Claude 4 Sonnet was retired on June 15, 2026. If you're still using it, your API calls are returning 404 errors. The good news: Claude Sonnet 4.6 is the official successor, it costs the same, and it has a 5x larger context window.
This comparison covers everything that changed between Claude 4 Sonnet and Claude Sonnet 4.6 — pricing, performance, context window, and how to migrate.
Quick Comparison
| Feature | Claude 4 Sonnet (DEAD) | Claude Sonnet 4.6 (SUCCESSOR) |
|---|---|---|
| Status | Retired June 15, 2026 | Active — current model |
| Input Cost | $3 / 1M tokens | $3 / 1M tokens (same) |
| Output Cost | $15 / 1M tokens | $15 / 1M tokens (same) |
| Context Window | 40K tokens | 200K tokens (5x larger) |
| API Format | Messages API | Messages API (identical) |
| Model ID | claude-4-sonnet |
claude-sonnet-4-6 |
| Reasoning | Good | Improved |
| Coding | Good | Better |
| Speed | Fast | Faster |
| Availability | None — 404 errors | 100% uptime SLA |
The Big Win: 5x Context Window
The most significant change is the context window: 200K tokens (up from 40K). That's 5x more text in a single prompt.
| Context Window | Claude 4 Sonnet | Claude Sonnet 4.6 |
|---|---|---|
| Tokens | 40,000 | 200,000 |
| Approximate Words | ~30,000 | ~150,000 |
| Approximate Pages | ~100 pages | ~500 pages |
| Code Files | ~20-30 files | ~100-150 files |
This means you can now process entire codebases, long documents, or complex multi-turn conversations without hitting context limits.
How to Migrate
Migration is a one-line change:
// Before (dead — returning 404)
model: "claude-4-sonnet"
// After (official successor)
model: "claude-sonnet-4-6"Same API, same SDK, same parameters, same prompts. Your existing code works without any other changes.
LangChain / LlamaIndex
# LangChain
chat = ChatAnthropic(model="claude-sonnet-4-6") # was "claude-4-sonnet"
# LlamaIndex
llm = Anthropic(model="claude-sonnet-4-6") # was "claude-4-sonnet"Find All References
grep -r "claude-4-sonnet" --include="*.js" --include="*.ts" --include="*.py" --include="*.json" .Ready to Migrate?
Use the APIpulse migration calculator to see your exact costs, then update your model ID. It takes 30 minutes.
Calculate Costs →Should You Switch to a Cheaper Alternative?
Sonnet 4.6 is the best drop-in replacement, but if cost is your primary concern, there are cheaper options:
| Model | Input / Output | vs Claude 4 Sonnet | Best For |
|---|---|---|---|
| Claude Sonnet 4.6 | $3 / $15 | Same price, 5x context | Drop-in replacement |
| GPT-5 Mini | $0.40 / $1.60 | 87% cheaper | Budget, high volume |
| Gemini 2.5 Flash | $0.15 / $0.60 | 96% cheaper | Google ecosystem |
| DeepSeek V4 Pro | $0.44 / $0.87 | 94% cheaper | Maximum savings |
| Llama 4 Maverick | $0.27 / $0.85 | 97% cheaper | Self-hosted, open source |
Use the APIpulse comparison tool to test these models against your specific use case.
Frequently Asked Questions
Will my prompts work the same on Sonnet 4.6?
Yes. Claude Sonnet 4.6 uses the same API format and responds to the same prompts. You may see slightly different outputs (it's a newer model), but your existing prompts will work without modification.
Is Sonnet 4.6 compatible with Claude 4 Sonnet SDKs?
Yes. The Anthropic SDK, OpenAI SDK (with Anthropic adapter), LangChain, LlamaIndex, and all other popular frameworks work with Sonnet 4.6. Only the model ID string changes.
What about Claude 4 Opus?
Claude 4 Opus is also retired. Its successor is Claude Opus 4.8 ($5/$25) — 67% cheaper with better performance. See the full Opus comparison.
Can I still use Claude 4 Sonnet through OpenRouter or Bedrock?
No. All providers have removed Claude 4 Sonnet from their available models. The model is gone from Anthropic's API entirely.
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