Grok 4.1 Fast

MultimodalRetiredUnavailable

by xAIgrok-4-1-fast

xAI's cost-efficient high-throughput model. 2M context, optional reasoning, optimized for agentic loops and real-time apps.

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Status: Unavailable
Context: 2,000,000 tokens
Max. output: 2,000,000 tokens
Input → output: Text + Image → Text
Developer: xAI
Updated: September 24, 2026

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About Grok 4.1 Fast

TL;DRAs of September 24, 2026

Grok 4.1 Fast is a model by xAI in the Multimodal category. Grok 4.1 Fast is currently not available on Railwail. The context window holds 2,000,000 tokens, and one response can be up to 2,000,000 tokens long.

Grok 4.1 Fast is xAI's cost-efficient variant for high-volume use, available in both reasoning and non-reasoning modes. 2M-token context window with 2M-token max output, vision input, and the same DeepSearch retrieval as 4.3. Designed for production agents, real-time chat, RAG pipelines and high-concurrency workloads where latency and cost dominate.

Background

About xAI

Founded 2023 · Palo Alto, USA

xAI was founded in March 2023 by Elon Musk together with senior researchers from DeepMind, OpenAI, Google Research, Microsoft Research and Tesla. The company's stated mission is to build maximally truth-seeking AI. The Grok lineage spans Grok 1 (open-source 314B MoE, November 2023), Grok 1.5, Grok 2, Grok 3 (February 2025), Grok 4 (mid-2025), Grok 4.1 Fast (late 2025), Grok 4.20 (early 2026) and Grok 4.3 (May 2026). The Fast variants are xAI's high-throughput, cost-optimized tier. xAI raised over $20 billion across multiple funding rounds and operates the Colossus supercluster in Memphis.

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Architecture

Decoder-only Transformer (cost-optimized, optional reasoning)

Grok 4.1 Fast was released as xAI's cost-efficient mid-tier model and refreshed throughout 2026. Architecturally it is a smaller and sparser variant of the Grok 4.x family, designed for high-throughput production workloads. The model is available in both reasoning and non-reasoning modes - developers can choose to enable test-time thinking on demand. Pretraining used the same multi-trillion-token mixture as Grok 4.3 (web text, code, X posts) on the Colossus supercluster, with heavy distillation from larger Grok teacher models. Post-training combined RLHF and reinforcement learning against verifiable rewards on math, code and tool-use trajectories. Grok 4.1 Fast supports a class-leading 2M-token context window with 2M-token max output, native vision input, and the upgraded DeepSearch retrieval agent. xAI positions it as the cost-efficient alternative to GPT-5.4 mini and Gemini 3 Flash.

Parameters: Undisclosed (smaller and sparser than Grok 4.3)
Context: 2,000,000 tokens

Capabilities

2M token context window and 2M token max output
Available in reasoning and non-reasoning modes
Vision input for images and screenshots
Native DeepSearch agent for X + web retrieval
Function calling and structured JSON output
Lowest per-token pricing in the Grok 4.x family
Strong throughput for production workloads
Available via xAI API and OpenRouter
Compatible with the same tool-use API as Grok 4.3
$175/month free API credits via data-sharing programme
Best for: production agents, real-time chat, RAG pipelines, high-concurrency workloads.

Training & license

Multi-trillion-token pretraining mixture of web text, code and X public posts; heavy distillation from larger Grok 4.x teacher models. Post-training combines RLHF and RL against verifiable rewards. Knowledge cutoff updated continuously through retrieval.

License: Proprietary commercial license via xAI API and partner platforms. Weights not publicly released.

Safety testing: Inherits the xAI Grok safety stack with the same lower-refusal-rate posture as Grok 4.3.

Known limitations

Below Grok 4.3 on the hardest reasoning and coding benchmarks
Lower refusal rate increases risk of harmful or biased output
Limited published third-party safety evaluations
Real-time retrieval depends heavily on the X corpus
Weights not released; reproducibility limited

Research papers

Pricing

Currently unavailable: this model has been deactivated. There is no price for this model at the moment, so it cannot be run.

API

Call Grok 4.1 Fast with your Railwail API key. Use this model ID in the request:

grok-4-1-fastAPI documentation Get an API key

No verified API example

The public API passes a different input format than this model needs. Use the playground above.

Specifications

Model ID: grok-4-1-fast
Developer: xAI
Category: Multimodal
Input: Text, Image
Output: Text
Context window: 2,000,000 tokens
Max. output: 2,000,000 tokens
Lifecycle: Retired
Model size: Undisclosed (smaller and sparser than Grok 4.3)
License: Proprietary commercial license via xAI API and partner platforms. Weights not publicly released.
Catalog entry updated: September 24, 2026

Use cases

What it is used for

Production chat and support agents
Real-time RAG and search pipelines
High-concurrency content moderation
Cost-sensitive coding assistants
DeepSearch-based question answering
X-platform analytics and trend detection
Long-document analysis with 2M context

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Frequently asked questions

What is Grok 4.1 Fast?

Grok 4.1 Fast is a model by xAI in the Multimodal category. It is listed on Railwail but cannot be run at the moment.

How much does Grok 4.1 Fast cost on Railwail?

Grok 4.1 Fast cannot be run on Railwail at the moment, so there is no current price. Available alternatives with prices are listed further down this page.

What is the context window of Grok 4.1 Fast?

The context window of Grok 4.1 Fast holds 2,000,000 tokens. One response can be up to 2,000,000 tokens long.

How fast is Grok 4.1 Fast?

There are not enough measured runs of Grok 4.1 Fast on Railwail yet to state a run time. It depends on the input, the settings and the load at the provider.

Is Grok 4.1 Fast better than BLIP?

That depends on the task. Grok 4.1 Fast (xAI) and BLIP (Salesforce) are both models in the Multimodal category. The comparison page shows their prices and specifications side by side.

Compare Grok 4.1 Fast and BLIP

Can Grok 4.1 Fast process images?

Yes. Grok 4.1 Fast accepts images as input in addition to text.

Can I use Grok 4.1 Fast right now?

Currently unavailable: this model has been deactivated. The page stays online; available alternatives from the same category are listed further down.

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