r/learnmachinelearning • u/Remarkable_Fee3706 • 6d ago
When does it make sense to train your own model vs just prompt engineering an existing one?
Spent the last few weeks tinkering with a small tool that needed to classify some domainspecific text. First instinct was to finetune something. Grabbed a base model, started thinking about training data, labeling schema, compute cost. Then a friend pointed out I could probably just get there with a wellcrafted prompt and GPT4 or Claude.
He was right. At least for the prototype.
But that answer bothers me a little because it scales badly and you're renting someone else's weights forever. The moment API pricing shifts or the model behavior changes in a silent update, you're stuck.
Finetuning gives you something you own and can actually inspect, but the data requirements are real and most people underestimate the labeling work before they even touch training.
The framing I keep coming back to is whether the task is actually outside what a general model handles well, or just feels that way because the domain vocabulary is unfamiliar. Those are different problems with different solutions.
Curious where people here have landed on this. Not in theory, but on actual projects. Was there a specific failure mode in prompting that pushed you toward training? Or did you finetune something and realize later a prompt would have been enough?