Beam: Reflection's 501B open-weight model

Introducing Beam: Reflection’s 501B open-weight model October 5, 2026 8 min readWe 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 pretr...