Laguna XS 2.1 is Poolside's lightest and fastest agentic coding model, featuring a 33B total parameter Mixture-of-Experts architecture with only 3B activated parameters per token. It is purpose-built for agentic coding and long-horizon software engineering work, combining tool calling and native interleaved reasoning capabilities with a compact footprint suitable for local deployment. The model uses mixed sliding-window and global attention across 40 layers with sigmoid per-head gating and FP8 KV cache, supporting a 256K-token context window and up to 32K output tokens. Trained in-house on 15 trillion tokens, it is Poolside's first open-weight model release.