Claude Opus 4.6 vs Grok 4 Fast Reasoning
Claude Opus 4.6 (2026) and Grok 4 Fast Reasoning (2025) 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 2M-token context window. On LMArena Text Arena - Creative Writing, Claude Opus 4.6 leads by 106 pts. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Claude Opus 4.6 is safer overall; choose Grok 4 Fast Reasoning when long-context analysis matters.
Decision scorecard
Local evidence first| Signal | Claude Opus 4.6 | Grok 4 Fast Reasoning |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | reasoning-heavy apps, multimodal apps, and long-context analysis |
| Decision fit | Coding, RAG, and Agents | Long context and Vision |
| Context window | 1M | 2M |
| Cheapest output | $25/1M tokens | - |
| Provider routes | 6 tracked | 2 tracked |
| Shared benchmarks | LMArena Text Arena - Creative Writing leader | 1 shared |
Decision tradeoffs
- Claude Opus 4.6 holds a shared-benchmark lead on LMArena Text Arena - Creative Writing, ahead by 106 points.
- Claude Opus 4.6 has broader tracked provider coverage for fallback and route flexibility.
- Claude Opus 4.6 uniquely exposes JSON / Tool use, Structured outputs, and Code execution in local model data.
- Local decision data tags Claude Opus 4.6 for Coding, RAG, and Agents.
- Grok 4 Fast Reasoning has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Local decision data tags Grok 4 Fast Reasoning for Long context and Vision.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Claude Opus 4.6
$10,250
Cheapest tracked route/tier: Anthropic
Grok 4 Fast 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
- Provider overlap exists on Microsoft Foundry; start route-level A/B tests there.
- Check replacement coverage for JSON / Tool use, Structured outputs, and Code execution before moving production traffic.
- Provider overlap exists on Microsoft Foundry; start route-level A/B tests there.
- Claude Opus 4.6 adds JSON / Tool use, Structured outputs, and Code execution in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-02-05 | 2025-09-01 |
| Context window | 1M | 2M |
| Parameters | — | — |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Weights | Not released | Not released |
| Code | Unknown | Unknown |
| Commercial use | Restricted | Restricted |
| 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 | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | Yes |
| JSON / Tool use | Yes | No |
| Structured outputs | Yes | No |
| Code execution | Yes | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
| Benchmark | Claude Opus 4.6 | Grok 4 Fast Reasoning |
|---|---|---|
| LMArena Text Arena - Creative Writing | 1484.0 | 1378.0 |
Deep dive
On shared benchmark coverage, LMArena Text Arena - Creative Writing has Claude Opus 4.6 at 1484 and Grok 4 Fast Reasoning at 1378, with Claude Opus 4.6 ahead by 106 points. The largest visible gap is 106 points on LMArena Text Arena - Creative Writing, 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 differs most on JSON / Tool use: Claude Opus 4.6, JSON / Tool use: Claude Opus 4.6, structured outputs: Claude Opus 4.6, and code execution: Claude Opus 4.6. Both models share vision, multimodal input, and 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 listed. Provider availability is 6 listed routes versus 2. 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 long-context analysis and larger context windows 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 Opus 4.6 or Grok 4 Fast Reasoning?
Grok 4 Fast Reasoning supports 2M tokens, while Claude Opus 4.6 supports 1M tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
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?
Both Claude Opus 4.6 and Grok 4 Fast Reasoning expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Which is better for multimodal input, Claude Opus 4.6 or Grok 4 Fast Reasoning?
Both Claude Opus 4.6 and Grok 4 Fast Reasoning expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
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.
Where can I run Claude Opus 4.6 and Grok 4 Fast Reasoning?
Claude Opus 4.6 is available on Anthropic, AWS Bedrock, GCP Vertex AI, Microsoft Foundry, and OpenRouter. Grok 4 Fast Reasoning is available on Microsoft Foundry and xAI Console. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-10-17. Data sourced from public model cards and provider documentation.