Claude API shipping

Reach for the API when…

• You're embedding Claude in a product you ship to other people.
• You want a structured response (JSON, classification, extraction).
• You want it cheap and high-volume (Batch API, prompt caching).
• You need it inside your VPC — Bedrock or Vertex.

If you just want to do a thing once, claude.ai is faster.

Five minutes, end to end.

1. Get a key at console.anthropic.com. Add a small balance ($5 is plenty to learn).
2. Save it as an env var so it never lands in code: export ANTHROPIC_API_KEY=sk-ant-… (Mac/Linux) or setx ANTHROPIC_API_KEY "sk-ant-…" (Windows).
3. Install the SDK: pip install anthropic or npm install @anthropic-ai/sdk.
4. Send a message:

import anthropic
client = anthropic.Anthropic()
msg = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello, Claude."}],
)
print(msg.content[0].text)

Three things to know.

• System prompt sets behavior and context. It's the same on every turn.
• Messages are an alternating list of user and assistant turns. Each is text, images, documents, or tool calls/results.
• Response content is a list of blocks. Plain replies have one text block. Tool-using replies may have tool_use blocks you execute and feed back.

Pick the model with model="claude-…". As of May 2026 the latest 4.x family includes Opus 4.7, Sonnet 4.6, Haiku 4.5. Default to Sonnet for cost-quality balance.

What you turn on.

Habits that pay back fast.

• Always turn on prompt caching if the same system or doc context is sent more than once. It's the biggest cost lever you have.
• Stream long responses (stream=True) so users see typing instead of waiting.
• Set max_tokens low for tool-driven loops; raise it only for the final synthesis turn.
• Capture response.usage on every call. Build a dashboard in week one, not month six.
• Test with Haiku first. If the prompt holds at Haiku, it'll fly at Sonnet.

If you live on AWS or GCP.

• Amazon Bedrock — Claude is a first-class model. Same SDK with a Bedrock client. IAM, VPC, CloudWatch.
• Google Vertex AI — same idea on GCP. Service-account auth, quotas, audit logs.
• Use these when corporate policy says data must not leave your cloud, or when you already pay one of those bills.

Related products.

Every Anthropic surface has its own page on this guide.