Head-to-head comparison
gpt-oss-120b (OpenAI) and gpt-oss-20b (OpenAI) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.
Snapshot as of 22 September 2026
As of 22 September 2026, gpt-oss-120b holds the stronger ModelCap Index position (#132 vs #163); and gpt-oss-20b is 6.7× cheaper per output token ($0.09/1M vs $0.60/1M).
Evidence: 3 public benchmark observations across 3 boards · 3 public benchmark observations across 3 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.
Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.
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gpt-oss-120b ranks higher on the ModelCap Index as of 22 September 2026: #132 against #163. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.
gpt-oss-20b is cheaper on output tokens: $0.09/1M against $0.60/1M. Input tokens are $0.15/1M for gpt-oss-120b and $0.018/1M for gpt-oss-20b. Prices are the lowest listed API offer ModelCap observed, in USD per million tokens. For 1,000 requests with 2,000 input and 500 output tokens each (2M input + 0.5M output), the listed-rate estimate is $0.60 for gpt-oss-120b versus $0.08 for gpt-oss-20b. gpt-oss-20b costs 86.5% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.
Both publish a 131K-token context window.
Arena coding: gpt-oss-120b 1391, gpt-oss-20b 1369 — gpt-oss-120b leads.
gpt-oss-120b: Open weights. gpt-oss-20b: Open weights. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.
ModelCap currently lists 20 API providers for gpt-oss-120b and 11 for gpt-oss-20b, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.
Every figure comes from the sealed ModelCap dataset published 22 September 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.