Anthropic and OpenAI are both telling engineers to write loops.
Not prompts.
Not agents.
Loops.
That is not a coincidence.
When the two most important AI labs on the planet independently converge on the same pattern — that is a signal worth paying attention to.
Most engineers are still thinking in terms of single calls.
Input → model → output.
The engineers winning in 2026 think in cycles.
Output becomes input. The model evaluates its own work. The loop runs until the result is right.
This is the complete breakdown of what loops are, why they matter, and how to build them ↓