Models & pricing

Migration guide

Guide for migrating to Claude 4.6 models from previous Claude versions

Migrating to Claude 4.6

Claude Opus 4.6 is a near drop-in replacement for Claude 4.5, with a few breaking changes to be aware of. For a full list of new features, see What's new in Claude 4.6.

Update your model name

# Opus migration
model="claude-opus-4-5"     # Before
model="claude-opus-4-6"       # After

Breaking changes

Prefill removal: Prefilling assistant messages returns a 400 error on Claude 4.6 models. Use structured outputs, system prompt instructions, or output_config.format instead.
Tool parameter quoting: Claude 4.6 models may produce slightly different JSON string escaping in tool call arguments (e.g., different handling of Unicode escapes or forward slash escaping). If you parse tool call input as a raw string rather than using a JSON parser, verify your parsing logic. Standard JSON parsers (like json.loads() or JSON.parse()) handle these differences automatically.

Recommended changes

These are not required but will improve your experience:

Migrate to adaptive thinking: thinking: {type: "enabled", budget_tokens: N} is deprecated on Claude 4.6 models and will be removed in a future model release. Switch to thinking: {type: "adaptive"} and use the effort parameter to control thinking depth. See Adaptive thinking.
```
response = client.beta.messages.create(
    model="claude-opus-4-5",
    max_tokens=16000,
    thinking={
        "type": "enabled",
        "budget_tokens": 32000
    },
    betas=["interleaved-thinking-2025-05-14"],
    messages=[...]
)
```
Note that the migration also moves from client.beta.messages.create to client.messages.create — adaptive thinking and effort are GA features and do not require the beta SDK namespace or any beta headers.
Remove effort beta header: The effort parameter is now GA. Remove betas=["effort-2025-11-24"] from your requests.
Remove fine-grained tool streaming beta header: Fine-grained tool streaming is now GA. Remove betas=["fine-grained-tool-streaming-2025-05-14"] from your requests.
Remove interleaved thinking beta header: Adaptive thinking automatically enables interleaved thinking. Remove betas=["interleaved-thinking-2025-05-14"] from your requests.
Migrate to output_config.format: If using structured outputs, update output_format={...} to output_config={"format": {...}}. The old parameter remains functional but is deprecated and will be removed in a future model release.

Migrating from Claude 4.1 or earlier to Claude 4.6

If you're migrating from Opus 4.1, Sonnet 4, or earlier models directly to Claude 4.6, apply the Claude 4.6 breaking changes above plus the additional changes in this section.

# From Opus 4.1
model="claude-opus-4-1-20250805"    # Before
model="claude-opus-4-6"               # After

# From Sonnet 4
model="claude-sonnet-4-20250514"    # Before
model="claude-opus-4-6"              # After

# From Sonnet 3.7
model="claude-3-7-sonnet-20250219"  # Before
model="claude-opus-4-6"              # After

Additional breaking changes

Sampling parameters

This is a breaking change from Claude 3.x models.

Use only temperature OR top_p, not both:

# Before - This will error in Claude 4+ models
response = client.messages.create(
    model="claude-3-7-sonnet-20250219",
    temperature=0.7,
    top_p=0.9,  # Cannot use both
    ...
)

# After
response = client.messages.create(
    model="claude-opus-4-6",
    temperature=0.7,  # Use temperature OR top_p, not both
    ...
)

Tool versions

This is a breaking change from Claude 3.x models.

Update to the latest tool versions. Remove any code using the undo_edit command.
```
# Before
tools=[{"type": "text_editor_20250124", "name": "str_replace_editor"}]

# After
tools=[{"type": "text_editor_20250728", "name": "str_replace_based_edit_tool"}]
```
- Text editor: Use text_editor_20250728 and str_replace_based_edit_tool. See Text editor tool documentation for details.
- Code execution: Upgrade to code_execution_20250825. See Code execution tool documentation for migration instructions.

Handle the refusal stop reason

Update your application to handle refusal stop reasons:

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

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

Handle the model_context_window_exceeded stop reason

Claude 4.5+ models return a model_context_window_exceeded stop reason when generation stops due to hitting the context window limit, rather than the requested max_tokens limit. Update your application to handle this new stop reason:
```
response = client.messages.create(...)

if response.stop_reason == "model_context_window_exceeded":
    # Handle context window limit appropriately
    pass
```
Tool parameter handling (trailing newlines)

Claude 4.5+ models preserve trailing newlines in tool call string parameters that were previously stripped. If your tools rely on exact string matching against tool call parameters, verify your logic handles trailing newlines correctly.
Update your prompts for behavioral changes

Claude 4+ models have a more concise, direct communication style and require explicit direction. Review prompting best practices for optimization guidance.

