Claude Sonnet 4.6 & Opus 4 API Guide: New Models Setup & Benchmarks

TL;DR

• Claude Sonnet 4.6 is Anthropic's everyday workhorse for 2026 — meaningfully better than 4.5 on complex coding tasks, same price point.
• Claude Opus 4 targets high-complexity reasoning; token cost is ~5x Sonnet, worth it only for genuinely hard tasks.
• CodeGateway setup: change base_url to https://api.codegateway.dev/v1, keep everything else identical.

Model Specs

Prices from Anthropic's official documentation (May 2026). Subject to change — check Anthropic's model page for current rates.

When accessing through CodeGateway, multiply by the applicable tier multiplier (1.2x–1.5x, declining with cumulative spend). See CodeGateway pricing tiers.

When to Use Each Model

Sonnet 4.6

• Daily coding: completions, code review, refactoring, bug triage
• Content generation: technical docs, blog posts, API documentation
• Long conversations: multi-turn debugging sessions, context-heavy chat
• Default for Claude Code: most Claude Code tasks run on Sonnet — strong price-performance ratio
• High-volume batch jobs: parallel processing of moderate-complexity requests

Opus 4

• High-complexity math and logic: algorithm design, mathematical proof verification, optimization problems
• Long-chain agent planning: multi-step orchestration where accuracy is critical
• Arbiter in sub-agent architectures: final verdict when two Workers disagree (see Sub-agents Tutorial)
• Single high-stakes outputs: when you need one shot at maximum quality

Rule of thumb: Sonnet 4.6 handles 95% of tasks adequately. Reach for Opus 4 only when Sonnet's quality is measurably insufficient and the task value justifies 5x the cost.

Setup via CodeGateway (Python)

import anthropic

# Only change: base_url points to CodeGateway. Everything else is identical to Anthropic's SDK.
client = anthropic.Anthropic(
    api_key="your-codegateway-api-key",
    base_url="https://api.codegateway.dev/v1"
)

# Sonnet 4.6 — everyday use
response = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=2048,
    messages=[{
        "role": "user",
        "content": "Review this Python function for performance issues and edge cases:\n\n[your code here]"
    }]
)
print(response.content[0].text)

# Opus 4 — high-complexity reasoning
response_opus = client.messages.create(
    model="claude-opus-4-5",
    max_tokens=4096,
    messages=[{
        "role": "user",
        "content": "Design a distributed transaction system that maintains ACID guarantees under high concurrency..."
    }]
)
print(response_opus.content[0].text)

Setup via CodeGateway (TypeScript)

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

const client = new Anthropic({
  apiKey: "your-codegateway-api-key",
  baseURL: "https://api.codegateway.dev/v1",
});

async function withSonnet(prompt: string): Promise<string> {
  const response = await client.messages.create({
    model: "claude-sonnet-4-6",
    max_tokens: 2048,
    messages: [{ role: "user", content: prompt }],
  });
  return response.content[0].type === "text" ? response.content[0].text : "";
}

// Streaming for long outputs
async function streamSonnet(prompt: string): Promise<void> {
  const stream = await client.messages.stream({
    model: "claude-sonnet-4-6",
    max_tokens: 8192,
    messages: [{ role: "user", content: prompt }],
  });

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

Migrating from Older Versions

Migration from Sonnet 4.5 (or Claude 3 series) requires only a model ID change — the API contract is identical.

Key behavioral changes to test after migration:

• Sonnet 4.6 max output is 64K (vs. 8K in 4.5). If you cap max_tokens tightly for cost control, verify the cap still applies.
• Sonnet 4.6 responds to underspecified prompts more concisely — if output quality seems lower, add more detail to your prompt rather than switching models.

Cost Benchmark: 500 Code Reviews/Day

Scenario: 500 code review requests/day, average 2,000 input tokens + 500 output tokens each.

For routine code review, Sonnet 4.6 is the right call. Opus 4's cost is 5x — reserve it for tasks that actually need it.

CodeGateway's tier multiplier drops as cumulative spend increases (1.5x → 1.2x minimum). Once monthly spend exceeds $200 equivalent, effective rates improve. See pricing tiers for the full schedule.

FAQ

Q: Is the quality difference between Sonnet 4.5 and 4.6 noticeable?

A: A: On multi-step coding tasks and complex reasoning, yes — Sonnet 4.6 is measurably better. For simple completions and text generation, the difference is minor. The main reason to migrate is the 64K output window.

Q: Does Opus 4 support Extended Thinking?

A: A: Yes, and it's currently the strong Claude model for Extended Thinking tasks. Extended Thinking works as expected through CodeGateway.

Q: What model IDs do I use with CodeGateway?

A: A: Standard Anthropic model IDs: claude-sonnet-4-6, claude-opus-4-5, claude-haiku-4-5. CodeGateway routes to the corresponding upstream models.

Q: Where do I get a CodeGateway API key?

A: A: Sign up at codegateway.dev, top up your balance, and create an API key in the dashboard. New accounts receive a $2 starter credit.

Q: Does CodeGateway support both Sonnet 4.6 and Opus 4 simultaneously?

A: A: Yes — all current Anthropic models are available, including Haiku 4.5, Sonnet 4.5, Sonnet 4.6, and Opus 4. Switch between them by changing the model ID in your requests.

Related

• Claude Code Quickstart
• Claude API Rate Limits Explained
• Claude Code Sub-agents Tutorial
• CodeGateway Pricing Tiers
• Anthropic Models Documentation