pricing coverage is uneven: Claude Mythos Preview has $25/1M input tokens and Grok 4.20 Reasoning has no token price sourced yet. Provider availability is 2 tracked routes versus 0. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Claude Mythos Preview when coding workflow support and broader provider choice are central to the workload. Choose Grok 4.20 Reasoning when provider fit are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Is Claude Mythos Preview or Grok 4.20 Reasoning open source?
Claude Mythos Preview is listed under Proprietary. Grok 4.20 Reasoning 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 Grok 4.20 Reasoning?
Claude Mythos Preview has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for multimodal input, Claude Mythos Preview or Grok 4.20 Reasoning?
Claude Mythos Preview has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for reasoning mode, Claude Mythos Preview or Grok 4.20 Reasoning?
Both Claude Mythos Preview and Grok 4.20 Reasoning expose reasoning mode. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Which is better for function calling, Claude Mythos Preview or Grok 4.20 Reasoning?
Claude Mythos Preview has the clearer documented function calling signal in this comparison. If function calling is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run Claude Mythos Preview and Grok 4.20 Reasoning?
Claude Mythos Preview is available on Anthropic and Microsoft Foundry. Grok 4.20 Reasoning is available on the tracked providers still being sourced. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-16. Data sourced from public model cards and provider documentation.