## Introducing Beam: Reflection’s 501B open-weight model October 5, 2026|8 min read Table of contents - Model Capability - Pretraining a Foundation for Reasoning - Safety and Alignment - The Path Ahead We are introducing Beam, Reflection’s first open-weight model. Beam is a sparse Mixture-of-Experts model with 501 billion total parameters, 23 billion active, built for coding, reasoning, and agentic workloads. Beam’s capabilities come from major investments in both pretraining and reinforcement learning (RL). We pretrained the model on 23.8 trillion diverse, curated, high-quality tokens from…