Head-to-head comparison
gpt-oss-20b (OpenAI) and o4 Mini (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, o4 Mini holds the stronger ModelCap Index position (#107 vs #163); gpt-oss-20b is 48.9× cheaper per output token ($0.09/1M vs $4.40/1M); o4 Mini offers the longer context window (200K vs 131K tokens); and gpt-oss-20b ships open weights.
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.
Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.
o4 Mini ranks higher on the ModelCap Index as of 22 September 2026: #107 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 do not overlap, but the aggregate Index does not predict performance on every task; compare the relevant benchmark configurations before choosing.
gpt-oss-20b is cheaper on output tokens: $0.09/1M against $4.40/1M. Input tokens are $0.018/1M for gpt-oss-20b and $1.10/1M for o4 Mini. 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 $0.08 for gpt-oss-20b versus $4.40 for o4 Mini. gpt-oss-20b costs 98.2% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.
o4 Mini has the larger context window: 200K tokens against 131K.
Arena coding: gpt-oss-20b 1369, o4 Mini 1433 — o4 Mini leads.
gpt-oss-20b: Open weights. o4 Mini: API only. 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 11 API providers for gpt-oss-20b and 1 for o4 Mini, 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.