v2 is a namespace containing a new version of the compiler (still in development).
v2.ast is the default index-based AST graph used by the v2 builder for
parsing, type checking, markused, and native SSA input:
ast.flatten_files(files) builds ast.FlatAst with contiguous nodes and edges.ast.legacy_ast_stats(files) estimates memory/shape metrics for recursive AST files.flat.stats() and flat.count_reachable_nodes() report flat graph size and reachability.flat.to_files() remains available for focused flat-reader roundtrip tests.