API Account-Creation Steps for the 3 Companies
Here are the API-key acquisition steps for OpenAI, Anthropic, Google. Each completes in about 5 minutes.
OpenAI API
1. Create an Account
- Go to platform.openai.com
- "Sign up" → register with Google / Microsoft / email
- Phone-number auth
2. Deposit Credit
- Settings → Billing → Add payment method
- Register a credit card
- From USD 5 minimum
3. Generate an API Key
- Left menu "API keys" → "Create new secret key"
- The key shows only once. Always copy and save it
- Name the key (multiple by use can be created)
Anthropic API
1. Create an Account
- console.anthropic.com
- Register with Google / email
- Phone-number auth
2. Deposit Credit
- Settings → Plans & Billing
- Register card, from USD 5
- New accounts may get USD 5 of credit
3. API Key
- API Keys → Create Key
- Shows only once, save
- Starts with sk-ant-
Google AI API (Gemini)
1. Start with an Existing Google Account
- Go to aistudio.google.com
- Log in with a Google account
2. Get an API Key
- "Get API key" → "Create API key"
- Free tier: ~100/day
- To go paid, create a Google Cloud project → enable Billing
Pricing Comparison (model names/rates change—check official)
| Item | OpenAI | Anthropic | |
|---|---|---|---|
| Free tier | ~USD 5 initial | Similar | 100 req/day |
| Cheapest model | GPT-5 mini class | Claude Haiku 4.5 class | Gemini Flash class |
| Top model | GPT-5.5 family | Claude Opus 4.7 | Gemini 3.1 Pro |
| Billing frequency | Monthly / credit | Credit | GCP monthly |
API Key Management Best Practices
1. Manage with Environment Variables
# .env OPENAI_API_KEY=sk-... ANTHROPIC_API_KEY=sk-ant-... GOOGLE_API_KEY=AIza...
2. Add to .gitignore
# .gitignore .env .env.local
3. Never push to GitHub
If you accidentally push, immediately invalidate the key → generate a new one → also remove commit history. AI API keys abused by attackers can cause tens of thousands of yen in damage in a day.
4. Create Keys by Use
- Split into dev, prod, test
- Minimize privilege (read-only, etc.)
- Rotate periodically
Billing Cap Settings
- OpenAI: Settings → Billing → Usage limits
- Anthropic: Settings → Limits
- Google: GCP Billing budget alerts
For personal dev, a cap of USD 20/mo; even production dev around USD 100.
Sticking Points
- Payment-method error: overseas-issued/corporate cards may be rejected, try another card
- Regional restriction: inaccessible from some regions
- SMS auth: Japanese mobile numbers OK, overseas may be rejected
Next Step
Once you get a key, go to "Environment Setup: SDK, Auth, Dev Environment."
