Migrating to Claude Haiku 4.5

Claude Haiku 4.5 is the 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.

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Migrating to Claude Haiku 4.5 from Claude Haiku 3.5 and earlier Haiku models

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.

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

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Breaking changes

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

1. Update sampling parameters

   Use only temperature OR top_p, not both. Setting both returns a 400 error on Claude Haiku 4.5.

2. Update tool versions

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

3. Handle the refusal stop reason

   Update your application to handle refusal stop reasons.

4. Update your prompts for behavioral changes

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

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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 are 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 (setting both returns a 400 error)
• 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