Claude AI Models Compared: Opus 4.6, Sonnet & Haiku Guide

Anthropic offers three tiers of Claude models, each optimized for different use cases. This guide covers the latest lineup including the newly released Claude Opus 4.6, helping you choose the right model for coding, agents, writing, or analysis.

Don't have time to read everything? Here's what you need to know:

Anthropic names their models after poetic forms, reflecting their approach to AI development. Each tier represents a different balance of capability, speed, and cost:

• Opus (a major musical composition) — The most capable, for complex work
• Sonnet (a 14-line poem) — Balanced and versatile
• Haiku (a 3-line poem) — Concise and fast

Version History

Claude models have evolved rapidly through multiple generations:

Benchmark Performance

• Terminal-Bench 2.0: Highest score (agentic coding)
• Humanity's Last Exam: Top performer (multidisciplinary reasoning)
• BrowseComp: Best performance (information retrieval)
• MRCR v2: 76% vs Opus 4.5's 18.5% (long-context retrieval)
• GDPval-AA: Outperforms GPT-5.2 by ~144 Elo points

When to Use Opus 4.6

Adaptive Thinking vs Extended Thinking

Opus 4.6 introduces adaptive thinking, which differs from extended thinking available in all models:

• Extended thinking: Available on all models. Always-on step-by-step reasoning before answering. You enable it explicitly in API calls.
• Adaptive thinking (Opus 4.6 only): The model autonomously decides when and how much to reason. Set effort levels (low/medium/high/max) and the model allocates reasoning dynamically per task.

When to Use Sonnet 4.5

When to Use Haiku 4.5

Quality Comparison (Simplified)

Claude models use token-based pricing. A token is roughly 4 characters or ¾ of a word.

Prompt Caching

Anthropic offers prompt caching to reduce costs for repeated context like system prompts:

• 5-minute cache write: 1.25x base input price
• 1-hour cache write: 2x base input price
• Cache read: 0.1x base input price (up to 90% savings)

Cost Optimization Tips

• Use model routing: Send simple queries to Haiku, complex ones to Sonnet/Opus
• Use Batch API: 50% off for non-time-sensitive workloads
• Cache system prompts: Up to 90% savings on repeated context
• Optimize prompts: Shorter, clearer prompts reduce token usage
• Start with Haiku: Test if it meets your quality needs before upgrading

Model IDs

Use these identifiers when calling the Anthropic API:

# Current models
Opus 4.6:   claude-opus-4-6
Sonnet 4.5: claude-sonnet-4-5-20250929
Haiku 4.5:  claude-haiku-4-5-20251001

# Aliases (always point to latest)
claude-sonnet-4-5
claude-haiku-4-5

Basic API Call (Python)

import anthropic

client = anthropic.Anthropic()
# Using Sonnet 4.5 (recommended default)
message = client.messages.create(
model="claude-sonnet-4-5-20250929",
max_tokens=1024,
messages=[
{"role": "user", "content": "Explain quantum computing"}
]
)
print(message.content[0].text)

Using Adaptive Thinking (Opus 4.6)

# Opus 4.6 adaptive thinking with effort control
message = client.messages.create(
model="claude-opus-4-6",
max_tokens=16384,
thinking={
"type": "enabled",
"budget_tokens": 10000
},
messages=[
{"role": "user", "content": "Analyze this codebase architecture..."}
]
)

Model Routing Pattern

def choose_model(task_complexity: str) -> str:
"""Select model based on task complexity."""
models = {
"simple": "claude-haiku-4-5-20251001",      # Fast, cheap
"moderate": "claude-sonnet-4-5-20250929",    # Balanced
"complex": "claude-opus-4-6",                # Best quality
"agentic": "claude-opus-4-6"                 # Multi-step agents
}
return models.get(task_complexity, models["moderate"])

1M Context Window (Beta)

# Enable 1M token context for Opus 4.6 or Sonnet 4.5
message = client.messages.create(
model="claude-opus-4-6",
max_tokens=8192,
betas=["context-1m-2025-08-07"],
messages=[
{"role": "user", "content": very_long_document + "\n\nSummarize this."}
]
)

Choosing the right Claude model depends on your specific needs:

• Default choice: Start with Sonnet 4.5 — it handles 90% of use cases well
• Agentic and complex work: Upgrade to Opus 4.6 for multi-step workflows, deep analysis, or large codebases
• High volume: Use Haiku 4.5 for chatbots, classification, or cost-sensitive applications

With Opus 4.6, Anthropic has pushed the frontier on agentic capabilities and long-context processing while keeping pricing accessible. The 1M token context window and agent teams open up entirely new use cases that were previously impractical.