GPT-5.5 Pro
GPT-5.5 Pro is an API-only (closed weights) language model from OpenAI, released April 23, 2026. The context window is 1.1M tokens. On the Epoch Capabilities Index it scores 162.7, rank 14 of 256 rated models. API price: $30 input / $180 output per million tokens.
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Lab
OpenAI
Released
April 23, 2026
Weights
API-only (closed weights)
Parameters
–
Context
1.1M
Price / M tokens
$30 / $180 in / out
Epoch ECI
162.7 #14
Strengths by category
ModelTape's 0–100 fit on Epoch AI benchmark results.
| Category | Score | Based on |
|---|---|---|
| Reasoning | 36.0 | Chess Puzzles, SimpleBench |
| Math | 71.1 | OTIS Mock AIME 2024-2025, FrontierMath-Tiers-1-3-v2-Private, FrontierMath-Tier-4-v2-Private |
Benchmark results
| Benchmark (Epoch AI) | Score |
|---|---|
| OTIS Mock AIME | 100.0% |
| GPQA Diamond | 95.7% |
| FrontierMath (Tiers 1–3) | 92.3% |
| FrontierMath-Tier-4-v2-Private | 78.0% |
| SimpleBench | 72.3% |
| Chess Puzzles | 60.0% |
Links
Announcement · Epoch AI benchmarks
Models with a similar score
Claude Sonnet 5.5 · Gemini 4 Argon · Claude Opus 5 · Claude Fable 5 · GPT-6 Sol · GPT-5.6 Sol · Muse Wonder · Kimi K3.1 Pro
More from OpenAI
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