With outsourcing, you hand off a project to an external team who manages delivery independently. You define the requirements and receive the finished product, but you have limited visibility into the day-to-day work.
With team augmentation, engineers join your existing team and work under your direction. They use your tools, follow your processes, and participate in your standups and code reviews. You maintain full control over priorities, architecture, and code quality.
The key difference is integration. Augmented engineers are embedded in your workflow and accountable to your engineering leadership, while outsourced teams operate separately with their own project management and delivery timelines.