CCAO-F Using the Claude API Practice Question
When migrating from legacy Claude models to the Claude 3.5 Sonnet Messages API, what is the most important structural change you must implement?
⚠ Common exam trap
Candidates often attempt to pass history as a single concatenated string, failing to realize that the Messages API requires a structured array of alternating role-based objects.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Adopting the structured 'messages' array format with alternating roles.
The Messages API introduced a formal separation between system instructions and conversational content. Unlike older APIs that might have relied on a flat string format, the Messages API requires a structured JSON body with defined 'user' and 'assistant' roles. This shift is essential to allow for more complex multi-turn interactions, tool use, and improved safety alignment.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Switching the API endpoint from '/v1/messages' to '/v1/completions'.
Why it's wrong here
The '/v1/completions' endpoint is the legacy API. The current and recommended way to interact with Claude 3 and 3.5 models is exclusively through the '/v1/messages' endpoint. Reverting to the old endpoint will either fail or lead to the use of an outdated, less capable model series.
- ✓
Adopting the structured 'messages' array format with alternating roles.
Why this is correct
The Messages API requires a structured list of message objects, each with 'role' and 'content' keys. This structure is fundamentally different from the legacy completion API, which took a single string. This shift allows for much better context management and is the foundation for all modern Anthropic API interactions.
- ✗
Hardcoding the temperature to 0.0 for all migrated requests.
Why it's wrong here
While setting temperature to 0.0 is useful for deterministic output, it is not a requirement of the new API. You should choose the temperature based on your specific use case, whether that is creative writing or strict data extraction. It is not a structural migration requirement for the API.
- ✗
Removing the need for a 'model' identifier in the request body.
Why it's wrong here
The 'model' field is mandatory in the Messages API request body. You must specify which version of the model you are using, such as 'claude-3-5-sonnet-20240620'. Omitting the model identifier would make the API request invalid, as the server would not know which model to invoke for the completion.
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Anthropic exam blueprint
This CCAO-F practice question is part of Courseiva's free Anthropic certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CCAO-F exam.