The concept
Claude.ai is the chat app. The Claude API is the same models called from your own code, so the work runs inside your systems.
Three pieces:
- API key: your password for the API, created in the Claude Console (platform.claude.com). It's shown once, so store it safely (Day 51).
- SDK: Anthropic's Python library, installed with pip install anthropic.
- Messages API: you send a model name, a max_tokens limit (the reply's length cap, in tokens) and a list of messages; you get the reply back.
Walkthrough: support call → 3 action points
The transcript (illustrative): a customer's broadband has dropped every evening for a week. The agent promised a callback, an engineer visit and a bill credit.
1. Save it as call.txt.
2. Set your key: export ANTHROPIC_API_KEY="..." (the SDK reads it automatically).
3. Save this as summarize.py:
import anthropic
client = anthropic.Anthropic()
call = open("call.txt").read()
msg = client.messages.create(
model="claude-opus-5-5",
max_tokens=500,
messages=[{"role": "user", "content": "Summarize this support call as exactly 3 action points, each with an owner:\n\n" + call}])
print(msg.content[0].text)
4. Run python summarize.py. You get something like:
- Agent: call the customer back by Friday.
- Field team: book an engineer visit.
- Billing: apply the promised credit.
The reply's content is a list of blocks; here the first is text. It also reports token usage, which is what you pay for.
The model ID above is the one in Anthropic's quickstart today. IDs change; pick a current one at https://platform.claude.com/docs/en/about-claude/models/overview
Where you see it at work
- Customer experience: every call gets the same summary format for the CRM.
- Banking: complaint calls summarized for the case file, reviewed by a person.
- Insurance: first-notice-of-loss calls turned into a claims checklist.
- Healthcare: admin calls summarized for the front desk.
- Business analysis: interview notes into decisions and open questions.
Try it today (10–15 min)
1. Create a key: https://platform.claude.com/docs/en/get-api-key
2. Follow the Python quickstart: https://platform.claude.com/docs/en/get-started
3. Swap in the code above with a made-up transcript. Never real customer data.
4. Change "3 action points" to "a JSON list with task and owner" and compare.
In one sentence
A Claude API call is a model, a length limit and your messages, sent with a secret key, turning raw text into next steps from your own code.
What text at your work would you summarize first? 👇