OpenAI: GPT-5.6 Luna 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 | SpaceXAI: Grok 4.20 | |
|---|---|---|
| Vendor | openai | x-ai |
| Quality Score | 100 | 100 |
| Benchmark Score | 89.4 | 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 | 84.5 | 61.0 |
| ai_index_agentic | 75.2 | - |
| ai_index_coding | 100.0 | - |
| eqbench | - | 45.7 |
The verdict
For a sample job of 1 million input tokens and 250,000 output tokens, GPT-5.6 Luna costs $0.50 and Grok 4.20 costs $1.88, so GPT-5.6 Luna 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.
On our blended benchmark score GPT-5.6 Luna leads 89.4 to 56.5.
Across the 20 tasks where they differ, GPT-5.6 Luna scores higher on 20 (SQL Generation, Code Review, Code Completion and others).
GPT-5.6 Luna was released in July 2026 and Grok 4.20 in March 2026.
Pick GPT-5.6 Luna if you need lower cost, benchmark performance or the stronger all-round task scores; pick Grok 4.20 if you need long documents.
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 | SpaceXAI: Grok 4.20 |
|---|---|---|
| SQL Generation | 171 | 144 |
| Code Review | 166 | 149 |
| Code Completion | 133 | 121 |
| Code Refactoring | 163 | 151 |
| Bug Fixing | 179 | 153 |
| Unit Test Generation | 154 | 134 |
| Code Documentation | 143 | 140 |
| Regex Writing | 136 | 127 |
| CI/CD Pipelines | 144 | 130 |
| Frontend Component Design | 146 | 131 |
| Data Analysis | 170 | 135 |
| CSV / Spreadsheet Cleanup | 154 | 138 |
| ETL Scripting | 154 | 141 |
| JSON Extraction | 149 | 123 |
| Bulk Data Labeling | 135 | 120 |
| OCR / Document Parsing | 146 | 135 |
| Table Extraction from PDFs | 146 | 135 |
| Long-Document Summarization | 159 | 153 |
| Short-Form Summarization | 132 | 119 |
| Blog Post Writing | 140 | 132 |
Scores reflect capability match + benchmark data + pricing for each task. Methodology →