GPT-5.5 is OpenAI’s frontier model designed for complex professional workloads, building on GPT-5.4 with stronger reasoning, higher reliability, and improved token efficiency on hard tasks. It features a 1M+ token...
Model details →OpenAI: GPT-5.5 vs OpenAI: GPT-5.6 Luna Pro
OpenAI: GPT-5.6 Luna Pro wins on 2 of 6 axes — pricing and capability skew in its favour for most workloads.
GPT-5.6 Luna Pro is the same underlying model as [GPT-5.6 Luna](https://openrouter.ai/openai/gpt-5.6-luna), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. Learn more in OpenAI's docs: https://devel…
Model details →Side-by-side comparison
| Capability | OpenAI: GPT-5.5 | OpenAI: GPT-5.6 Luna Pro | Winner |
|---|---|---|---|
| Context window Maximum number of input tokens the model can attend to in a single request. | 1.1M | 1.1M | Tie |
| Input price (per 1M) Cost per million input tokens billed by the provider. | $5.00 | $0.10 | 🏆 OpenAI: GPT-5.6 Luna Pro |
| Output price (per 1M) Cost per million output tokens billed by the provider. | $30.00 | $0.60 | 🏆 OpenAI: GPT-5.6 Luna Pro |
| Tool / function calling First-class support for emitting structured tool calls. | Yes | Yes | Tie |
| Vision input Accepts image inputs alongside text. | Yes | Yes | Tie |
| Reasoning mode Internal chain-of-thought / extended-thinking support. | Yes | Yes | Tie |
Frequently asked questions
Is OpenAI: GPT-5.5 better than OpenAI: GPT-5.6 Luna Pro?
OpenAI: GPT-5.6 Luna Pro wins on 2 of 6 axes — pricing and capability skew in its favour for most workloads.
What's the price difference between OpenAI: GPT-5.5 and OpenAI: GPT-5.6 Luna Pro?
Input: $5.00 vs $0.10 per 1M tokens. Output: $30.00 vs $0.60 per 1M tokens.
What context windows do OpenAI: GPT-5.5 and OpenAI: GPT-5.6 Luna Pro support?
OpenAI: GPT-5.5 supports up to 1.1M tokens. OpenAI: GPT-5.6 Luna Pro supports up to 1.1M tokens.
Do both OpenAI: GPT-5.5 and OpenAI: GPT-5.6 Luna Pro support tool calling?
OpenAI: GPT-5.5: yes. OpenAI: GPT-5.6 Luna Pro: yes.
Compare OpenAI: GPT-5.5 with other models
vs Anthropic Claude Haiku Latestvs Anthropic Claude Sonnet Latestvs Anthropic: Claude Fable Latestvs Anthropic: Claude Opus Latest