Grok 4 Fast — xAI | Modeldex

Grok 4 Fast

Active

High-speed variant of Grok 4.

Updated 3 days agoStructured data from Modeldex catalog

Agentic

Knowledge cutoff

Sep 30, 2025(7 months ago)

API release

Sep 19, 2025(7 months ago)

Not enough benchmark coverage yet for an Intelligence Index — needs at least 3 results across 2 categories.

History

Grok 4 Fast became available via the xAI API on 2025-09-19.

Training & availability

Training data has a knowledge cutoff of 2025-09-30 — information about events after that date is unlikely to appear in the model's responses. xAI has not released the underlying model weights — access is via their hosted API only.

Capabilities

Input modalities: text.

Recommended for: agentic.

Limitations

Text-only — cannot process images, audio, or video inputs.

Quick start

Minimal example using the OpenRouter API. Copy, paste, replace the key.

from openai import OpenAI

client = OpenAI(
    base_url="https://openrouter.ai/api/v1",
    api_key="sk-or-...",
)
resp = client.chat.completions.create(
    model="xai/grok-4-fast",
    messages=[{"role": "user", "content": "Explain quantum computing in one sentence."}],
)
print(resp.choices[0].message.content)

Cost calculator

Estimate your monthly bill. Presets are typical workload sizes.

Input tokens / month5.0M

@ $0.2/1M

Output tokens / month2.0M

@ $0.5/1M

Input cost

5.0M × $0.2/1M

Output cost

2.0M × $0.5/1M

Total / month

$24 / year

Providers & performance

1 provider

Multi-provider inference routes for this model — sorted by throughput. Latency is time-to-first-token; throughput is output tokens per second. Data from OpenRouter, measured over the last 30 minutes.

Provider	Throughput	Latency (TTFT)	Input $ / 1M	Output $ / 1M	Context	Quant	Supports
xAI	33tok/s	504ms	$0.2	$0.5	2.0M	—	tools · json

Integrations & tooling support

Tool calling: Supported
Structured outputs: Not supported

Price vs quality

Budget pricing

Priced low — good for high-volume tasks. Quality tier pending more benchmark coverage.