Grok-4.1 Fast Reasoning vs Kimi K2.8 Preview
Comparing Grok-4.1 Fast Reasoning and Kimi K2.8 Preview across benchmarks, pricing, and capabilities.
xAI · Moonshot AI · Updated for 2026
Which is better?
Grok-4.1 Fast Reasoning and Kimi K2.8 Preview trade strengths across price, capabilities, and technical limits. The better choice depends on the workload.
Grok-4.1 Fast Reasoning also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.
Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.
Choose Grok-4.1 Fast Reasoning
- you process long inputs — it offers a 2,000,000 token context window
Choose Kimi K2.8 Preview
- you want the most recent training data — it shipped Sep 2026
At a glance
The differences that matter most.
Individual benchmarks
0 reported for Grok-4.1 Fast Reasoning · 0 for Kimi K2.8 Preview
Grok-4.1 Fast Reasoning and Kimi K2.8 Previewdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.
Human preference
Blind head-to-head votes and playground preference scores
Context Window
Maximum input and output token capacity
Grok-4.1 Fast Reasoning accepts 2,000,000 input tokens compared to Kimi K2.8 Preview's 1,048,576 tokens. Only Grok-4.1 Fast Reasoning specifies output context (30,000 tokens).
Input capabilities
Documented input modalities across available providers
Both Grok-4.1 Fast Reasoning and Kimi K2.8 Preview support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
Grok-4.1 Fast Reasoning
Kimi K2.8 Preview
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
Grok-4.1 Fast Reasoning was released on 2025-11-17, while Kimi K2.8 Preview was released on 2026-09-11.
Kimi K2.8 Preview is 10 months newer than Grok-4.1 Fast Reasoning.
Nov 17, 2025
10 months ago
Sep 11, 2026
1 weeks ago
9mo newerKnowledge Cutoff
When training data ends
Neither model specifies a knowledge cutoff date.
Unable to compare the recency of their training data.
Provider Availability
Grok-4.1 Fast Reasoning is available from xAI. Kimi K2.8 Preview is available from Moonshot AI.
Grok-4.1 Fast Reasoning
Kimi K2.8 Preview
Outputs Comparison
Judge for yourself.
Run your own prompts against Grok-4.1 Fast Reasoning and Kimi K2.8 Preview side-by-side, then vote on the output you prefer.
FAQ
Common questions about Grok-4.1 Fast Reasoning vs Kimi K2.8 Preview.