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This guide covers migrating Messages API code. If you use Claude Managed Agents, no changes beyond updating the model name are required.

Automate your migration with the Claude API skill. In Claude Code, run /claude-api migrate to invoke the bundled Claude API skill. It works for any current Claude model as the target:

/claude-api migrate this project to claude-haiku-4-5

The skill applies the model ID swap and, as needed, breaking parameter changes, prefill replacement, and effort calibration for your target model across your code base, then produces a checklist of items to verify manually. It asks you to confirm the migration scope (entire working directory, a subdirectory, or a specific file list) before editing any files. The skill also detects Amazon Bedrock and Claude Platform on AWS clients and adjusts model ID formats and feature changes for those platforms.

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.

For Claude Haiku 4.5 pricing, see Claude pricing.

For significant performance improvements on coding and reasoning tasks, consider enabling extended thinking with thinking: \{type: "enabled", budget_tokens: N\}.

Extended thinking impacts prompt caching efficiency.

Extended thinking is deprecated in Claude 4.6 models and removed in Claude Opus 4.7. If using newer models, use adaptive thinking instead.

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.

Breaking changes

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

1. Update sampling parameters

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

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

2. Update tool versions

   This is a breaking change when migrating 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.

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.

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