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# API Key Setup Guide ​

Every lab needs at least one LLM API key. If you don't have one, the mock LLM handles everything offline.

## Quick Start: Use the Mock LLM (No Key Needed) ​

All labs include automatic mock LLM fallback. Run without any setup:

bash

    python labs/L1-first-agent/solution.py test.txt "Summarize this file"

The mock client returns realistic responses. Your code runs identically with real or mock LLM.

## Provider Keys ​

### Anthropic (Claude) — Recommended ​

Best for: All course labs. Claude Sonnet is the default model used throughout.
Cost: Free credits available on signup. Labs cost ~$0.01-0.05 each with Sonnet.
Get key: console.anthropic.com
Set it:

bash

    # Windows PowerShell
    $env:ANTHROPIC_API_KEY="sk-ant-..."

    # Mac/Linux
    export ANTHROPIC_API_KEY="sk-ant-..."

### OpenAI (GPT) ​

Best for: Labs using the OpenAI SDK.
Cost: Free credits on signup. GPT-4o costs ~$0.02-0.10 per lab.
Get key: platform.openai.com/api-keys
Set it:

bash

    export OPENAI_API_KEY="sk-..."

### Google Gemini ​

Best for: Cost-sensitive experimentation. Gemini Flash is $0.15/M tokens.
Cost: Free tier available (60 requests/minute).
Get key: aistudio.google.com/apikey
Set it:

bash

    export GEMINI_API_KEY="..."

### OpenRouter (Multi-Provider) ​

Best for: Accessing multiple models from one key.
Cost: Pay-as-you-go. Free tier available for some models.
Get key: openrouter.ai/keys
Set it:

bash

    export OPENROUTER_API_KEY="sk-or-..."

## Which Key Should You Get? ​

If you... | Get
--- | ---
Want the simplest setup | None (use mock LLM)
Want to follow the course exactly | Anthropic (Claude Sonnet)
Already have OpenAI access | OpenAI (GPT-4o or o3-mini)
Want the cheapest option | Gemini (Flash is $0.15/M)
Want to try different models | OpenRouter (one key for everything)

## Testing Your Key ​

bash

    # Anthropic
    python -c "from anthropic import Anthropic; c=Anthropic(); print(c.messages.create(model='claude-sonnet-4', max_tokens=50, messages=[{'role':'user','content':'hi'}]).content)"

    # OpenAI
    python -c "from openai import OpenAI; c=OpenAI(); print(c.chat.completions.create(model='gpt-4o', messages=[{'role':'user','content':'hi'}]).choices[0].message.content)"

    # Mock (no key needed)
    python -c "from mock_llm import MockAnthropic; c=MockAnthropic(); print(c.messages.create(messages=[{'role':'user','content':'hi'}]).content[0].text)"

## Free Tier Limits ​

Provider | Free Credits | Rate Limit
--- | --- | ---
Anthropic | $5-10 signup credit | Varies by model
OpenAI | $5-18 signup credit | Varies by tier
Gemini | Free tier (60 req/min) | 60 requests/minute
OpenRouter | Varies by model | Varies

The course uses ~$0.50-2.00 in API costs total with Anthropic, or $0 with the mock LLM.