Nano Banana 2 incorporates an intermediate reasoning step that processes the prompt before the image generation pass begins. For diagram-heavy prompts—flowcharts, architecture diagrams, network topologies, data flow illustrations—this layer helps the model parse the structural intent of the prompt separately from its visual style instructions. Rather than treating "a flowchart with three decision nodes connected by arrows" as an undifferentiated stream of tokens, the reasoning step extracts the structural description, resolves spatial relationships between elements, and produces a layout plan that the generation pass then renders. The result is that node counts, connection directions, and hierarchical relationships are more likely to match the prompt specification in the final image.
The improvement is most noticeable in prompts that specify precise structural properties: a specific number of elements, a particular flow direction (top-to-bottom versus left-to-right), or explicit labeling requirements. Without the reasoning layer, these constraints compete with the model's learned priors about what diagrams typically look like, often causing the output to drift toward generic layouts rather than the specified one. With the reasoning layer active, the structural constraints are treated as hard requirements during layout planning, and the visual generation pass fills in the styling details within that constrained layout.
That said, the reasoning layer does not eliminate errors in complex diagram generation. It improves accuracy on prompts with up to roughly eight or ten structural elements; beyond that threshold, the layout planning can still produce incorrect spatial relationships or drop elements. For technical diagrams where correctness is critical—architectural documentation, engineering schematics, formal process flows—the safest approach is to generate the diagram programmatically using a dedicated diagramming library and use Nano Banana 2 for the illustrative or decorative visual elements that surround the technically precise content. The model is best treated as a visual assistant for diagram aesthetics rather than a reliable diagram compiler.