CCAO-F Using the Claude API Practice Question
A team is instrumenting its Claude Messages API integration to monitor usage and cost. Which TWO response fields should the developer log to track token consumption per request? (Choose two.)
⚠ Common exam trap
The trap here is logging descriptive response fields such as the model name or message id and assuming they convey token usage when only the usage object reports counts.
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
✓
usage.output_tokens
The usage object in a Messages API response exposes input_tokens and output_tokens, which together quantify consumption for each call. Because input and output tokens are priced separately, both must be logged for accurate cost attribution. Other fields like stop_reason, id, and model provide context or tracing value but do not measure token usage.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
stop_reason
Why it's wrong here
stop_reason explains why generation ended, such as reaching an end turn or hitting max_tokens. While useful for debugging truncation, it does not quantify token consumption. Logging it does not help attribute cost per request, so it is not a token-count field and does not satisfy the monitoring goal.
- ✗
model
Why it's wrong here
The model field echoes which model produced the response, which matters for pricing tiers and auditing. However, it states identity, not quantity. Tracking model names helps map requests to rate cards but does not report how many tokens were consumed, so it cannot fulfill a per-request consumption metric on its own.
- ✓
usage.output_tokens
Why this is correct
The usage object also reports output_tokens, the tokens generated in the completion. Because output tokens are typically priced differently from input tokens, logging this separately is necessary for precise cost accounting. Combined with input tokens, it gives a complete per-request consumption picture from the API itself.
- ✗
id
Why it's wrong here
The id field is a unique identifier for the message response, valuable for tracing and support escalation. It carries no token or billing information, so logging it alone cannot reveal consumption. It complements usage data for correlation but is not itself a measure of tokens used in the request.
- ✓
usage.input_tokens
Why this is correct
The usage object reports input_tokens, the number of tokens consumed by the prompt. Logging this value lets the team attribute prompt-side cost and monitor how prompt size changes over time. It is a direct, authoritative measure from the API response rather than an estimate, making it essential for accurate consumption tracking.
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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
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