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OpenAI: gpt-oss-20b (free)

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

Tokenizer lineage (measured): GPT
Declared tokenizer tag: GPT
Entered catalogue: 5 August 2025
Measurement: Variant: inherits its base model’s measurement
Evidence confidence: High

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

Evidence

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

Compare with OpenAI: gpt-oss-20b

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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.

What we checked

Four different kinds of evidence, and what each one showed

We checked	What we found	Where it came from
How it counts tokens	Not measured yet	we measured it
How its API is set up	A combination of settings no other listing in the catalogue uses	api_2d48d2cb
How much it can read and write	Reads up to 131,072 tokens at once, writes up to 32,768	its own listing
Whether it thinks before answering	Always reasons, and cannot be turned off, at high, medium, low, medium by default	its own listing

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.

* OpenAI: gpt-oss-20b (free) no longer appears in the OpenRouter catalogue, first absent from the snapshot of 3 September 2026. The record stays because the measurements above were real when they were taken and this address has been published.