What happens if you send a Claude API request where the messages array starts with an 'assistant' role message?
Select an answer to reveal the explanation.
Short Explanation
The Claude API requires conversations to start with a user turn — assistant messages can only appear after user messages in alternating fashion.
Full Explanation
The Anthropic Messages API enforces a specific structure: the first message in the messages array must have role='user', and roles must alternate (user, assistant, user, assistant...). Attempting to start with an assistant message results in a 400 validation error. This mirrors natural conversation flow where a user initiates and Claude responds. Option A is wrong — roles are not interchangeable. Option C is wrong — the API doesn't auto-insert messages. Option D is wrong — the API returns an error, it doesn't silently skip messages.