Why My o3-mini Model Call Was Failing and How I Fixed It with High Reasoning in Cursor

I was building something cool with Cursor’s o3-mini model when my code suddenly started failing. Every time I tried boosting its reasoning power by setting ‘reasoning_effort’ to ‘high’, I’d get cryptic errors that stopped me cold. What felt like a showstopper turned out to have a surprisingly simple fix – once I cracked the pattern.

What Kept Breaking My Code

Like many developers, I wanted maximum brainpower from o3-mini for complex tasks. The OpenAI docs mentioned setting reasoning effort, so I added it to my API calls in Cursor:

const completion = await openai.chat.completions.create({
model: "o3-mini",
reasoning_effort: "high", // This caused all the trouble
messages: [
{
role: "user",
content: prompt
}
],
store: true
});

Instead of smarter responses, I got errors like ‘model_not_found’ or claims my plan didn’t support ‘o3-mini-high’. Super frustrating when you’re mid-flow! I must’ve burned an hour searching forums before the lightbulb moment.

My “Oh!” Moment

Turns out Cursor handles o3-mini differently than raw OpenAI API. That ‘high reasoning’ mode I desperately wanted? It’s actually the default behavior in Cursor. By adding the parameter, I was accidentally telling it to look for a non-existent ‘o3-mini-high’ variant. No wonder it choked!

The Simple Fix That Worked

Getting o3-mini humming with full reasoning power took just two changes:

• Call it by its base name only: Use plain ‘o3-mini’ without any suffixes
• Drop the reasoning_effort parameter completely: Cursor handles this automatically
• Clean code example: Here’s what finally worked for me:const completion = await openai.chat.completions.create({
model: "o3-mini", // Just the model name
messages: [
{
role: "user",
content: prompt
}
],
store: true
});

Deleted one line, errors vanished. Felt almost too easy after the headache!

Why This Matters For Your Work

Here’s what I wish I’d known earlier: Cursor’s o3-mini comes pre-tuned for heavy reasoning tasks. That ‘-high’ suffix? Totally unnecessary in this environment. If you’re testing models like DeepSeek-R1 against o3-mini, remember you’re already getting peak performance out of the box. Check Cursor’s docs occasionally for updates, but right now – simpler code works better. This little tweak got me back to building in minutes.