Calling the Claude API With Streaming

Claude's API takes a list of messages and returns a reply. Streaming yields tokens as they are generated so users see output immediately.

npm install @anthropic-ai/sdk
export ANTHROPIC_API_KEY=sk-ant-...

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic();

export async function ask(prompt: string): Promise<string> {
  const res = await client.messages.create({
    model: "claude-opus-4-7",
    max_tokens: 1024,
    system: "You are a concise coding tutor.",
    messages: [{ role: "user", content: prompt }],
  });

  const block = res.content[0];
  if (block.type !== "text") throw new Error("expected text block");
  return block.text;
}

export async function askStreaming(prompt: string) {
  const stream = client.messages.stream({
    model: "claude-opus-4-7",
    max_tokens: 1024,
    messages: [{ role: "user", content: prompt }],
  });

  for await (const event of stream) {
    if (
      event.type === "content_block_delta" &&
      event.delta.type === "text_delta"
    ) {
      process.stdout.write(event.delta.text);
    }
  }

  const final = await stream.finalMessage();
  console.log("\nstop_reason:", final.stop_reason);
}

Understanding "Calling the Claude API With Streaming" in practice: AI-assisted coding shifts work from syntax recall to design thinking — models handle boilerplate so you focus on architecture. Anthropic's SDK in 20 lines. Learn messages, streaming tokens, and basic error handling — and knowing how to apply this gives you a concrete advantage.

• Apply messages API in your ai-coding workflow to get better results
• Apply streaming in your ai-coding workflow to get better results
• Apply system prompt in your ai-coding workflow to get better results
• Apply model id in your ai-coding workflow to get better results

1. 1Use AI to generate unit tests for an existing function
2. 2Ask AI to refactor a messy function and explain the changes
3. 3Have AI suggest a code review for a recent pull request

The big idea: messages.create for batch, messages.stream for UI. Narrow on block types and handle 529 like a grown-up.