Additional recommended changes

Remove legacy beta headers: Remove token-efficient-tools-2025-02-19 and output-128k-2025-02-19 — all Claude 4+ models have built-in token-efficient tool use and these headers have no effect.

Claude 4.6 migration checklist

Migrating to Claude Sonnet 4.5

Claude Sonnet 4.5 combines strong intelligence with fast performance, making it ideal for everyday coding, analysis, and content tasks.

For a complete overview of capabilities, see the models overview.

Sonnet 4.5 pricing is $3 per million input tokens, $15 per million output tokens. See Claude pricing for details.

Update your model name:

# From Sonnet 4
model="claude-sonnet-4-20250514"        # Before
model="claude-sonnet-4-5-20250929"      # After

# From Sonnet 3.7
model="claude-3-7-sonnet-20250219"      # Before
model="claude-sonnet-4-5-20250929"      # After

Consider enabling 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=[...]
)

Breaking changes

These breaking changes apply when migrating from Claude 3.x Sonnet models.

Sampling parameters

This is a breaking change from Claude 3.x models.

Use only temperature OR top_p, not both.
Tool versions

This is a breaking change from Claude 3.x models.

Update to the latest tool versions (text_editor_20250728, code_execution_20250825). Remove any code using the undo_edit command.
Handle the refusal stop reason

Update your application to handle refusal stop reasons.
Update your prompts for behavioral changes

Claude 4 models have a more concise, direct communication style. Review prompting best practices for optimization guidance.

Sonnet 4.5 migration checklist

Update model ID to claude-sonnet-4-5-20250929
BREAKING: Update tool versions to latest (text_editor_20250728, code_execution_20250825) — legacy versions not supported (if migrating from 3.x)
BREAKING: Remove any code using the undo_edit command (if applicable)
BREAKING: Update sampling parameters to use only temperature OR top_p, not both (if migrating from 3.x)
Handle new refusal stop reason in your application
Review and update prompts following prompting best practices
Consider enabling extended thinking for complex reasoning tasks
Test in development environment before production deployment

Migrating to Claude Haiku 4.5

Claude Haiku 4.5 is our fastest and most intelligent Haiku model with near-frontier performance, delivering premium model quality for interactive applications and high-volume processing.

For a complete overview of capabilities, see the models overview.

Haiku 4.5 pricing is $1 per million input tokens, $5 per million output tokens. See Claude pricing for details.

Update your model name:

# From Haiku 3.5
model="claude-3-5-haiku-20241022"      # Before
model="claude-haiku-4-5-20251001"      # After

Review new rate limits: Haiku 4.5 has separate rate limits from Haiku 3.5. See Rate limits documentation for details.

Consider enabling 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 prompt caching efficiency.

Explore new capabilities: See the models overview for details on context awareness, increased output capacity (64K tokens), higher intelligence, and improved speed.

Breaking changes

These breaking changes apply when migrating from Claude 3.x Haiku models.

Sampling parameters

This is a breaking change from Claude 3.x models.

Use only temperature OR top_p, not both.
Tool versions

This is a breaking change from Claude 3.x models.

Update to the latest tool versions (text_editor_20250728, code_execution_20250825). Remove any code using the undo_edit command.
Handle the refusal stop reason

Update your application to handle refusal stop reasons.
Update your prompts for behavioral changes

Claude 4 models have a more concise, direct communication style. Review prompting best practices for optimization guidance.

Haiku 4.5 migration checklist

Update model ID to claude-haiku-4-5-20251001
BREAKING: Update tool versions to latest (text_editor_20250728, code_execution_20250825) — legacy versions not supported
BREAKING: Remove any code using the undo_edit command (if applicable)
BREAKING: Update sampling parameters to use only temperature OR top_p, not both
Handle new refusal stop reason in your application
Review and adjust for new rate limits (separate from Haiku 3.5)
Review and update prompts following prompting best practices
Consider enabling extended thinking for complex reasoning tasks
Test in development environment before production deployment

Need help?

Check our API documentation for detailed specifications
Review model capabilities for performance comparisons
Review API release notes for API updates
Contact support if you encounter any issues during migration

Was this page helpful?

