Claude 4 API Errors After June 15: How to Fix Them

Getting model not found or deprecated model errors from the Claude API? Claude 4 Opus and Sonnet 4 retire on June 15, 2026. You have 13 days to fix them. Here's every error you'll see and exactly how to resolve each one.

Error #1: "Model Not Found" (404)

This is the most common error after June 15. The API can't find the model because the name has been retired.

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

Why it happens: The model ID claude-4-opus no longer exists after June 15. The API returns a 404 because the model has been removed from Anthropic's infrastructure.

Python fix

# Before (causes error)
client.messages.create(
    model="claude-4-opus",
    messages=[{"role": "user", "content": "Hello"}]
)

# After (works)
client.messages.create(
    model="claude-opus-4-8",
    messages=[{"role": "user", "content": "Hello"}]
)

Node.js fix

// Before (causes error)
const response = await anthropic.messages.create({
    model: "claude-4-opus",
    messages: [{ role: "user", content: "Hello" }]
});

// After (works)
const response = await anthropic.messages.create({
    model: "claude-opus-4-8",
    messages: [{ role: "user", content: "Hello" }]
});

cURL fix

# Before (causes error)
curl https://api.anthropic.com/v1/messages \
  -d '{"model": "claude-4-opus", ...}'

# After (works)
curl https://api.anthropic.com/v1/messages \
  -d '{"model": "claude-opus-4-8", ...}'

Error #2: "Deprecated Model" (400)

During the deprecation window (before June 15), you may see a warning or error indicating the model is deprecated.

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "model 'claude-sonnet-4' is deprecated. Use 'claude-sonnet-4-6' instead."
  }
}

Why it happens: Anthropic may return deprecation warnings even before June 15, especially if they accelerate the retirement timeline. Some API versions surface these as errors rather than warnings.

Error #3: "Invalid Model" in SDK Response

Some SDK versions validate model names client-side before sending the request. You may get a different error depending on your SDK version.

anthropic.BadRequestError: Error code: 400 - {
  "error": {
    "type": "invalid_request_error",
    "message": "Invalid model name: claude-4-opus"
  }
}

Anthropic.InvalidRequestError: Invalid model name: claude-sonnet-4

# Update Python SDK
pip install --upgrade anthropic

# Update Node.js SDK
npm update @anthropic-ai/sdk

Error #4: "Rate Limit" or "Quota Exceeded" on New Models

If you've just migrated and suddenly hit rate limits, it's not a migration bug — it's a new rate limit bucket.

{
  "type": "error",
  "error": {
    "type": "rate_limit_error",
    "message": "Rate limit exceeded. Please retry after 60 seconds."
  }
}

Why it happens: Each model has its own rate limit. When you switch from claude-4-opus to claude-opus-4-8, you're hitting a fresh rate limit bucket. If your app sends high volume, you may exhaust the new model's limits faster than expected.

# Python — simple retry with backoff
import time

def call_with_retry(fn, max_retries=3):
    for i in range(max_retries):
        try:
            return fn()
        except anthropic.RateLimitError:
            if i == max_retries - 1:
                raise
            time.sleep(2 ** i)  # 1s, 2s, 4s

Error #5: "Authentication Failed" (401)

If you're getting 401 errors after migration, the issue isn't the model name — it's your API key or headers.

{
  "type": "error",
  "error": {
    "type": "authentication_error",
    "message": "invalid x-api-key"
  }
}

Why it happens: This is usually a coincidence with the migration — your API key may have been rotated, expired, or your environment variables aren't loading correctly. The model name change itself doesn't affect authentication.

Quick Diagnostic: Find All Deprecated Model References

Run these commands to find every reference to deprecated Claude 4 models in your codebase:

# Find all Claude 4 Opus references
grep -r "claude-4-opus" . --include="*.js" --include="*.py" --include="*.ts" \
  --include="*.json" --include="*.yaml" --include="*.yml" --include="*.env" \
  --include="*.toml" --include="*.cfg"

# Find all Claude Sonnet 4 references
grep -r "claude-sonnet-4" . --include="*.js" --include="*.py" --include="*.ts" \
  --include="*.json" --include="*.yaml" --include="*.yml" --include="*.env" \
  --include="*.toml" --include="*.cfg"

Also check these often-missed locations:

• Environment variables — .env, .env.local, .env.production
• Docker configs — docker-compose.yml, Dockerfile
• CI/CD pipelines — GitHub Actions, Vercel env vars, AWS Parameter Store
• Prompt templates — any file that hardcodes a model name in a string
• Database records — stored model preferences in your database
• Third-party libraries — check if your AI framework has cached model names

The Complete Fix: Model Name Mapping

How to Prevent These Errors (If You Haven't Migrated Yet)

You have 13 days before the deadline. Here's the fastest path:

1. Search your code — Run the grep commands above. Find every claude-4-opus and claude-sonnet-4 reference.
2. Replace model names — Use the mapping table above. One-line change per file.
3. Test — Both old and new model names work until June 15, so run parallel tests now.
4. Deploy — Push to production. No infrastructure changes needed — same API key, same SDK.

Related Resources

• Claude 4 Stopped Working? — Quick fix guide if your API calls are already failing
• Claude Deprecation Calculator — Calculate your exact migration cost and savings
• Claude 4 Migration Tool — Compare all 34 alternatives with your exact usage
• Claude 4 Deprecation Checklist — Complete 8-step migration checklist
• Claude 4 Migration Guide — Detailed code examples in Python, Node.js, and REST API
• Claude 4 Deprecation FAQ — Every question answered about the deprecation
• Claude 4 Deprecation Countdown — Live countdown and timeline
• Best Claude 4 Alternatives — Detailed comparison of all replacement options