Grok 3 vs Grok 4 API: What Changed and When to Upgrade

Grok 3 vs Grok 4 API: What Changed and When to Upgrade#

xAI's Grok has gone from a Twitter novelty to a serious frontier model. Grok 4 launched in early 2026 with significant improvements over Grok 3 — but should you upgrade your integration? This guide covers everything developers need to know.

Grok 3 vs Grok 4: The Quick Summary#

What Is Grok 4?#

Grok 4 is xAI's fourth-generation language model, available in two main variants:

1. Grok 4 — Full capability model with extended reasoning support
2. Grok 4.1 Fast — Optimized for speed and cost, uses MoE architecture to deliver faster inference at lower cost

Both are available via the xAI API (native) and through aggregators like Crazyrouter, which provides OpenAI-compatible access to Grok 4.

Key Improvements in Grok 4#

1. Better Reasoning and Math#

Grok 4's biggest improvement is reasoning. In extended "think" mode, it approaches o3-level performance on math and logic problems. On MATH-500 (competition math):

• Grok 3: 62.1%
• Grok 4 (standard): 74.4%
• Grok 4 Heavy (with thinking): 88.3%

2. Improved Code Generation#

HumanEval jumped from 71.3% → 79.8%. In practice this means:

• Better understanding of complex algorithmic problems
• Fewer hallucinated function signatures
• More accurate error handling suggestions
• Better at multi-file code refactoring

3. Faster Inference (Grok 4.1 Fast)#

Grok 4.1 Fast uses a Mixture of Experts architecture (only activating ~22B of 314B parameters per token), delivering:

• ~95 tokens/second (vs ~65 for Grok 3)
• ~450ms TTFT (vs ~700ms for Grok 3)
• 40% lower input token cost

4. Better Multimodal Understanding#

Image understanding improved significantly. Grok 4 can now:

• Read text in images (OCR)
• Understand charts and diagrams more accurately
• Handle multiple images in a single request
• Process screenshots for UI analysis

Grok 4 Pricing Breakdown#

Via Crazyrouter:

How to Access Grok 4 API#

Option 1: xAI Native API#

import anthropic  # xAI uses Anthropic-compatible SDK

client = anthropic.Anthropic(
    api_key="your-xai-api-key",
    base_url="https://api.x.ai/v1"
)

message = client.messages.create(
    model="grok-4-1-fast",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Explain Mixture of Experts architecture"}
    ]
)

print(message.content[0].text)

Option 2: Via Crazyrouter (OpenAI-Compatible)#

from openai import OpenAI

# Use the same OpenAI SDK you already know
client = OpenAI(
    api_key="your-crazyrouter-key",
    base_url="https://crazyrouter.com/v1"
)

response = client.chat.completions.create(
    model="grok-4-1-fast",
    messages=[
        {"role": "system", "content": "You are a helpful assistant."},
        {"role": "user", "content": "Write a Python function to parse JSON with error handling"}
    ],
    max_tokens=1024
)

print(response.choices[0].message.content)

Node.js Example#

import OpenAI from 'openai';

const client = new OpenAI({
  apiKey: process.env.CRAZYROUTER_API_KEY,
  baseURL: 'https://crazyrouter.com/v1',
});

async function askGrok4(question) {
  const response = await client.chat.completions.create({
    model: 'grok-4-1-fast',
    messages: [
      { role: 'user', content: question }
    ],
    temperature: 0.7,
    max_tokens: 2048,
  });
  
  return response.choices[0].message.content;
}

const answer = await askGrok4('What are the trade-offs of MoE vs dense transformer models?');
console.log(answer);

cURL#

curl https://crazyrouter.com/v1/chat/completions \
  -H "Authorization: Bearer your-crazyrouter-key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "grok-4-1-fast",
    "messages": [
      {"role": "user", "content": "Write a regex for validating email addresses"}
    ],
    "temperature": 0.3,
    "max_tokens": 512
  }'

