Claude Opus vs Sonnet: How to Check Your AI Model

8/10/2025

So, Are You Using Claude's Best Brain or the Speedy Sidekick? Here's How to Tell

You're working with Claude, Anthropic's impressive AI, but a nagging question keeps popping up: am I using the top-of-the-line Opus model or its faster, more affordable sibling, Sonnet? It's a valid question, especially when you're paying for a subscription or using the API for a project. The model you're using can have a BIG impact on the quality of the output, the speed of the response, & even your final bill.

Honestly, it can be a little confusing to figure out which model is active at any given moment. But don't worry, I've dug into the details & I'm here to break it all down for you. We'll cover everything from simple commands in the chat interface to checking your API calls.

First Things First: Why Does It Even Matter?

Before we get into the "how," let's talk about the "why." Understanding the difference between Opus & Sonnet is key to knowing which one you should be using for a particular task. Think of it like this: Opus is the brilliant, creative genius you go to for your most complex problems, while Sonnet is the super-smart, efficient assistant who gets things done FAST.

Claude Opus: This is the powerhouse model. It's designed for complex reasoning, in-depth analysis, & creative tasks that require a lot of nuance. If you're working on a difficult coding problem, writing a detailed report, or trying to brainstorm some truly out-of-the-box ideas, Opus is your go-to. It's more expensive to use, but the quality of its output often justifies the cost.
Claude Sonnet: Sonnet is the workhorse. It's faster than Opus & more cost-effective, making it perfect for everyday tasks. Think customer service inquiries, summarizing articles, or generating quick snippets of code. It's still incredibly capable, but it's optimized for speed & efficiency.

The latest versions, like Claude 4.1 Opus & Claude 4 Sonnet, continue this trend, with Opus pushing the boundaries of what's possible & Sonnet providing a great balance of performance & price. There's also a lighter, even faster model called Haiku, but for most users with a Pro or Team plan, the choice is between Opus & Sonnet.

For the Everyday User: Checking Your Model in "Claude Code"

If you're a "Claude Code" user with a Max subscription, you're in luck. Anthropic has made it pretty straightforward to see which model you're using. Here’s what you can do:

The
1/model
Command: This is the easiest way to check. Simply type
1/model
in the chat window, and you'll see a couple of options. It will usually show a "Default (recommended)" setting, which lets Claude choose the best model for the job based on your usage limits, & another option to explicitly select Sonnet or Opus. This is super handy because it gives you direct control over the model you're using.
Check the Input Box: Sometimes, the model name is displayed right in the chat interface. On the free tier, for example, you might see "Sonnet 3.5" in the bottom-left corner of the input box. Keep an eye out for these little clues.

It's worth noting that the "Default" setting is pretty smart. It will often start you off with Opus for your first few interactions in a session & then switch to Sonnet as you get closer to your usage limits. This is a great way to get the best of both worlds without having to think about it too much.

For the Developers: It's All in the API Call

Now, if you're a developer using the Claude API, things are a bit different. You don't have a chat interface with a handy

/model

command. Instead, the model you use is determined by what you specify in your code. This is actually a good thing because it gives you complete control over which model you're using for every single API call.

Here’s the deal: when you make a request to the Claude API, you have to include a

model

parameter in the request body. This is where you tell Anthropic which model you want to use. For example, your API call might look something like this (in Python):