Reflection AI unveils Beam, its 501B open-weight model

Reflection AI unveiled Beam on October 5, 2026, its first open model. The system has 501 billion parameters in total but only uses 23 billion at a time, using a sparse Mixture-of-Experts design — meaning specialists switch on as needed, Reflection AI says. It targets coding, reasoning and agentic tasks. Open weights let users inspect and fine-tune it.