API Setup Guide

Every lab in this course calls a large language model through an API. An API key is a secret string that identifies your account to the model provider and bills your usage to it. Each student issues their own key once, before the first lab.

All labs run in Google Colab through aisuite, and using the key is a copy-paste: the first cell of every lab notebook has a PASTE-YOUR-KEY-HERE placeholder — replace it with your key and run. Nothing is installed on your machine and nothing is configured outside the notebook.

1. Create your key (once)

Option A — OpenAI (course default)

1. Create an account at https://platform.openai.com/signup. This is the developer platform; a ChatGPT subscription is a separate product and does not include API credit.
2. Add prepaid credit: Settings → Billing → Add payment details, then purchase the minimum credit (currently $5). Without credit, every call fails with insufficient_quota.
3. Set a monthly usage limit of $5 (Settings → Limits), so the key can never cost more than that.
4. Create the key: API keys → Create new secret key, name it stml2026. The key (starts with sk-) is shown once — copy it into a private note; you will paste it into each lab notebook.

Option B — Anthropic

Same shape: account at https://console.anthropic.com, $5 prepaid credit under Settings → Billing, key under Settings → API keys (starts with sk-ant-). In each lab notebook, set ANTHROPIC_API_KEY instead of OPENAI_API_KEY and switch MODEL to the commented value (anthropic:claude-haiku-4-5). Everything else is identical.

2. Paste it into the lab notebook

The setup cell of every lab notebook:

import os

os.environ["OPENAI_API_KEY"] = "PASTE-YOUR-KEY-HERE"

MODEL = "openai:gpt-4o-mini"          # Anthropic accounts: "anthropic:claude-haiku-4-5"

Replace the placeholder with your key and run the cell. The key is your personal credential and your own responsibility: it sits in the notebook as plain text, so delete it from the cell before submitting or sharing the file. If a key leaks, revoke it on the provider’s API-keys page (instant and free) and create a new one — the $5 limit from step A-3 caps any damage.

Verify (do this once now)

In a fresh notebook at https://colab.research.google.com:

%pip install -q "aisuite[openai,anthropic]"
import os
os.environ["OPENAI_API_KEY"] = "PASTE-YOUR-KEY-HERE"

import aisuite
r = aisuite.Client().chat.completions.create(
    model="openai:gpt-4o-mini",
    messages=[{"role": "user", "content": "Reply with exactly: ready"}])
print(r.choices[0].message.content)

Expected output: ready. If this prints, your setup is complete and every lab in the course will run.

Expected cost

The labs use small models on short prompts; a full semester totals well under one million tokens. At current prices (gpt-4o-mini: $0.15 per million input tokens, $0.60 per million output; claude-haiku-4-5: $1 / $5), the $5 minimum credit covers the entire semester with a wide margin. There is no reason to top up more than the minimum.

Troubleshooting

Symptom	Cause	Fix
AuthenticationError / HTTP 401	Key mistyped or pasted with extra spaces	Paste again, exactly; rerun the cell
insufficient_quota / HTTP 429 (quota)	No prepaid credit on the account	Complete the billing step (A-2 or B)
RateLimitError / HTTP 429 (rate)	Too many calls per minute (new accounts have low limits)	Wait a minute and rerun
KeyError / auth error after a runtime restart	Colab reset wiped the environment	Rerun the setup cells from the top
Key shown once and lost	Providers show keys only at creation	Delete the old key, create a new one