prompting-claude-haiku-5-5 changedbuild-with-claude/prompt-engineering/prompting-claude-haiku-5-5
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2121<Note>
2222 For the breaking API changes when migrating from Claude Haiku 4.5, see the [migration guide](https://platform.claude.com/docs/en/models/haiku-5-5/migration-guide).
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24 Several sections on this page suggest text to add to your system prompt. Add it to new conversations only. A request that sends thinking blocks back after `system` changed can return a 400 error, so a stored conversation resumed with the new system prompt can fail. To change instructions partway through a conversation, [put them in the newest turn](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#changing-context). On the Claude API, Amazon Bedrock, and Claude Models on Google Cloud (Google managed), you can instead [append a system message to the conversation](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#new-instructions).
24 Several sections on this page suggest text to add to your system prompt. Add it to new conversations only. A request that sends thinking blocks back after `system` changed can return a 400 error, so a stored conversation resumed with the new system prompt can fail. To change instructions partway through a conversation, [put them in the newest turn](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#changing-context). On the Claude API, Amazon Bedrock, Claude Platform on AWS, Claude Models on Google Cloud (Anthropic managed), and Claude Models on Google Cloud (Google managed), you can instead [append a system message to the conversation](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#new-instructions).
2525</Note>
2626
2727## Use effort to control thinking
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