So, you're trying to use Anthropic's top-tier Claude Opus model, but for some reason, your outputs feel... less Opus & more Sonnet. It’s a super frustrating situation, especially when you’re paying for the premium model & relying on its advanced reasoning for complex tasks.

Turns out, you're not going crazy. There are a few reasons this might be happening, ranging from a simple typo in your code to more nuanced platform behaviors. Let's break it all down so you can make sure you're ACTUALLY using Opus when you mean to.

Here’s the thing, I’ve been digging into this, & it seems to be a pretty common headache. I’ve seen developers on Reddit & GitHub forums pulling their hair out over this exact issue. So, let's get to the bottom of it.

Honestly, most of the time, the issue is just using the wrong model name in your API call. It's an easy mistake to make. You might be using a shorthand name, an old name, or just a slight variation that the API doesn't recognize, causing it to default to a different model, often Sonnet.

Anthropic has a very specific set of model IDs. If you want Opus, you need to be explicit.

Here are the official model names you should be using, straight from the source. I'd recommend using the full version with the date to guarantee you're locked into a specific, stable version.

For convenience, they also offer aliases like , but the official advice is to use the full, dated model ID in production to ensure consistent behavior. This is because aliases can be updated to point to new model snapshots over time, which could introduce unexpected changes.

Let's look at what this looks like in practice. Here’s a basic Python example using Anthropic's official library. Pay close attention to the parameter.