Claude Opus: what the senior model is for and when it pays off

Claude Opus is the senior line of Claude models. The question "what is Claude Opus for" usually comes up when two lines of a price list sit side by side, Opus and Sonnet, and the first one costs more. Below we cover what Opus 5.5 is, which tasks use it and how to calculate whether the difference pays off in your scenario. A caveat up front: we do not claim that Opus "writes better" or is "smarter". We give prices, context, the strength index and a method for testing on your own tasks.

What Claude Opus is and where it sits in the line

Several Claude models are available in Zukko on October 18, 2026. Main numbers from the catalog, prices per 1M tokens:

The strength index is the Intelligence Index from Artificial Analysis; we give no other quality metrics. The table shows that claude-opus-5-5 has the highest index in the catalog, and its price is exactly double Sonnet 5.5 (0.8 versus 0.4 for input, 4 versus 2 for output). Anthropic's official prices for comparison: Opus 5.5 is 4 / 20, Sonnet 5.5 is 2 / 10. The current list and prices: GET https://api.zukko.pro/v1/models. A review of the model itself: Claude Opus 5.5: calling it via API and testing↗.

What Opus is for: typical scenarios

The senior model is usually tried where the cost of an error or an extra iteration is high. These are hypotheses to test, not promises:

1. Hard code. Refactoring across several modules, hunting an intermittent bug, migrations with cross-file dependencies. One wrong edit costs hours of debugging.
2. Long agent sessions. An agent (Claude Code, opencode, Cline) takes dozens of steps in a row, and a mistake at an early step carries forward. Fewer backtracks means a cheaper session overall.
3. Analysis of large documents. A 1M token context lets you load a contract, a report or a whole codebase. But Sonnet has the same window size, so the window alone is no reason to take Opus.
4. Planning and parsing ambiguous requirements. Draft a plan for a smaller model that then executes the steps.
5. Working with images. Both lines accept image input, so this is not a difference.

Where the task is simple (classification, field extraction, short answers, translation), the senior model is often excessive: for bulk jobs start with cheap models such as deepseek-v4.1-flash or glm-5.3-flash and check whether they are enough.

When Opus pays off: the formula

Opus costs twice as much per token. So it pays off if on your task it delivers a result at least twice as reliable, that is, needs half the attempts. Written down:

cost of a solution = cost of one attempt × average number of attempts
Opus is cheaper if: attempts_Sonnet / attempts_Opus > 2

If Sonnet solves the task on the first try, the extra spend is not needed. If it needs 3 attempts on average and Opus manages in 1.3, then 3 / 1.3 ≈ 2.3, so Opus is cheaper, and you also save your own time. Real attempt counts come only from your tasks: take 10 to 20 typical ones, run both models and count. A comparison practice: Sonnet 5 or Opus 5.5↗.

A calculation on one scenario

Scenario: an agent session in Claude Code, 20 requests, 1.2M input tokens and 40,000 output tokens in total. Assumptions are stated explicitly.

Option 1: no cache (for example, when connected via the OpenAI format).

• Opus 5.5: input 1.2 × 0.8 = $0.96; output 0.04 × 4 = $0.16; total $1.12.
• Sonnet 5.5: input 1.2 × 0.4 = $0.48; output 0.04 × 2 = $0.08; total $0.56.

Option 2: with cache in the Anthropic format (/v1/messages, Claude Code). Suppose of the 1.2M input, 100,000 is written to cache, 1,000,000 is read from cache and 100,000 tokens are fresh.

• Opus 5.5: write 0.1 × 1 = $0.10; read 1.0 × 0.08 = $0.08; fresh input 0.1 × 0.8 = $0.08; output 0.04 × 4 = $0.16; total $0.42.
• Sonnet 5.5: write 0.1 × 0.5 = $0.05; read 1.0 × 0.05 = $0.05; fresh input 0.1 × 0.4 = $0.04; output 0.04 × 2 = $0.08; total $0.22.

For comparison, at official prices the same volume without cache would cost: Opus 1.2 × 4 + 0.04 × 20 = $4.80 + $0.80 = $5.60; Sonnet 1.2 × 2 + 0.04 × 10 = $2.40 + $0.40 = $2.80. The dollar gap between models is small on one session, but over hundreds of sessions a month it adds up. The cache share depends on the tool and agent behavior, so take real numbers from the "Usage" section of the dashboard. How cache is billed: prompt caching: read and write↗.

How to test on your own tasks

A minimal half-hour plan:

1. Pick 10 typical tasks from your work.
2. Run each on claude-sonnet-5-5, then on claude-opus-5-5 with the same instruction.
3. Judge the result with tests, review or a checklist, not by impression.
4. Record the attempt count and total spend per model.
5. Apply the formula above.

A simple way to switch between models in code:

import os
from openai import OpenAI

client = OpenAI(base_url="https://api.zukko.pro/v1", api_key=os.environ["ZUKKO_API_KEY"])

def ask(model: str, prompt: str):
    r = client.chat.completions.create(
        model=model,
        messages=[{"role": "user", "content": prompt}],
        max_tokens=1500,
    )
    return r.choices[0].message.content, r.usage

for m in ("claude-sonnet-5-5", "claude-opus-5-5"):
    text, usage = ask(m, "Find the bug in this function and suggest a fix: ...")
    print(m, usage.prompt_tokens, usage.completion_tokens)

In the OpenAI format Claude is billed without a cache discount; for long sessions use the Anthropic format. Another option is a cascade: a smaller model first, with claude-opus-5-5 brought in only on escalation, when the smaller one fails.

FAQ

Is Opus always better than Sonnet?

We do not claim that. Opus 5.5 has a higher strength index (58 versus 48), but on a particular task the result may be the same. Test on your own data.

How does Opus 5.5 differ from Opus 5?

In the catalog they have the same input and output price ($0.8 / $4); 5.5 has a higher strength index (58 versus 50). The choice works the same way: run your own tasks.

When should I not take Opus?

For bulk classification, short answers, field extraction and translation of large volumes: smaller, cheaper models usually suffice there, and the price difference multiplies by the number of requests.

How do I start?

Create a key in the dashboard, set a daily limit and connect claude-opus-5-5 using the model list↗.