Scale AI is the 'gold standard' for data labeling, effectively functioning as the utility company for the AI industry. If you are OpenAI or the DoD, this is your vendor; they practically invented modern RLHF workflows and have an army of human labelers that no software-only tool can match. However, for 95% of developers, it is overkill—pricing is opaque (expect $50k+ contracts), and the self-serve tier feels like an afterthought. Use it if you need massive scale or specialized 3D/LLM data; avoid it if you just need to label 500 images for a side project.