Critical distinction for hiring:
Data Scientists: Research-focused. Build models in notebooks. Optimize for accuracy metrics. Often PhD backgrounds. Strong in statistics and experimentation.
ML Engineers: Production-focused. Deploy models at scale. Optimize for latency, reliability, cost. Software engineering backgrounds. Strong in infrastructure and code quality.
Most failed ML projects have too many data scientists and not enough ML engineers. Proof-of-concept success requires data science skills. Production success requires ML engineering skills.
When evaluating agencies, ask: "Who deploys models to production?" If the answer is "our data scientists," that's a warning sign.