Grok 4.1 Fast

xAIbudget

xAI's efficient budget model with the same 2M context window as Grok 4.20 at a fraction of the cost. Fast reasoning at $0.20/$0.50 makes it one of the cheapest models with genuine reasoning capability. Ideal for high-volume analytical workloads.

Released 2025-11-20Knowledge cutoff: 2025-09

Medium confidence|Updated 86d ago|78% source confidence

Specifications

Context Window

2M tokens

Max Output

32K tokens

Input Price

$0.200 / 1M tokens

Output Price

$0.500 / 1M tokens

Latency Tier

Ultra Fast (speed score: 9/10)

Capability Profile

Cost Efficiency

9.5/10

Long Context

9/10

Speed

9/10

Reasoning

7/10

Structured Output

7/10

Instruction Following

7/10

Conversational

7/10

Coding

6.5/10

Factuality

6.5/10

Tool Use

6.5/10

Creativity

6/10

Safety & Enterprise

5.5/10

Multimodal

1/10

Feature Support

Vision No

Audio In No

Audio Out No

Video No

Image Generation No

Image Editing No

Function Calling Yes

JSON Mode Yes

Structured Output Yes

Streaming Yes

Reasoning Yes

Realtime No

Computer Use No

Web Search No

Best Use Cases

High-volume text analysis over very long documents at minimal cost

Budget reasoning tasks where some depth matters but not full frontier quality

Long document summarization and extraction leveraging 2M context

Triage and classification with light reasoning at scale

Not Ideal For

Multimodal tasks (text only)

Complex coding requiring high precision

Enterprise-critical applications with safety requirements

Tasks requiring the best possible quality regardless of cost

Strengths

2M context window at $0.20/M input — extraordinary value for long-context work

Fast inference with reasonable reasoning capability

One of the cheapest models with genuine analytical depth

Good at straightforward extraction and summarization tasks

Weaknesses

Text only — no vision or multimodal

Significant quality gap vs Grok 4.20 on complex reasoning

Safety alignment is minimal

Coding output is functional but error-prone on complex tasks

Smaller community and fewer integrations than budget models from OpenAI or Google

Edge Cases & Notes

2M context is available but quality degrades more than Grok 4.20 at extreme lengths

More permissive content policy inherited from xAI's approach

Best used for tasks where the long context is the primary value driver

Provider Notes

Available through the xAI API. Good value for teams that need massive context at low cost. Consider GPT-5.4-nano or Gemini 2.5 Flash Lite for general budget tasks.

Benchmarks

MMLU79.5%

HumanEval75%

Arena Elo1190

Benchmark Notes

Solid for a budget model. Long-context benchmarks are its standout feature. General quality is comparable to GPT-4o-mini era models but with much larger context.

Research Meta

Last Evaluated

2026-03-01

Source Confidence

78%

Evaluation Method

LMSYS Arena, long-context benchmarks, cost-quality analysis

Needs Re-evaluation

Sources

xAI Grok 4.1 Fast documentation
LMSYS Chatbot Arena
Independent benchmarks

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