# OpenAI gpt-oss 20B (MoE) VRAM Requirements & Hardware Sizing Guide

> **Quick Summary (Answer Capsule)**: Running OpenAI gpt-oss 20B (MoE) requires 14.43 GB at Q4_K_M (4-bit), 24.96 GB at Q8_0 (8-bit), and 44.73 GB at FP16. Recommended hardware sweet spot: NVIDIA GeForce RTX 5060 Ti 16GB. Scaling context past 32k tokens requires enabling FP8 KV-cache (-ctk q8_0) to prevent CUDA allocation failures.

## Memory Specifications by Precision
| Quantization Format | Precision Level | Required VRAM (8k context) | Quality Retention | Minimum Recommended GPU |
|---|---|---|---|---|
| 4-Bit (Q4_K_M) | Recommended Default | 14.43 GB | >98.2% Perplexity | NVIDIA GeForce RTX 5060 Ti 16GB |
| 8-Bit (Q8_0) | Near Lossless | 24.96 GB | ~99.9% Perplexity | Workstation / High-Tier GPU |
| 16-Bit (FP16/BF16) | Uncompressed Full | 44.73 GB | 100% Fidelity | Multi-GPU / Datacenter |

## Architectural Memory Analysis
OpenAI's gpt-oss 20B is an open-weights Mixture-of-Experts reasoning model containing 20.9B total parameters while activating just 3.6B parameters per token across 32 layers. Using alternating sliding window attention and native MXFP4 quantization, its 4-bit weight footprint consumes 12.8 GB, fitting comfortably within 16GB graphics cards for rapid local inference.

## Tier 1 Free Software Optimization ($0)
In llama.cpp and vLLM, launch with native `--quantization mxfp4` kernels and pass `-fa on`. MXFP4 maintains near-lossless reasoning fidelity while cutting memory bandwidth overhead, streaming tokens at 85+ tok/s.

## 1-Click Launch Terminal Snippets
- Ollama: `ollama run gpt-oss-20b:q4_K_M`
- vLLM: `vllm serve OpenAI/gpt-oss-20b --max-model-len 8192 --gpu-memory-utilization 0.95`

## Verified Hardware & Cloud Pathways
- Amazon Hardware: [RTX 5060 Ti 16GB graphics card](https://www.amazon.com/s?k=RTX+5060+Ti+16GB+graphics+card&tag=sparecables-20) (rel="noopener sponsored")
- RunPod Cloud Rental: [Deploy Instance](https://runpod.io?ref=ynypzu94) (rel="noopener sponsored")
- Vast.ai Cloud Rental: [Deploy Instance](https://cloud.vast.ai/?ref_id=723130) (rel="noopener sponsored")

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*Interactive Sizing Calculator available at: https://www.gpugarden.com/vram/gpt-oss-20b/*