Migration Guide: Grok 3 → Grok 4#

Upgrading is mostly a model name change. However, there are a few behavioral differences to test:

1. Update Model Name#

# Before
model = "grok-3"

# After (choose based on needs)
model = "grok-4-1-fast"   # 40% cheaper, 50% faster
# OR
model = "grok-4"           # Best quality
# OR  
model = "grok-4-heavy"     # Maximum reasoning

2. Test Output Length#

Grok 4 supports up to 16,384 output tokens (vs 8,192 for Grok 3). If you had workarounds for long outputs, you may be able to simplify them.

3. Function Calling Format#

Grok 4 improved function calling reliability. If you had retry logic for failed function calls, test whether you can simplify it:

# Grok 4 is more reliable with complex tool schemas
tools = [
    {
        "type": "function",
        "function": {
            "name": "search_database",
            "description": "Search the product database",
            "parameters": {
                "type": "object",
                "properties": {
                    "query": {"type": "string"},
                    "filters": {
                        "type": "object",
                        "properties": {
                            "category": {"type": "string"},
                            "price_max": {"type": "number"}
                        }
                    }
                },
                "required": ["query"]
            }
        }
    }
]

response = client.chat.completions.create(
    model="grok-4-1-fast",
    messages=[{"role": "user", "content": "Find laptops under $1000"}],
    tools=tools,
    tool_choice="auto"
)

4. Check Real-time Web Search (Grok-specific)#

If you're using Grok's real-time X/Twitter data access features via the native xAI API, these persist in Grok 4. Via Crazyrouter, standard completions are available without real-time search unless enabled.

When Should You NOT Upgrade?#

Stay on Grok 3 if:

• You're cost-sensitive and batch processing: Grok 4.1 Fast is actually cheaper, so this rarely applies
• You've fine-tuned prompts carefully for Grok 3: Some prompts need retuning due to different default behavior
• Your downstream systems parse Grok 3 output format: Test that Grok 4's slightly different formatting doesn't break parsing

Grok 4 vs Other Frontier Models#

Grok 4.1 Fast is particularly competitive for cost-sensitive, speed-critical applications. It's not the absolute best at any single task, but its price/performance ratio is excellent.

Frequently Asked Questions#

Q: Is Grok 4 better than Claude Opus 4.6? A: For most general tasks, Claude Opus 4.6 still leads in instruction following and nuanced reasoning. Grok 4 is closer to Claude Sonnet 4.5 in overall quality but faster.

Q: Can I use Grok 4 with the OpenAI Python SDK? A: Yes, via Crazyrouter. Set base_url="https://crazyrouter.com/v1" and use model="grok-4-1-fast".

Q: Does Grok 4 have a free tier? A: Grok 4 is available free to X Premium subscribers via the Grok.com interface. API access requires an xAI developer account or a Crazyrouter subscription.

Q: What's the difference between Grok 4 and Grok 4 Heavy? A: Grok 4 Heavy enables extended thinking/reasoning mode (like o3 or Kimi K2 Thinking), making it much stronger for math, logic, and complex coding problems — at 5× the cost.

Q: Should I use Grok 4.1 Fast or Grok 4? A: For most production use cases, Grok 4.1 Fast delivers 90% of Grok 4's quality at 40% lower input cost and 50% higher speed. Use Grok 4 full when you need maximum quality.

Summary#

Grok 4 represents a meaningful upgrade over Grok 3:

• 40% faster (Grok 4.1 Fast variant)
• 40% cheaper on input tokens
• Better coding (HumanEval: 71% → 80%)
• Better reasoning (especially Grok 4 Heavy)

For developers currently on Grok 3, migrating to Grok 4.1 Fast is a no-brainer — same or better quality, faster, cheaper.

Access Grok 4 alongside 300+ other models via Crazyrouter with OpenAI-compatible API and unified billing.

→ Try Grok 4 API at Crazyrouter