Model record
gpt-oss-20b
OpenAI · Apache 2.0 · verified
What this model is
OpenAI reports 21B total parameters and 3.6B active parameters per token.
The architecture is mixture of experts. Memory must hold the full weight set, while active parameters affect the speed heuristic. Experts can be offloaded to system memory, but that trades speed for capacity.
Memory and quantization
Decimal GB. The MXFP4 GGUF file is 12.11 GB; the checked GGUF repository does not publish a separate Q8 build.
| Quantization | Published files | 8K estimate |
|---|---|---|
| MXFP4 | 12.11 GB | 13.81 GB |
Estimate formula: published weight files + 0.2045 GB per 8K tokens × context / 8K + 1.5 GB runtime overhead. Sizes are decimal GB, not GiB. At 8K context, the smallest listed build is about 13.8 GB before OS and application reserve.
Conservative FP16 estimate from the public config. Alternating full-attention layers use 8 KV heads; local layers are capped by a 128-token sliding window.
KV method source: https://huggingface.co/openai/gpt-oss-20b/raw/main/config.json
Speed heuristic
Not benchmarked here. The calculator labels relative speed from active parameter count only.
Active path: 3.6B parameters. This is a relative speed signal only; it is not a tokens/sec benchmark.
If the full weights do not fit in accelerator memory but do fit in system memory, the calculator marks the result as a tight CPU-offload fit. Expect substantially slower generation and verify the runtime's MoE offload support.
Runtimes
- Ollama
- llama.cpp
- vLLM
ollama run gpt-oss:20bLicense restrictions
Apache 2.0 permits commercial use and modification; retain notices and comply with the patent and termination terms.
This is a plain-language summary, not legal advice. Read the linked license before commercial deployment or redistribution.
Known issues
- The Harmony response format is required; using an unrelated chat format can produce incorrect output.
- OpenAI's 16 GB guidance is for the MXFP4 build and does not guarantee room for a long context.
Sources
- https://huggingface.co/openai/gpt-oss-20b
- https://huggingface.co/ggml-org/gpt-oss-20b-GGUF
- https://ollama.com/library/gpt-oss
- https://huggingface.co/openai/gpt-oss-20b/raw/main/config.json
This page is an independent compatibility guide, not official documentation. Verify the primary source before downloading or deploying a model.