OpenAI: gpt-oss-20b (free)

openai/gpt-oss-20b:free · OpenAIDeclared and measured agree

Tokenizer lineage (measured): GPT
Evidence confidence: High
Declared tokenizer tag: GPT
Entered catalogue: 5 August 2025
Last tested: Not yet measured
Measurement: Variant: inherits its base model’s measurement

Evidence

✓ inherited from openai/gpt-oss-20b: a serving variant shares its base model's tokenizer

This entry is a serving variant of OpenAI: gpt-oss-20b. A variant shares its base model's tokenizer by construction, so the measurement lives on the base record and this page inherits it.

Identity statement

OpenAI: gpt-oss-20b (free) is OpenAI's model. Its measured tokenizer sits with the GPT group, which is evidence that it builds on the GPT tokenizer. Tokenizer reuse is normal engineering, open vocabularies travel between labs, and this says nothing against OpenAI's authorship of the model itself.

Evidence stack

Signals of different kinds, weighed together

Signal	Result	Reference
Tokenizer signature	Not measured	–
API surface	No other entry shares this exact contract	api_2d48d2cb
Context and output	131,072 context · 32,768 max output	declared
Reasoning contract	Mandatory · efforts high, medium, low · default medium	declared
Serving providers observed	None recorded yet	–

Declared record

What the catalogue claims about this model

gpt-oss-20b is an open-weight 21B parameter model released by OpenAI under the Apache 2.0 license. It uses a Mixture-of-Experts (MoE) architecture with 3.6B active parameters per forward pass, optimized for...

Modalities: text->text
Declared tokenizer: GPT
Prompt price: $0 / M tokens
Completion price: $0 / M tokens

Supported parameters

frequency_penaltyinclude_reasoninglogprobsmax_tokenspresence_penaltyreasoningreasoning_effortrepetition_penaltyresponse_formatseedstopstructured_outputstemperaturetool_choicetoolstop_ktop_logprobstop_p

defaults: {"temperature":null,"top_p":null,"frequency_penalty":null}

Catalogue entry Weights on Hugging Face

History

Every observation, kept as taken

5 August 2025Enters the OpenRouter catalogue declared as GPT.

Cite this page as the evidence record for OpenAI: gpt-oss-20b (free): the URL is stable, measurements are dated, and revisions append to the history above. Method: tokenizer fingerprinting, v1, 50 strings. The raw data behind every figure is on the data page.