I've been testing the new GPT 5.6 models for the past few days, and one question keeps coming up.
Which one should I actually use?
The lineup includes Sol, Terra, and Luna. On paper they all look good, but after trying them on real coding tasks, they feel very different.
Here's what I think after using all three.
Sol
If you only care about getting the best result possible, Sol is the one to use.
Almost every time I tested it, the code was cleaner, the reasoning was better, and it made fewer mistakes than the other two models. It also spends more time thinking, so don't expect instant responses.
The downside is the price.
It costs around $5 per million input tokens and $30 per million output tokens. If you're using it a lot, the cost adds up pretty quickly.
I would use Sol for things like:
- Complex projects
- Refactoring large codebases
- Fixing difficult bugs
- Anything where quality matters more than speed
Terra
Terra is probably my favorite out of the three.
It gives really good results while being much faster than Sol, and it's also a lot cheaper. During my testing, it handled most coding tasks without any issues.
It might not be as accurate as Sol every single time, but honestly, for everyday coding, I don't think most people will notice.
Pricing is around:
- $2.50 per million input tokens
- $15 per million output tokens
If you're coding every day, Terra is probably the model you'll end up using the most.
Luna
Luna was the only model that disappointed me a bit.
It's slower than I expected, and the quality wasn't very consistent. Sometimes it solved a task just fine, and other times it struggled with things that Terra finished easily.
The good thing is the price.
It costs about:
- $1 per million input tokens
- $6 per million output tokens
If you're on a tight budget or just trying simple prompts, Luna is still worth considering. Just don't expect the same quality as Sol or Terra.
Which One Would I Pick?
After using all three, this is how I'd choose.
Use Sol if:
- You want the highest quality.
- You're working on something important.
- You don't mind paying more.
Use Terra if:
- You want the best balance between quality, speed, and price.
- You need a model for everyday coding.
Use Luna if:
- Keeping costs low matters the most.
- Your tasks are simple.
- You're okay spending some extra time fixing the output.
One More Thing
Your prompt still matters.
A better prompt usually gives a better result, no matter which model you're using. Even Luna performs better with clear instructions, although I still don't think it can match Sol or Terra.
Final Thoughts
If someone asked me to recommend just one model, I'd probably say Terra. It feels like the sweet spot for most developers.
If quality is your top priority, go with Sol.
If you're trying to spend as little as possible, Luna gets the job done, but don't expect miracles.
Those are just my thoughts after testing all three. Your experience might be different depending on what you're building, but hopefully this gives you a better idea of which model is worth using.
The video: GPT 5.6 Sol vs Terra vs Luna
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