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 pricing, Grok 4 Fast Reasoning costs $1.25/1M input tokens versus $5/1M 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.
Grok 4 Fast Reasoning is ~300% cheaper at $1.25/1M; pay for Claude Opus 4.6 only for coding workflow support.
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 | $2.50/1M tokens |
| Provider routes | 6 tracked | 2 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Claude Opus 4.6 has broader tracked provider coverage for fallback and procurement flexibility.
- Claude Opus 4.6 uniquely exposes Function calling, Tool use, and Structured outputs 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.
- Grok 4 Fast Reasoning has the lower cheapest tracked output price at $2.50/1M tokens.
- 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
$1,625
Cheapest tracked route/tier: xAI Console
Estimated monthly gap: $8,625. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on Microsoft Foundry; start route-level A/B tests there.
- Grok 4 Fast Reasoning is $22.50/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Function calling, Tool use, and Structured outputs before moving production traffic.
- Provider overlap exists on Microsoft Foundry; start route-level A/B tests there.
- Claude Opus 4.6 is $22.50/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Claude Opus 4.6 adds Function calling, Tool use, and Structured outputs 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 |
| Commercial use | Commercial use with conditions | Commercial use with conditions |
| Knowledge cutoff | 2025-12 | - |
Pricing and availability
| Pricing attribute | Claude Opus 4.6 | Grok 4 Fast Reasoning |
|---|---|---|
| Input price | $5/1M tokens | $1.25/1M tokens |
| Output price | $25/1M tokens | $2.50/1M tokens |
| Providers |
Capabilities
| Capability | Claude Opus 4.6 | Grok 4 Fast Reasoning |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | Yes |
| Function calling | Yes | No |
| 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
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on 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 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.
For cost, Claude Opus 4.6 lists $5/1M input and $25/1M output tokens on the cheapest tracked provider, while Grok 4 Fast Reasoning lists $1.25/1M input and $2.50/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Grok 4 Fast Reasoning lower by about $9.38 per million blended tokens. Availability is 6 providers versus 2, so concentration risk also matters.
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, larger context windows, and lower 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 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.
Which is cheaper, Claude Opus 4.6 or Grok 4 Fast Reasoning?
Grok 4 Fast Reasoning is cheaper on tracked token pricing. Claude Opus 4.6 costs $5/1M input and $25/1M output tokens. Grok 4 Fast Reasoning costs $1.25/1M input and $2.50/1M output tokens. Provider discounts or batch pricing can still change the final bill.
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.
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: 2026-05-22. Data sourced from public model cards and provider documentation.