Claude Opus 4.6 vs Grok 4 Fast Reasoning
Claude Opus 4.6 (2026) and Grok 4 Fast Reasoning (2026) are frontier-tier reasoning models from Anthropic and xAI. Claude Opus 4.6 ships a 1M-token context window, while Grok 4 Fast 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 Fast Reasoning is safer overall; choose Claude Opus 4.6 when coding workflow support matters.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-02-05 | 2026-03-01 |
| Context window | 1M | — |
| Parameters | — | — |
| Architecture | decoder only | decoder only |
| License | Proprietary | Proprietary |
| Knowledge cutoff | 2025-12 | - |
Pricing and availability
| Pricing attribute | Claude Opus 4.6 | Grok 4 Fast Reasoning |
|---|---|---|
| Input price | $5/1M tokens | - |
| Output price | $25/1M tokens | - |
| Providers |
Capabilities
| Capability | Claude Opus 4.6 | Grok 4 Fast 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 Opus 4.6, multimodal input: Claude Opus 4.6, function calling: Claude Opus 4.6, tool use: Claude Opus 4.6, structured outputs: Claude Opus 4.6, and code execution: Claude Opus 4.6. 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 Opus 4.6 has $5/1M input tokens and Grok 4 Fast Reasoning has no token price sourced yet. Provider availability is 4 tracked routes versus 1. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Claude Opus 4.6 when coding workflow support and broader provider choice are central to the workload. Choose Grok 4 Fast 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.
FAQ
Is Claude Opus 4.6 or Grok 4 Fast Reasoning open source?
Claude Opus 4.6 is listed under Proprietary. Grok 4 Fast 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 Opus 4.6 or Grok 4 Fast Reasoning?
Claude Opus 4.6 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 Opus 4.6 or Grok 4 Fast Reasoning?
Claude Opus 4.6 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 Opus 4.6 or Grok 4 Fast Reasoning?
Both Claude Opus 4.6 and Grok 4 Fast 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 Opus 4.6 or Grok 4 Fast Reasoning?
Claude Opus 4.6 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 Opus 4.6 and Grok 4 Fast Reasoning?
Claude Opus 4.6 is available on OpenRouter, Anthropic, AWS Bedrock, and GCP Vertex AI. Grok 4 Fast Reasoning is available on Microsoft Foundry. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-11. Data sourced from public model cards and provider documentation.