Grok 4.20 Fast

xAIgrok-4.20-fast

Context window1,000,000 tokens

StreamingJSON modeTool callingVisionLong context

Maximum output: 131,000 tokens.

Pricing

Input	Output	Cached input	Cache write
$1.25 / MTok	$2.50 / MTok	$0.20 / MTok	$1.25 / MTok

Typical request (5K input / 1K output tokens): ~$0.0088. Live pricing.

Use this model

Set up your SDK client, then run:

const completion = await client.chat.completions.create({
  model: "grok-4.20-fast",
  messages: [{ role: "user", content: "Explain edge caching in one paragraph." }],
});

console.log(completion.choices[0].message.content);

completion = client.chat.completions.create(
    model="grok-4.20-fast",
    messages=[{"role": "user", "content": "Explain edge caching in one paragraph."}],
)

print(completion["choices"][0]["message"]["content"])

curl https://www.ninjachat.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $NINJACHAT_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"grok-4.20-fast","messages":[{"role":"user","content":"Explain edge caching in one paragraph."}]}'

Supported parameters

messagestemperaturemax_completion_tokenstop_pstopfrequency_penaltypresence_penaltyseedstreamuserroutingtoolstool_choiceresponse_formatimage_url content parts

Send only parameters from this list. routing.require_parameters (default true) skips any provider rail that cannot honor every requested parameter, so requests keep the behavior you asked for.

Routing & fallbacks

Pin grok-4.20-fast with model when you want this model’s behavior, or list it in an ordered models array. With ninja/auto first, the router’s top pick runs first and grok-4.20-fast is the explicit fallback; ninja/auto acts as the router only when it is the first entry.

{
  "models": [
    "ninja/auto",
    "grok-4.20-fast"
  ],
  "messages": [
    {
      "role": "user",
      "content": "Explain edge caching in one paragraph."
    }
  ],
  "routing": {
    "allow_fallbacks": true
  }
}

You are billed at the resolved model’s token rates, and only for the successful execution.

Check current availability and limits

TypeScript SDK

const model = await client.models.retrieve("grok-4.20-fast");

if (!model.servable) throw new Error("grok-4.20-fast is temporarily unavailable");

console.log({
  contextWindow: model.contextWindow,
  maxOutputTokens: model.maxOutputTokens,
  capabilities: model.capabilities,
  supportedParameters: model.supportedParameters,
  pricing: model.pricing,
  providers: model.providers,
});

Guides: Text generation · Fallbacks · Smart routing · Pricing · All models

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