What is a model family?
A model family is a group of language models that share a base architecture but differ in size, capability, and price. Claude is a family: Claude 3 Haiku (small, cheap), Claude 3 Sonnet (medium), Claude 3 Opus (large, expensive). GPT-4 is a family: GPT-4, GPT-4 Turbo, GPT-4o, GPT-4o mini.
The concept emerged as providers realised that one model size does not fit all tasks. A simple classification task does not need the same model as a complex legal analysis. Offering a family lets developers match cost to complexity.
Why it matters
Model family awareness is cost engineering. Using Opus for a task that Haiku can handle wastes 60x the cost. sourc.dev tracks model families as an attribute so you can compare within and across families — finding the cheapest model that meets your quality threshold.