Migrating to Claude 4.5

Update sampling parameters

This is a breaking change from the Claude Sonnet 3.7.

Use only temperature OR top_p, not both:

# Before (Claude Sonnet 3.7) - This will error in Sonnet 4.5
response = client.messages.create(
    model="claude-3-7-sonnet-20250219",
    temperature=0.7,
    top_p=0.9,  # Cannot use both
    ...
)

# After (Claude Sonnet 4.5)
response = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    temperature=0.7,  # Use temperature OR top_p, not both
    ...
)

Handle the new refusal stop reason

Update your application to handle refusal stop reasons:

response = client.messages.create(...)

if response.stop_reason == "refusal":
    # Handle refusal appropriately
    pass

Update text editor tool (if applicable)

This is a breaking change from the Claude Sonnet 3.7.

Update to text_editor_20250728 (type) and str_replace_based_edit_tool (name). Remove any code using the undo_edit command.

# Before (Claude Sonnet 3.7)
tools=[{"type": "text_editor_20250124", "name": "str_replace_editor"}]

# After (Claude Sonnet 4.5)
tools=[{"type": "text_editor_20250728", "name": "str_replace_based_edit_tool"}]

See Text editor tool documentation for details.

Remove token-efficient tool use beta header

Token-efficient tool use is a beta feature that only works with Claude 3.7 Sonnet. All Claude 4 models have built-in token-efficient tool use, so you should no longer include the beta header.

Remove the token-efficient-tools-2025-02-19 beta header from your requests:

# Before (Claude Sonnet 3.7)
client.messages.create(
    model="claude-3-7-sonnet-20250219",
    betas=["token-efficient-tools-2025-02-19"],  # Remove this
    ...
)

# After (Claude Sonnet 4.5)
client.messages.create(
    model="claude-sonnet-4-5-20250929",
    # No token-efficient-tools beta header
    ...
)

Remove extended output beta header

The output-128k-2025-02-19 beta header for extended output is only available in Claude Sonnet 3.7.

Remove this header from your requests:

# Before (Claude Sonnet 3.7)
client.messages.create(
    model="claude-3-7-sonnet-20250219",
    betas=["output-128k-2025-02-19"],  # Remove this
    ...
)

# After (Claude Sonnet 4.5)
client.messages.create(
    model="claude-sonnet-4-5-20250929",
    # No output-128k beta header
    ...
)

Consider enabling extended thinking for complex tasks

Enable extended thinking for significant performance improvements on coding and reasoning tasks (disabled by default):

response = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=16000,
    thinking={"type": "enabled", "budget_tokens": 10000},
    messages=[...]
)

Extended thinking impacts prompt caching efficiency.

Update your model name:

# Before (Haiku 3.5)
model="claude-3-5-haiku-20241022"

# After (Haiku 4.5)
model="claude-haiku-4-5-20251001"

Update tool versions (if applicable)

This is a breaking change from the Claude Haiku 3.5.

Haiku 4.5 only supports the latest tool versions:
```
# Before (Haiku 3.5)
tools=[{"type": "text_editor_20250124", "name": "str_replace_editor"}]

# After (Haiku 4.5)
tools=[{"type": "text_editor_20250728", "name": "str_replace_based_edit_tool"}]
```
- Text editor: Use text_editor_20250728 and str_replace_based_edit_tool
- Code execution: Use code_execution_20250825
- Remove any code using the undo_edit command

Update sampling parameters

This is a breaking change from the Claude Haiku 3.5.

Use only temperature OR top_p, not both:

# Before (Haiku 3.5) - This will error in Haiku 4.5
response = client.messages.create(
    model="claude-3-5-haiku-20241022",
    temperature=0.7,
    top_p=0.9,  # Cannot use both
    ...
)

# After (Haiku 4.5)
response = client.messages.create(
    model="claude-haiku-4-5-20251001",
    temperature=0.7,  # Use temperature OR top_p, not both
    ...
)

Review new rate limits

Haiku 4.5 has separate rate limits from Haiku 3.5. See Rate limits documentation for details.
Handle the new refusal stop reason

Update your application to handle refusal stop reasons.
Consider enabling extended thinking for complex tasks

Enable extended thinking for significant performance improvements on coding and reasoning tasks (disabled by default):
```
response = client.messages.create(
    model="claude-haiku-4-5-20251001",
    max_tokens=16000,
    thinking={"type": "enabled", "budget_tokens": 5000},
    messages=[...]
)
```
Extended thinking impacts efficiency.
Explore new capabilities

See What's new in Claude 4.5 for details on context awareness, increased output capacity (64K tokens), higher intelligence, and improved speed.
Test your implementation

Test in a development environment before deploying to production to ensure all breaking changes are properly handled.

Migrating to Claude 4.5

Migrating from Claude Sonnet 3.7 to Claude Sonnet 4.5

Migration steps

Migrating to Claude 4.5

Migrating from Claude Sonnet 3.7 to Claude Sonnet 4.5

Migration steps

Sonnet 3.7 → 4.5 migration checklist

Features removed from Claude Sonnet 3.7

Migrating from Claude Haiku 3.5 to Claude Haiku 4.5

Migration steps

Haiku 3.5 → 4.5 migration checklist

Choosing between Sonnet 4.5 and Haiku 4.5

Choose Claude Sonnet 4.5 (most intelligent) for:

Choose Claude Haiku 4.5 (fastest and most intelligent Haiku) for:

Extended thinking recommendations

Other migration scenarios

Migrating from Claude Sonnet 4 → Sonnet 4.5

Migrating from Claude Opus 4.1 → Sonnet 4.5

Migrating from Claude Opus 4.1 → Opus 4.5

Migrating between Claude 4.5 models

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