OpenAI: GPT-5.6 Luna Pro vs Google: Gemini 3.5 Flash
Side-by-side comparison of specs, pricing, benchmark scores, and task rankings. Updated 2026-11-07.
| OpenAI: GPT-5.6 Luna Pro | Google: Gemini 3.5 Flash | |
|---|---|---|
| Vendor | openai | |
| Quality Score | 100 | 100 |
| Benchmark Score | - | 84.2 |
| Input Price | $0.20/M | $1.50/M |
| Output Price | $1.20/M | $9.00/M |
| Context Window | 1,050,000 | 1,048,576 |
| Max Output | 128,000 | 65,536 |
| Tool Calling | ✓ | ✓ |
| Structured Output | ✓ | ✓ |
| Reasoning Mode | ✓ | ✓ |
| Vision | ✓ | ✓ |
| Audio | - | ✓ |
| Benchmark Scores | ||
| ai_index | - | 82.8 |
| ai_index_agentic | - | 61.8 |
| ai_index_coding | - | 100.0 |
The verdict
For a sample job of 1 million input tokens and 250,000 output tokens, GPT-5.6 Luna Pro costs $0.50 and Gemini 3.5 Flash costs $3.75, so GPT-5.6 Luna Pro is about 7.5 times cheaper for the same work.
Both take in a similar amount of text: 1,050,000 and 1,048,576 tokens, about 1,575 and 1,573 pages.
Only Gemini 3.5 Flash offers audio input and video input.
Across the 20 tasks where they differ, GPT-5.6 Luna Pro scores higher on 3 (Code Completion, Bulk Data Labeling, Short-Form Summarization), Gemini 3.5 Flash on 17 (SQL Generation, Code Review, Code Refactoring and others).
GPT-5.6 Luna Pro was released in July 2026 and Gemini 3.5 Flash in May 2026.
Pick GPT-5.6 Luna Pro if you need lower cost; pick Gemini 3.5 Flash if you need audio input, video input or the stronger all-round task scores.
Costs use current list prices per million tokens; page counts assume about 0.75 words per token and 500 words per page.
Who wins by task?
| Task | OpenAI: GPT-5.6 Luna Pro | Google: Gemini 3.5 Flash |
|---|---|---|
| SQL Generation | 133 | 168 |
| Code Review | 132 | 164 |
| Code Completion | 131 | 119 |
| Code Refactoring | 136 | 162 |
| Bug Fixing | 136 | 176 |
| Unit Test Generation | 124 | 152 |
| Code Documentation | 131 | 141 |
| Regex Writing | 119 | 133 |
| CI/CD Pipelines | 120 | 143 |
| Frontend Component Design | 122 | 145 |
| Data Analysis | 124 | 167 |
| CSV / Spreadsheet Cleanup | 133 | 153 |
| ETL Scripting | 128 | 152 |
| JSON Extraction | 131 | 138 |
| Bulk Data Labeling | 129 | 124 |
| OCR / Document Parsing | 131 | 146 |
| Table Extraction from PDFs | 131 | 146 |
| Long-Document Summarization | 137 | 157 |
| Short-Form Summarization | 123 | 121 |
| Blog Post Writing | 121 | 138 |
Scores reflect capability match + benchmark data + pricing for each task. Methodology →