How Much VRAM Does gpt-oss 20B Need to Run Locally?
See devices that run itgpt-oss 20B is a MoE model with 20.9B total parameters and 3.6B active per token. At Q4 it needs 14GB of VRAM to sit entirely on the GPU; with experts offloaded to system RAM it needs only 4GB of VRAM plus 12GB of RAM. The cheapest device that holds it is the GeForce RTX 4080, with no used-price data yet, at roughly 118.2 tokens/s.
gpt-oss 20B details
VRAM needed for gpt-oss 20B by quantization and context
Total at 8KMoE: all 20.9B parameters must stay resident in memory, while speed is set by the 3.6B active per token.
| Quantization | WeightsGB | Total at 8KGB | Total at 32KGB | Total at 128KGB |
|---|---|---|---|---|
| Q4_K_M | 11.6GGUF | 13 | 14.2 | 18.7 |
| Q5_K_M | 11.7GGUF | 15.5 | 16.6 | 21.1 |
| Q8_0 | 12.1GGUF | 23 | 24.2 | 28.7 |
| FP16 | 13.8GGUF | 42.3 | 43.4 | 47.9 |
Total = weights + KV cache (FP16) + 1GB runtime overhead. Weights marked GGUF are measured file sizes from the repository; the rest are estimated from bytes per parameter. Contexts beyond this model's 128K limit show a dash.
Which GPUs can run gpt-oss 20B?
Q4_K_M · 8K context · sorted by eBay used price| Device | VRAMGB | Used price | Est. t/s | Suggested context |
|---|---|---|---|---|
 GeForce RTX 4080 | 16 | —No listings | 118.2 | 32K |
| GeForce RTX 5070 Ti | 16 | —No listings | 132.1 | 32K |
| GeForce RTX 5080 | 16 | —No listings | 136.4 | 32K |
 Radeon RX 9070 XT | 16 | —No listings | 90.9 | 32K |
| Radeon RX 7900 XT | 20 | —No listings | 104.2 | 128K |
 Arc Pro B60 | 24 | —No listings | 67.1 | 128K |
| GeForce RTX 3090 | 24 | —No listings | 134.8 | 128K |
| GeForce RTX 4090 | 24 | —No listings | 139.4 | 128K |
| GeForce RTX 5090 D V2 | 24 | —No listings | 156.7 | 128K |
| Radeon RX 7900 XTX | 24 | —No listings | 115.4 | 128K |
| RTX PRO 4000 Blackwell | 24 | —No listings | 114.1 | 128K |
| Arc Pro B65 | 32 | —No listings | 82.1 | 128K |
| Arc Pro B70 | 32 | —No listings | 82.1 | 128K |
| GeForce RTX 4080 SUPER 32GB (modded) | 32 | —No listings | 119.8 | 128K |
| GeForce RTX 5090 | 32 | —No listings | 172.9 | 128K |
| GeForce RTX 5090 D | 32 | —No listings | 172.9 | 128K |
| Instinct MI100 | 32 | —No listings | 130.8 | 128K |
| Radeon AI PRO R9700 | 32 | —No listings | 90.9 | 128K |
| Radeon PRO W7800 | 32 | —No listings | 84.9 | 128K |
| RTX PRO 4500 Blackwell | 32 | —No listings | 132.1 | 128K |
| A100 40GB PCIe | 40 | —No listings | 165.1 | 128K |
| GeForce RTX 4090 48GB (modded) | 48 | —No listings | 139.4 | 128K |
| Radeon PRO W7900 | 48 | —No listings | 108.9 | 128K |
| RTX PRO 5000 Blackwell 48GB | 48 | —No listings | 156.7 | 128K |
| Instinct MI210 | 64 | —No listings | 148.5 | 128K |
| RTX PRO 5000 Blackwell 72GB | 72 | —No listings | 156.7 | 128K |
| Mac Studio M4 Max 128GB | 128 | —No listings | 87.3 | 128K |
| Mac Studio M3 Ultra 256GB | 256 | —No listings | 111.5 | 128K |
| Mac Studio M3 Ultra 512GB | 512 | —No listings | 111.5 | 128K |
Fits when weights + KV cache + runtime overhead is at or below usable memory, single card. "Offload" on MoE models means it runs with expert weights in system RAM (only attention layers and KV cache stay in VRAM); that speed assumes 70 GB/s RAM bandwidth. The context column is the largest tier that fits.
Run gpt-oss 20B with Ollama, llama.cpp or vLLM
Ollama pulls and runs it in one command; the quantization comes from the official tag.
ollama run gpt-oss:20b
llama.cpp pulls the GGUF straight from Hugging Face; -c sets the context length.
llama-server -hf unsloth/gpt-oss-20b-GGUF:Q4_K_M -c 8192
vLLM serves the original-precision weights, which needs far more memory than GGUF and usually more than one GPU.
vllm serve openai/gpt-oss-20b
File names follow that week's model-library snapshot; the definitions are in the methodology. Methodology
FAQ
How much VRAM does gpt-oss 20B need?
At Q4_K_M with an 8K context gpt-oss 20B needs about 14GB of VRAM; 16GB leaves comfortable headroom.
What is the cheapest GPU that runs gpt-oss 20B?
The GeForce RTX 4080: 16GB of VRAM at roughly 118.2 tokens/s. We have no used-price data for it yet.
Can you run gpt-oss 20B with Ollama?
Yes: ollama run gpt-oss:20b.