Claude Sonnet 4.6 Guide 2025: Features, API & Best Use Cases

What Is Claude Sonnet 4.6?

Claude Sonnet 4.6 (model ID: claude-sonnet-4-6) is Anthropic's primary production model as of 2025. It sits in the middle of the Claude lineup — faster than Opus, more capable than Haiku — and delivers the best quality-per-dollar ratio for most real-world tasks.

Key capabilities: 200,000 token context window (~150k words), multimodal vision (image analysis), tool use (function calling), computer use (desktop automation via API), and top SWE-bench coding scores. All Claude models, including Sonnet, are trained with Anthropic's Constitutional AI approach for consistent, safe behavior.

Claude Model Comparison (2025)

For most applications: start with Sonnet. Use Haiku for high-throughput pipelines where cost matters. Use Opus for tasks where your best answer is worth 5x the price.

API Quickstart

1. Go to console.anthropic.com and sign in
2. Navigate to API Keys and click Create Key
3. Copy your key — it starts with sk-ant-api03-
4. Add billing in the Billing section to go beyond the free trial credits

pip install anthropic

import anthropic

client = anthropic.Anthropic()  # uses ANTHROPIC_API_KEY env var

message = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    system="You are a helpful assistant specialized in Python.",
    messages=[
        {"role": "user", "content": "Write a function to flatten a nested list."}
    ]
)

print(message.content[0].text)
# Input tokens: {message.usage.input_tokens}
# Output tokens: {message.usage.output_tokens}

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "Hello, Claude!"}]
  }'

Best Use Cases for Claude Sonnet

Claude Sonnet vs GPT-4o vs Gemini 1.5 Pro

For a deep dive, see ChatGPT vs Claude. For full Anthropic API docs, see Anthropic API Guide.

System Prompt Tips for Sonnet