When Vercel released AI SDK 6 on December 22, 2025, the headline feature was not a new model integration or a faster streaming API. It was a different kind of addition: agents became a first-class primitive in the SDK, not an afterthought patched on top of generateText . Effloow Lab installed ai@latest (currently 6.0.177 ) and inspected the package exports, constructor signatures, and available methods directly. This guide covers what actually changed, what the new ToolLoopAgent API looks like in practice, and how to move existing code from SDK 5.x to 6. Why This Matters: The Shift from Loops to Primitives In AI SDK 5.x, building an agent meant writing your own loop. You called generateText , checked for tool calls in the response, executed those tools, passed results back, and repeated until done — all in application code that you maintained yourself. The result was that every team ended up writing a slightly different, slightly buggy version of the same control loop.…