Grok 4 Fast Reasoning vs Kimi K2 Thinking Turbo
Grok 4 Fast Reasoning (2025) and Kimi K2 Thinking Turbo (2025) are frontier reasoning models from xAI and Moonshot AI. Grok 4 Fast Reasoning ships a 2m-token context window, while Kimi K2 Thinking Turbo ships a 262k-token context window. On pricing, Kimi K2 Thinking Turbo costs $1.15/1M input tokens versus $1.25/1M 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.
Grok 4 Fast Reasoning fits 8x more tokens; pick it for long-context work and Kimi K2 Thinking Turbo for tighter calls.
Decision scorecard
Local evidence first| Signal | Grok 4 Fast Reasoning | Kimi K2 Thinking Turbo |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and long-context analysis | general production evaluation |
| Decision fit | Long context and Vision | Long context |
| Context window | 2m | 262k |
| Cheapest output | $2.50/1M tokens | $8/1M tokens |
| Provider routes | 2 tracked | 1 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- 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.
- Grok 4 Fast Reasoning has broader tracked provider coverage for fallback and procurement flexibility.
- Grok 4 Fast Reasoning uniquely exposes Vision, Multimodal, and Reasoning in local model data.
- Local decision data tags Grok 4 Fast Reasoning for Long context and Vision.
- Local decision data tags Kimi K2 Thinking Turbo for Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Grok 4 Fast Reasoning
$1,625
Cheapest tracked route/tier: xAI Console
Kimi K2 Thinking Turbo
$2,920
Cheapest tracked route/tier: Vercel AI Gateway
Estimated monthly gap: $1,295. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for Grok 4 Fast Reasoning and Kimi K2 Thinking Turbo; plan for SDK, billing, or endpoint changes.
- Kimi K2 Thinking Turbo is $5.50/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Vision, Multimodal, and Reasoning before moving production traffic.
- No overlapping tracked provider route is sourced for Kimi K2 Thinking Turbo and Grok 4 Fast Reasoning; plan for SDK, billing, or endpoint changes.
- Grok 4 Fast Reasoning is $5.50/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Grok 4 Fast Reasoning adds Vision, Multimodal, and Reasoning in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-09-01 | 2025-11-06 |
| Context window | 2m | 262k |
| Parameters | — | 1T (32B active) |
| Architecture | decoder only | - |
| License | Proprietary | MIT(OSI) |
| Openness | Proprietary | Open source |
| Commercial use | Commercial use with conditions | Commercial use allowed |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Grok 4 Fast Reasoning | Kimi K2 Thinking Turbo |
|---|---|---|
| Input price | $1.25/1M tokens | $1.15/1M tokens |
| Output price | $2.50/1M tokens | $8/1M tokens |
| Providers |
Capabilities
| Capability | Grok 4 Fast Reasoning | Kimi K2 Thinking Turbo |
|---|---|---|
| Vision | Yes | No |
| Multimodal | Yes | No |
| Reasoning | Yes | No |
| Function calling | No | No |
| Tool use | No | No |
| Structured outputs | No | No |
| Code execution | No | 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 vision: Grok 4 Fast Reasoning, multimodal input: Grok 4 Fast Reasoning, and reasoning mode: Grok 4 Fast Reasoning. Both models share the core language-model surface, 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, Grok 4 Fast Reasoning lists $1.25/1M input and $2.50/1M output tokens on the cheapest tracked provider, while Kimi K2 Thinking Turbo lists $1.15/1M input and $8/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Grok 4 Fast Reasoning lower by about $1.58 per million blended tokens. Availability is 2 providers versus 1, so concentration risk also matters.
Choose Grok 4 Fast Reasoning when reasoning depth, larger context windows, and broader provider choice are central to the workload. Choose Kimi K2 Thinking Turbo when provider fit 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. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions.
FAQ
Which has a larger context window, Grok 4 Fast Reasoning or Kimi K2 Thinking Turbo?
Grok 4 Fast Reasoning supports 2m tokens, while Kimi K2 Thinking Turbo supports 262k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Grok 4 Fast Reasoning or Kimi K2 Thinking Turbo?
Grok 4 Fast Reasoning is cheaper on tracked token pricing. Grok 4 Fast Reasoning costs $1.25/1M input and $2.50/1M output tokens. Kimi K2 Thinking Turbo costs $1.15/1M input and $8/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Grok 4 Fast Reasoning or Kimi K2 Thinking Turbo open source?
Grok 4 Fast Reasoning is listed under Proprietary. Kimi K2 Thinking Turbo is listed under MIT. 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, Grok 4 Fast Reasoning or Kimi K2 Thinking Turbo?
Grok 4 Fast Reasoning 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, Grok 4 Fast Reasoning or Kimi K2 Thinking Turbo?
Grok 4 Fast Reasoning 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.
Where can I run Grok 4 Fast Reasoning and Kimi K2 Thinking Turbo?
Grok 4 Fast Reasoning is available on Microsoft Foundry and xAI Console. Kimi K2 Thinking Turbo is available on Vercel AI Gateway. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-06-04. Data sourced from public model cards and provider documentation.