GPT-OSS-20B is an open-weight language model built on a Mixture-of-Experts architecture that activates only a fraction of its weights per token. According to an independent deployment-focused study, the model carries roughly 20.9B total parameters but engages only about 3.61B of them at inference, leaving the active parameter share at around 17.3 percent. This sparse-activation design is the core of its identity and informs both its efficiency profile and the routing-related overhead observed during prefill.
An independent single-GPU benchmark on an NVIDIA H100 in bf16 precision found that GPT-OSS-20B delivers higher decode throughput and more tokens per Joule than similarly sized dense models like Qwen3-32B and Yi-34B, while using substantially less peak VRAM and less energy per 1,000 generated tokens. The trade-off is a longer time-to-first-token because MoE routing adds prefill cost, and decode throughput gradually declines as context grows, dropping about 40 percent at 4K tokens compared with the 512-token baseline. Per active billion parameters, the model shows roughly an order-of-magnitude advantage in throughput and energy efficiency over the dense baselines, making it well suited to single-GPU production serving where memory and power budgets matter more than raw accuracy.