Models & pricing

Migration guide

Guide for migrating to Claude 4.6 models from previous Claude versions

Migrating to Claude 4.6

Claude Opus 4.6 is a near drop-in replacement for Claude 4.5, with a few breaking changes to be aware of. For a full list of new features, see What's new in Claude 4.6.

Update your model name

# Opus migration
model="claude-opus-4-5"     # Before
model="claude-opus-4-6"       # After

Breaking changes

Prefill removal: Prefilling assistant messages returns a 400 error on Claude 4.6 models. Use structured outputs, system prompt instructions, or output_config.format instead.
Tool parameter quoting: Claude 4.6 models may produce slightly different JSON string escaping in tool call arguments (e.g., different handling of Unicode escapes or forward slash escaping). If you parse tool call input as a raw string rather than using a JSON parser, verify your parsing logic. Standard JSON parsers (like json.loads() or JSON.parse()) handle these differences automatically.

Recommended changes

These are not required but will improve your experience:

Migrate to adaptive thinking: thinking: {type: "enabled", budget_tokens: N} is deprecated on Claude 4.6 models and will be removed in a future model release. Switch to thinking: {type: "adaptive"} and use the effort parameter to control thinking depth. See Adaptive thinking.
```
response = client.beta.messages.create(
    model="claude-opus-4-5",
    max_tokens=16000,
    thinking={
        "type": "enabled",
        "budget_tokens": 32000
    },
    betas=["interleaved-thinking-2025-05-14"],
    messages=[...]
)
```
Note that the migration also moves from client.beta.messages.create to client.messages.create — adaptive thinking and effort are GA features and do not require the beta SDK namespace or any beta headers.
Remove effort beta header: The effort parameter is now GA. Remove betas=["effort-2025-11-24"] from your requests.
Remove fine-grained tool streaming beta header: Fine-grained tool streaming is now GA. Remove betas=["fine-grained-tool-streaming-2025-05-14"] from your requests.
Remove interleaved thinking beta header: Adaptive thinking automatically enables interleaved thinking. Remove betas=["interleaved-thinking-2025-05-14"] from your requests.
Migrate to output_config.format: If using structured outputs, update output_format={...} to output_config={"format": {...}}. The old parameter remains functional but is deprecated and will be removed in a future model release.

Migrating from Claude 4.1 or earlier to Claude 4.6

If you're migrating from Opus 4.1, Sonnet 4, or earlier models directly to Claude 4.6, apply the Claude 4.6 breaking changes above plus the additional changes in this section.

# From Opus 4.1
model="claude-opus-4-1-20250805"    # Before
model="claude-opus-4-6"               # After

# From Sonnet 4
model="claude-sonnet-4-20250514"    # Before
model="claude-opus-4-6"              # After

# From Sonnet 3.7
model="claude-3-7-sonnet-20250219"  # Before
model="claude-opus-4-6"              # After

Additional breaking changes

Sampling parameters

This is a breaking change from Claude 3.x models.

Use only temperature OR top_p, not both:

# Before - This will error in Claude 4+ models
response = client.messages.create(
    model="claude-3-7-sonnet-20250219",
    temperature=0.7,
    top_p=0.9,  # Cannot use both
    ...
)

# After
response = client.messages.create(
    model="claude-opus-4-6",
    temperature=0.7,  # Use temperature OR top_p, not both
    ...
)

Tool versions

This is a breaking change from Claude 3.x models.

Update to the latest tool versions. Remove any code using the undo_edit command.
```
# Before
tools=[{"type": "text_editor_20250124", "name": "str_replace_editor"}]

# After
tools=[{"type": "text_editor_20250728", "name": "str_replace_based_edit_tool"}]
```
- Text editor: Use text_editor_20250728 and str_replace_based_edit_tool. See Text editor tool documentation for details.
- Code execution: Upgrade to code_execution_20250825. See Code execution tool documentation for migration instructions.

Handle the refusal stop reason

Update your application to handle refusal stop reasons:

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

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

Handle the model_context_window_exceeded stop reason

Claude 4.5+ models return a model_context_window_exceeded stop reason when generation stops due to hitting the context window limit, rather than the requested max_tokens limit. Update your application to handle this new stop reason:
```
response = client.messages.create(...)

if response.stop_reason == "model_context_window_exceeded":
    # Handle context window limit appropriately
    pass
```
Tool parameter handling (trailing newlines)

Claude 4.5+ models preserve trailing newlines in tool call string parameters that were previously stripped. If your tools rely on exact string matching against tool call parameters, verify your logic handles trailing newlines correctly.
Update your prompts for behavioral changes

Claude 4+ models have a more concise, direct communication style and require explicit direction. Review prompting best practices for optimization guidance.

