# GPT OSS 20B

GPT OSS 20B is a text generation model from OpenAI, available through the Impossibl API. Its published context window is 128,000 tokens. The advertised input rate is $0.075 per million input tokens. The advertised output rate is $0.30 per million output tokens.

- Model identifier: ` openai/gpt-oss-20b `
- Creator: OpenAI
- Model type: Text generation
- Canonical model page: [GPT OSS 20B](<https://impossibl.com/openai/gpt-oss-20b>)
- API availability: Listed as serving through Impossibl.
- Creator release date: 2025-08-05

## Capabilities and limits

- Context window: 128,000 tokens
- Maximum output tokens: Not published in the public catalog; this is separate from the context window.
- Inputs: text
- Outputs: text
- Tool calling: Not published

## API access

Use ` openai/gpt-oss-20b ` as the model identifier through the Impossibl API.

Published API endpoints:

- ` /v1/chat/completions `

[API quickstart](<https://impossibl.com/docs/agent-quickstart>) · [Models and billing documentation](<https://impossibl.com/docs/models>)

## Published API prices

All rates are in USD. An unpublished rate is unknown, not zero. Workspace-specific pricing, taxes, balance-purchase fees, billing adjustments, and tool charges can affect the amount paid.

| Usage | Published base rate | Billing unit |
| --- | --- | --- |
| Input | $0.075 | per million input tokens |
| Output | $0.30 | per million output tokens |
| Cache read | $0.0375 | per million cached input tokens |
| Cache write (default retention) | Not published | per million tokens |
| Cache write (one-hour retention) | Not published | per million tokens |
| Audio input | Not published | per million audio input tokens |

## Independent benchmarks

Source: [Artificial Analysis](<https://artificialanalysis.ai/>). Last checked: 2026-09-11T10:50:14.034Z.
Configurations are evaluated separately. API scores retain their original units. Unmeasured scores are omitted.

### gpt-oss-20b (high)

Source: [Evaluation source](<https://artificialanalysis.ai/models/gpt-oss-20b>)

| Benchmark | Score |
| --- | --- |
| Intelligence Index | 9.04 |
| Omniscience Index | -63.05 |
| GPQA | 68.79% |
| Humanity’s Last Exam | 10.98% |
| SciCode | 38.89% |
| CritPt | 1.43% |
| Terminal-Bench v2.1 | 13.86% |
| Terminal-Bench v4.0 | 0.00% |
| Terminal-Bench Hard | 10.61% |
| AA-LCR | 34.67% |
| Multilingual LCR | 0.56% |
| GDPval Elo | 513.93 |
| GDP.pdf All-pass | 2.00% |
| AutomationBench Partial | 0.19% |
| IFBench | 65.10% |
| Tau2 | 60.23% |
| Tau Banking | 7.01% |
| APEX-Agents | 0.74% |
| LiveCodeBench | 77.67% |
| AIME 2025 | 89.33% |
| coding index (API) | 20.7 |
| agentic index (API) | 1.4 |
| intelligence index (API) | 9 |

### gpt-oss-20b (low)

Source: [Evaluation source](<https://artificialanalysis.ai/models/gpt-oss-20b-low>)

| Benchmark | Score |
| --- | --- |
| Intelligence Index | 9.95 |
| Omniscience Index | -58.55 |
| GPQA | 61.11% |
| Humanity’s Last Exam | 5.28% |
| CritPt | 0.00% |
| Terminal-Bench Hard | 4.55% |
| AA-LCR | 31.00% |
| IFBench | 57.82% |
| Tau2 | 50.29% |
| LiveCodeBench | 65.19% |
| AIME 2025 | 62.33% |
| intelligence index (API) | 10 |

Full benchmark data and breakdowns: [Complete benchmark snapshot](<https://api.impossibl.com/v1/models/openai/gpt-oss-20b/benchmarks>).


## Availability and retirement

The model is listed as serving. No retirement is announced in the current public catalog.

## Frequently asked questions

### What is GPT OSS 20B?

GPT OSS 20B is a text-generation model from OpenAI, available through the Impossibl API.

### How much does GPT OSS 20B cost?

GPT OSS 20B costs $0.075 per million input tokens and $0.30 per million output tokens through the Impossibl API. Cache reads cost $0.0375 per million tokens. All rates are in USD.

### What is the context length of GPT OSS 20B?

GPT OSS 20B has a 128,000-token context window through the Impossibl API.

### What inputs and outputs does GPT OSS 20B support?

GPT OSS 20B accepts text as input. GPT OSS 20B returns text.

### How do I use GPT OSS 20B through an API?

GPT OSS 20B is available through the Impossibl API. Use openai/gpt-oss-20b as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request.

### When was GPT OSS 20B released?

OpenAI released GPT OSS 20B on August 5, 2025.

Sources: [Creator release announcement](<https://openai.com/index/introducing-gpt-oss/>)

## Sources and related links

Prices, limits, capabilities, endpoints, and availability come from the public Impossibl catalog. Creator documentation supplies descriptions and release dates where available; it does not override the published API offering.

- [Public Impossibl model catalog](<https://api.impossibl.com/v1/models>)
- [Full model directory as JSON](<https://impossibl.com/models.json>)
- [GPT OSS 20B: model details and pricing](<https://impossibl.com/openai/gpt-oss-20b>)
- [Model directory](<https://impossibl.com/models>)