Deep Research (DR) systems iteratively plan, retrieve evidence, and synthesize long-form reports in response to complex, open-ended queries. Existing approaches suffer from context overload, role entanglement, and error propagation over long horizons, while the most capable DR systems remain locked behind massive proprietary models. We present DeepDiver-DR (DD-DR), a multi-agent framework that decomposes the DR process into three specialized roles—planner, information seeker, and writer—coordinated through a persistent, file-based shared workspace. Each role is further equipped with fine-grained, DR-specific tools. To support rigorous evaluation, we introduce RubricWrite-Bench (RW-Bench), a benchmark of 100 rubric-based writing queries with a two-phase assessment of global report quality and point-level rubric fulfillment. Experiments show that DD-DR (30B) establishes a new state of the art among models at the same parameter scale on the DeepResearch Bench, and achieves performance competitive with leading proprietary DR systems on RW-Bench. Ablations further confirm the contribution of the architectural components.