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StaticBatchingUtility.Combine
to batch meshes at runtime.Static Batching in Unity creates a Read-Only mesh named “Combined Mesh (root: <root-game-object>)”, with a Submesh for each batched renderer. Unity invokes a separate draw call for each range of indices within the combined mesh buffer.
Note that this means Unity does not actually render the entire batch in a single draw call. As they mention, truly merging all meshes would make culling vastly less effective.
Instead, the performance comes from issuing fewer material / mesh change state operations (in OpenGL at least). In a lot of ways, this ends up being more similar to SRP Dynamic Batching.