Additional recommended changes

Remove legacy beta headers: Remove token-efficient-tools-2025-02-19 and output-128k-2025-02-19 — all Claude 4+ models have built-in token-efficient tool use and these headers have no effect.

Claude 4.6 migration checklist

Migrating to Claude Sonnet 4.5

Claude Sonnet 4.5 combines strong intelligence with fast performance, making it ideal for everyday coding, analysis, and content tasks.

For a complete overview of capabilities, see the models overview.

Sonnet 4.5 pricing is $3 per million input tokens, $15 per million output tokens. See Claude pricing for details.

Update your model name:

# From Sonnet 4
model="claude-sonnet-4-20250514"        # Before
model="claude-sonnet-4-5-20250929"      # After

# From Sonnet 3.7
model="claude-3-7-sonnet-20250219"      # Before
model="claude-sonnet-4-5-20250929"      # After

Consider enabling 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=[...]
)

Breaking changes

These breaking changes apply when migrating from Claude 3.x Sonnet models.

Sampling parameters

This is a breaking change from Claude 3.x models.

Use only temperature OR top_p, not both.
Tool versions

This is a breaking change from Claude 3.x models.

Update to the latest tool versions (text_editor_20250728, code_execution_20250825). Remove any code using the undo_edit command.
Handle the refusal stop reason

Update your application to handle refusal stop reasons.
Update your prompts for behavioral changes

Claude 4 models have a more concise, direct communication style. Review prompting best practices for optimization guidance.

Sonnet 4.5 migration checklist

Update model ID to claude-sonnet-4-5-20250929
BREAKING: Update tool versions to latest (text_editor_20250728, code_execution_20250825) — legacy versions not supported (if migrating from 3.x)
BREAKING: Remove any code using the undo_edit command (if applicable)
BREAKING: Update sampling parameters to use only temperature OR top_p, not both (if migrating from 3.x)
Handle new refusal stop reason in your application
Review and update prompts following prompting best practices
Consider enabling extended thinking for complex reasoning tasks
Test in development environment before production deployment

Migrating to Claude Haiku 4.5

Claude Haiku 4.5 is our fastest and most intelligent Haiku model with near-frontier performance, delivering premium model quality for interactive applications and high-volume processing.

For a complete overview of capabilities, see the models overview.

Haiku 4.5 pricing is $1 per million input tokens, $5 per million output tokens. See Claude pricing for details.

Update your model name:

# From Haiku 3.5
model="claude-3-5-haiku-20241022"      # Before
model="claude-haiku-4-5-20251001"      # After

Review new rate limits: Haiku 4.5 has separate rate limits from Haiku 3.5. See Rate limits documentation for details.

Consider enabling 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 prompt caching efficiency.

Explore new capabilities: See the models overview for details on context awareness, increased output capacity (64K tokens), higher intelligence, and improved speed.

Breaking changes

These breaking changes apply when migrating from Claude 3.x Haiku models.

Sampling parameters

This is a breaking change from Claude 3.x models.

Use only temperature OR top_p, not both.
Tool versions

This is a breaking change from Claude 3.x models.

Update to the latest tool versions (text_editor_20250728, code_execution_20250825). Remove any code using the undo_edit command.
Handle the refusal stop reason

Update your application to handle refusal stop reasons.
Update your prompts for behavioral changes

Claude 4 models have a more concise, direct communication style. Review prompting best practices for optimization guidance.

Haiku 4.5 migration checklist

Update model ID to claude-haiku-4-5-20251001
BREAKING: Update tool versions to latest (text_editor_20250728, code_execution_20250825) — legacy versions not supported
BREAKING: Remove any code using the undo_edit command (if applicable)
BREAKING: Update sampling parameters to use only temperature OR top_p, not both
Handle new refusal stop reason in your application
Review and adjust for new rate limits (separate from Haiku 3.5)
Review and update prompts following prompting best practices
Consider enabling extended thinking for complex reasoning tasks
Test in development environment before production deployment

Need help?

Check our API documentation for detailed specifications
Review model capabilities for performance comparisons
Review API release notes for API updates
Contact support if you encounter any issues during migration

Was this page helpful?