OpenAI: GPT-5.6 Luna Pro vs SpaceXAI: Grok 4.20
Side-by-side comparison of specs, pricing, benchmark scores, and task rankings. Updated 2026-11-07.
| OpenAI: GPT-5.6 Luna Pro | SpaceXAI: Grok 4.20 | |
|---|---|---|
| Vendor | openai | x-ai |
| Quality Score | 100 | 100 |
| Benchmark Score | - | 56.5 |
| Input Price | $0.20/M | $1.25/M |
| Output Price | $1.20/M | $2.50/M |
| Context Window | 1,050,000 | 2,000,000 |
| Max Output | 128,000 | 1,800,000 |
| Tool Calling | ✓ | ✓ |
| Structured Output | ✓ | ✓ |
| Reasoning Mode | ✓ | ✓ |
| Vision | ✓ | ✓ |
| Audio | - | - |
| Benchmark Scores | ||
| ai_index | - | 61.0 |
| eqbench | - | 45.7 |
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 Grok 4.20 costs $1.88, so GPT-5.6 Luna Pro is about 3.8 times cheaper for the same work.
Grok 4.20 reads up to 2,000,000 tokens at once, roughly 3,000 pages of text, against about 1,575 pages for GPT-5.6 Luna Pro.
Across the 20 tasks where they differ, GPT-5.6 Luna Pro scores higher on 4 (Code Completion, JSON Extraction, Bulk Data Labeling and others), Grok 4.20 on 16 (SQL Generation, Code Review, Code Refactoring and others).
GPT-5.6 Luna Pro was released in July 2026 and Grok 4.20 in March 2026.
Pick GPT-5.6 Luna Pro if you need lower cost; pick Grok 4.20 if you need long documents 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 | SpaceXAI: Grok 4.20 |
|---|---|---|
| SQL Generation | 133 | 144 |
| Code Review | 132 | 149 |
| Code Completion | 131 | 121 |
| Code Refactoring | 136 | 151 |
| Bug Fixing | 136 | 153 |
| Unit Test Generation | 124 | 134 |
| Code Documentation | 131 | 140 |
| Regex Writing | 119 | 127 |
| CI/CD Pipelines | 120 | 130 |
| Frontend Component Design | 122 | 131 |
| Data Analysis | 124 | 135 |
| CSV / Spreadsheet Cleanup | 133 | 138 |
| ETL Scripting | 128 | 141 |
| JSON Extraction | 131 | 123 |
| Bulk Data Labeling | 129 | 120 |
| OCR / Document Parsing | 131 | 135 |
| Table Extraction from PDFs | 131 | 135 |
| Long-Document Summarization | 137 | 153 |
| Short-Form Summarization | 123 | 119 |
| Blog Post Writing | 121 | 132 |
Scores reflect capability match + benchmark data + pricing for each task. Methodology →