Claude 4 Stopped Working? Here's Exactly What to Do

Your Claude 4 API calls are failing. model not found. deprecated model. Your app is down. Here's the fastest path to fixing it — and saving up to 99% on API costs while you're at it.

Step 1: Identify the Error

When Claude 4 is deprecated, you'll see one of these error responses:

{
  "type": "error",
  "error": {
    "type": "not_found_error",
    "message": "model 'claude-4-opus' not found"
  }
}

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "model 'claude-sonnet-4' is deprecated and no longer available"
  }
}

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "model 'claude-4-opus' has been retired. Use 'claude-opus-4-8' instead"
  }
}

All three errors mean the same thing: the model name you're using no longer works. The fix is identical regardless of which error you see.

Step 2: Apply the Quick Fix

Find the model name in your code and replace it. That's it.

Python

# Before (broken)
client = anthropic.Anthropic()
message = client.messages.create(
    model="claude-4-opus",  # ← THIS IS THE PROBLEM
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello"}]
)

# After (fixed)
message = client.messages.create(
    model="claude-opus-4-8",  # ← FIXED
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello"}]
)

Node.js

// Before (broken)
const message = await anthropic.messages.create({
    model: 'claude-4-opus',  // ← THIS IS THE PROBLEM
    max_tokens: 1024,
    messages: [{ role: 'user', content: 'Hello' }]
});

// After (fixed)
const message = await anthropic.messages.create({
    model: 'claude-opus-4-8',  // ← FIXED
    max_tokens: 1024,
    messages: [{ role: 'user', content: 'Hello' }]
});

cURL

# Before (broken)
curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -d '{"model": "claude-4-opus", ...}'  # ← PROBLEM

# After (fixed)
curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -d '{"model": "claude-opus-4-8", ...}'  # ← FIXED

Step 3: Save Money While You're At It

You're already fixing the error — might as well cut your bill. Claude Opus 4.8 is the direct replacement, but there are 34 cheaper alternatives.

For a typical workload of 10M input + 2M output tokens per month:

• Claude 4 Opus: $300/month
• Claude Opus 4.8: $100/month (save $200)
• GPT-5.5: $45/month (save $255)
• DeepSeek V4 Pro: $6.09/month (save $294)

Step 4: If It's Still Not Working

If you've changed the model name and it's still failing, check these common issues:

1. Check your .env file

If you're using an environment variable for the model name, update it there too:

# .env
ANTHROPIC_MODEL=claude-opus-4-8  # NOT claude-4-opus

2. Check your config files

Look in config.json, settings.py, application.yml, or any other configuration file that might store the model name.

3. Check database records

If you store model names in a database (e.g., user preferences, saved configurations), update those records too:

-- Find stored Claude 4 references
SELECT * FROM configurations WHERE model LIKE '%claude-4%';

-- Update them
UPDATE configurations SET model = 'claude-opus-4-8' WHERE model = 'claude-4-opus';
UPDATE configurations SET model = 'claude-sonnet-4-6' WHERE model = 'claude-sonnet-4';

4. Clear your SDK cache

Some SDKs cache model lists. Restart your application or clear any cached model data.

5. Check rate limits

New model IDs may have different rate limits. If you're getting 429 errors after switching, check the rate limits documentation.

Complete Fix Checklist

Related Resources

• Claude Deprecation Calculator — Calculate your exact migration cost and savings
• Claude 4 Migration Tool — Compare all 34 alternatives with your exact usage
• Claude 4 API Errors — Every error code and how to fix it
• Claude 4 Deprecation Checklist — Complete 8-step migration checklist
• Claude 4 Migration Guide — Detailed code examples in Python, Node.js, and REST
• Claude 4 Deprecation FAQ — Every question answered about the deprecation
• Best Claude 4 Alternatives — Detailed comparison of all replacement options