In short
How they differ.
Worked out from the figures below. Prices and specs are the makers' own, read Oct 20, 2026.
- Claude Sonnet 5.5 reads more at once: a context window of 1M tokens against 128K.
- gpt-oss-120b can be downloaded and run on your own machine; Claude Sonnet 5.5 can't.
- No independent board we follow ranks both models yet.
Side by side
The specs.
| Claude Sonnet 5.5 | gpt-oss-120b | |
|---|---|---|
| Made by | Anthropic · US | OpenAI · US |
| Released | Sep 28, 2026 | Aug 5, 2025 |
| Price per 1M tokens | $2 in / $10 out | Free to download; hosts set prices |
| Context window | 1M | 128K |
| Takes in | text, image | text |
| Download and run it yourself | No | Yes (Apache 2.0) |
| Size | Not published | 117B parameters, 5.1B active |
| Maker says | “High-performance model for coding and agents” | “production, general purpose, high reasoning use cases” |
| Sources | Prices, Oct 20, 2026 · Description | Prices, Oct 20, 2026 · Description |
Independent tests
Where they place.
Position on each board we follow (1 is best). Epoch AI's and Vectara's scores are shown; the other boards are linked for their own figures.
| Board | Claude Sonnet 5.5 | gpt-oss-120b |
|---|---|---|
| Epoch Capabilities IndexEpoch AI, Oct 20, 2026 | #6164.45 | Not listed |
| LMArena WebDevLMArena, Oct 19, 2026 | #3 | Not listed |
| LMArena mathLMArena, Oct 15, 2026 | #15 | Not listed |
| LMArena Agent ArenaLMArena, Oct 19, 2026 | #5 | Not listed |
| Humanity's Last ExamScale AI | #6 | Not listed |
| SWE-Bench ProScale AI, Sep 22, 2026 | #8 | Not listed |
| Vals IndexVals AI, Oct 19, 2026 | #1 | Not listed |
| Terminal-Bench 4.0Vals AI, Oct 19, 2026 | #2 | Not listed |
| Vibe Code BenchVals AI, Oct 18, 2026 | #1 | Not listed |
| ProofBenchVals AI, Oct 12, 2026 | #1 | Not listed |
| Vectara hallucination testVectara, Oct 16, 2026 | Not listed | #9214.2% |
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