Aion 3.5 Mini
GPT-6 Luna
- Context
- 2Mtokens
- Released
- 10mo ago
Fast Grok model for responsive chat, reasoning, and tool-assisted work
- Multimodal model
- Accepts images, audio, video
- 2M context
- Reasoning
- Tools
How it compares
Level
LightweightThe lab's smallest, cheapest and lowest-latency hosted line, built for high volume and simple tasks.
Lightweight models from other labs
Vs. your stack
Add the models you use to see how this one compares.
Sign inAdditional source evidence
- Source model
- xai/grok-4-fast-reasoning
- Source family
- grok
- Last updated
- 2025-12-18
- Model context
- 2M
- Model output limit
- 2M
- Open weights
- No
- File attachments
- Yes
- Reasoning
- Yes
- Tool calling
- Yes
- Temperature control
- Yes
Complete source record (JSON)
{
"id": "xai/grok-4-fast-reasoning",
"name": "X-Ai/Grok-4-Fast-Reasoning",
"description": "Fast Grok model for responsive chat, reasoning, and tool-assisted work",
"family": "grok",
"last_updated": "2025-12-18",
"attachment": true,
"reasoning": true,
"tool_call": true,
"temperature": true,
"modalities": {
"input": [
"text",
"image",
"audio",
"video"
],
"output": [
"text"
]
},
"limit": {
"context": 2000000,
"output": 2000000
},
"release_date": "2025-12-18",
"open_weights": false
}Frequently asked questions
Capabilities and specs
The context window is 2M tokens (2,000,000), and the maximum output is 2M tokens (2,000,000).
Yes to images, audio and video, plus text. PDFs are not listed as a supported input.
Yes, tool calling (function calling) is supported.
Yes, a reasoning mode is supported.
Quality and benchmarks
On Arena WebDev it holds rank 155 with score 1162. On Arena Text it holds rank 161 with score 1405.
The closest alternatives are ERNIE 5.0 by Baidu, Composer 1 by Cursor and Composer 1.5 by Cursor. They were matched on model kind and release date, with no comparable price.
ERNIE 5.0X-Ai/Grok-4-Fast-Reasoning vs ERNIE 5.0Composer 1X-Ai/Grok-4-Fast-Reasoning vs Composer 1Composer 1.5X-Ai/Grok-4-Fast-Reasoning vs Composer 1.5
The best open-weight alternative is Kimi K3, ranked 19 on Arena Text. X-Ai/Grok-4-Fast-Reasoning itself is closed.
Versions and lineage
The listed facts show no difference: both have a context of 2M tokens (2,000,000) and both were released December 18, 2025.
X-Ai/Grok-4-Fast-Non-ReasoningX-Ai/Grok-4-Fast-Reasoning vs X-Ai/Grok-4-Fast-Non-Reasoning
Licensing and access
No, X-Ai/Grok-4-Fast-Reasoning is closed.
Basics
X-Ai/Grok-4-Fast-Reasoning was made by xAI and released on December 18, 2025.
Generated from Vertical Tabs data, updated November 12, 2026.
Discussion
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