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Head-to-head comparison

GPT-5.5 vs gpt-oss-120b

GPT-5.5 (OpenAI) and gpt-oss-120b (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-5.5 holds the stronger ModelCap Index position (#13 vs #132); gpt-oss-120b is 50× cheaper per output token ($0.60/1M vs $30.00/1M); GPT-5.5 offers the longer context window (1M vs 131K tokens); and gpt-oss-120b ships open weights.

Which should you choose?

Choose GPT-5.5 if…

  • you want the stronger overall ModelCap Index position — #13 against #132 (82.5 vs 43.3 points).
  • you need the longer context window — 1M tokens against 131K.
  • Arena coding is your yardstick — 1520 against 1391.
  • AA Intelligence Index is your yardstick — 38.4 against 11.6.
  • AA τ²-Bench Telecom is your yardstick — 93.9% against 65.8%.
  • AA Humanity's Last Exam is your yardstick — 45.8% against 19.6%.
  • you want the more recently listed model — GPT-5.5 was listed 24 April 2026, gpt-oss-120b 5 August 2025.

Choose gpt-oss-120b if…

  • API cost matters — $0.60/1M output tokens against $30.00/1M, about 50× cheaper.
  • your workload is prompt-heavy — input tokens cost $0.15/1M against $5.00/1M.
  • you want to self-host: gpt-oss-120b ships open weights while GPT-5.5 is api only.
  • you want provider choice — 20 listed API providers against 3.

GPT-5.5 vs gpt-oss-120b: specs, pricing and context

Specification comparison of GPT-5.5 and gpt-oss-120b
FieldGPT-5.5OpenAIgpt-oss-120bOpenAI
ModelCap Index position#13#132
Index score82.543.3
EvidenceMeasuredMeasured
Input price / 1M tokens$5.00$0.15
Output price / 1M tokens$30.00$0.60
Context window1M tokens131K tokens
Max output tokens128K66K
API providers listed320
Weight accessAPI onlyOpen weights
Input modalitiesFile, Image, TextText
First listed24 April 20265 August 2025
PublisherOpenAIOpenAI

Evidence: 7 public benchmark observations across 7 boards · 3 public benchmark observations across 3 boards. Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.

Benchmark scores: GPT-5.5 vs gpt-oss-120b

Public benchmark boards where GPT-5.5 or gpt-oss-120b has a published result
BoardGPT-5.5gpt-oss-120bLeads
Arena codingArena (LMArena)15201514–1526High13911383–1398GPT-5.5
LMArena AgentLMArena5.0%4.1%–6.0%X-High—Only one result
ARC-AGI-2ARC Prize Foundation85.0%X-High—Only one result
ARC-AGI-3ARC Prize Foundation0.4%High—Only one result
SWE-benchSWE-bench (Princeton / SWE-agent team)—26.0%Only one result
AA Intelligence IndexArtificial Analysis38.4intelligence-index:v4.3:xhigh11.6intelligence-index:v4.3:highGPT-5.5
AA τ²-Bench TelecomArtificial Analysis93.9%tau2:telecom:dual-control:pass-at-1:3-repeats:source-model="GPT-5.5 (xhigh)":reasoning=true65.8%tau2:telecom:dual-control:pass-at-1:3-repeats:source-model="gpt-oss-120b (high)":reasoning=trueGPT-5.5
AA Humanity's Last ExamArtificial Analysis45.8%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="GPT-5.5 (xhigh)":reasoning=true19.6%hle:may-2025:text-only-2158:no-tools:pass-at-1:source-model="gpt-oss-120b (high)":reasoning=trueGPT-5.5
Terminal-Bench 2.1 Terminus 2Terminal-Bench78.0X-High—Only one result
WildClawBench OpenClawWildClawBench58.2—Only one result

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.

GPT-5.5 vs gpt-oss-120b: common questions

Is GPT-5.5 better than gpt-oss-120b?

GPT-5.5 ranks higher on the ModelCap Index as of 22 September 2026: #13 against #132. 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.

Is GPT-5.5 cheaper than gpt-oss-120b?

gpt-oss-120b is cheaper on output tokens: $0.60/1M against $30.00/1M. Input tokens are $5.00/1M for GPT-5.5 and $0.15/1M for gpt-oss-120b. 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 $25.00 for GPT-5.5 versus $0.60 for gpt-oss-120b. gpt-oss-120b costs 97.6% less in this scenario. This excludes caching, batch discounts, prompt-length tiers, tool charges and retries; verify the selected endpoint before budgeting.

Which has the bigger context window, GPT-5.5 or gpt-oss-120b?

GPT-5.5 has the larger context window: 1M tokens against 131K.

Which is better for coding, GPT-5.5 or gpt-oss-120b?

Arena coding: GPT-5.5 1520, gpt-oss-120b 1391 — GPT-5.5 leads.

Are GPT-5.5 and gpt-oss-120b open-weight models?

GPT-5.5: API only. gpt-oss-120b: 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.

Where can I run GPT-5.5 and gpt-oss-120b?

ModelCap currently lists 3 API providers for GPT-5.5 and 20 for gpt-oss-120b, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.

How current is this GPT-5.5 vs gpt-oss-120b comparison?

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.

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