🎤 The interview question
"Your team wants to add an Amazon Bedrock chatbot. How would you work out what one prompt costs?"
It shows up in AIF-C01 prep and in real interviews. The strong answer: Bedrock charges per token, and every response tells you how many tokens it used. Let's prove that from the AWS CLI in 5 minutes. 👇
👉 Flow: Send one prompt → Read usage → Multiply by the price → Compare two prompts
🔧 Step 1: Set up
✅ AWS CLI v2, signed in (aws sts get-caller-identity works)
✅ Region us-east-1
✅ Model access for Amazon Nova Micro (Bedrock console → Model access)
💬 Step 2: Send one prompt with the Converse API
aws bedrock-runtime converse \ --region us-east-1 \ --model-id us.amazon.nova-micro-v1:0 \ --messages '[{"role":"user","content":[{"text":"Explain overfitting in one sentence."}]}]' \ --query '{answer: output.message.content[0].text, usage: usage}' ✅ Expected (your numbers will differ):
{ "answer": "Overfitting is when a model learns the training data so closely ...", "usage": { "inputTokens": 8, "outputTokens": 24, "totalTokens": 32 } } 👀 That usage block is your bill, in tokens.
🧮 Step 3: Turn tokens into money
Open Amazon Bedrock pricing, find Nova Micro, and copy its price per 1,000 input tokens and per 1,000 output tokens.
IN=8; OUT=24 # from usage P_IN=<price per 1K input tokens> # from the pricing page P_OUT=<price per 1K output tokens> awk -v i=$IN -v o=$OUT -v pi=$P_IN -v po=$P_OUT \ 'BEGIN { printf "USD %.8f per prompt\n", i/1000*pi + o/1000*po }' 💡 Multiply by prompts per day to get a daily cost. That's the number your manager wants.
🧨 Break it on purpose
Ask for a long answer instead:
--messages '[{"role":"user","content":[{"text":"Explain overfitting in 500 words."}]}]' 📈 outputTokens jumps, and output tokens cost more than input tokens. Then add --inference-config '{"maxTokens":50}' and watch the cost come back down.
🧹 Cost and cleanup
- 💵 A few prompts on Nova Micro cost a fraction of a cent
- 🧹 Nothing to delete: Converse calls create no resources
🎯 What you can now say in the interview (and the exam)
✅ "Bedrock on-demand pricing is per input and output token"
✅ "Every Converse response returns inputTokens and outputTokens"
✅ "Output tokens usually cost more, so I cap them with maxTokens"
✅ "Cost per prompt × prompts per day = the daily bill"
📚 Go deeper
This is the hands-on cut of Chapter 5 of our free AWS AI Practitioner (AIF-C01) course: the full chapter explains tokens, why they drive cost, and how the exam asks about them.
