xAI · Released Dec 18, 2025Grok 4 Fast Reasoning
Fast Grok model for responsive chat, reasoning, and tool-assisted work.
- Capability
- —No ECI score yet
- Input
- $0.20per 1M tokens
- Output
- $0.50per 1M tokens
- Context
- 2M2M max output
What it costs
- Input
- $0.20per million tokens
- Output
- $0.50per million tokens
- Blended (3:1)
- $0.275cheaper than 70% of priced models
Typical monthly bills
| Monthly usage | Estimated cost |
|---|---|
| Side project2M input + 0.5M output tokens | $0.65 |
| Team assistant25M input + 5M output tokens | $7.50 |
| Production app250M input + 50M output tokens | $75.00 |
Median of 4 paid API providers on models.dev.
Independent benchmarks
Epoch AI has not published a Capabilities Index score for Grok 4 Fast Reasoning yet.
The details
- Lab
- xAI
- Released
- Dec 18, 2025
- Context window
- 2,000,000 tokens
- Max output
- 2,000,000 tokens
- Inputs
- Text, Images, Audio, Video
- Output
- Text
- Reasoning
- Always on
- Tool calling
- Yes
- Structured output
- No
- Weights
- Proprietary
- Availability
- 5 API providerslisted on models.dev
More from xAI
About Grok 4 Fast Reasoning
How much does Grok 4 Fast Reasoning cost?
Grok 4 Fast Reasoning costs $0.20 input / $0.50 output per million tokens (median across 4 API providers). At a 3:1 input-to-output mix that is $0.275 per million tokens, cheaper than 70% of the 445 priced models we track.
What is the context window of Grok 4 Fast Reasoning?
Grok 4 Fast Reasoning accepts up to 2,000,000 tokens per request and can write up to 2,000,000 tokens in one response.
How good is Grok 4 Fast Reasoning?
Epoch AI has not published a Capabilities Index score for Grok 4 Fast Reasoning yet.
Is Grok 4 Fast Reasoning open source?
No. Grok 4 Fast Reasoning is proprietary; you use it through an API or partner platforms.
What inputs does Grok 4 Fast Reasoning support?
Grok 4 Fast Reasoning accepts text, images, audio and video and replies in text. It is a reasoning model, supports tool calling.
When was Grok 4 Fast Reasoning released?
xAI released Grok 4 Fast Reasoning on Dec 18, 2025.
What are the best alternatives to Grok 4 Fast Reasoning?
The closest current models from other labs on capability, price and release date are GLM-4.6V-Flash (Z.ai (Zhipu), $0.161 / $0.559), Jamba Mini (AI21 Labs, $0.20 / $0.40), Sarvam 105B (Sarvam AI, $0.158 / $0.632) and Solar Pro 3 (Upstage, $0.25 / $0.25).