errors changedapi/errors
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5858The API always returns errors as JSON, with a top-level `error` object that always includes a `type` and `message` value. The response also includes a `request_id` field for easier tracking and debugging. For example:
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60```json JSON
60```text JSON wrap
6161{
6262 "type": "error",
6363 "error": {
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422422 ```
423423</CodeGroup>
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425See [Streaming messages](https://platform.claude.com/docs/en/build-with-claude/streaming#get-the-final-message-without-handling-events) for more details.
425See [Get the final message without handling events](https://platform.claude.com/docs/en/build-with-claude/streaming#get-the-final-message-without-handling-events) for more details.
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427427## Common validation errors
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431431Claude 4.6 and later models and [Claude Mythos Preview](https://anthropic.com/glasswing) do not support prefilling assistant messages. Sending a request with a prefilled last assistant message to any of these models returns a 400 `invalid_request_error`:
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433```json
433```text
434434{
435435 "type": "error",
436436 "error": {
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