Z.ai: GLM 5.3 FlashX Legal vs OpenAI: GPT-6 Luna
Side-by-side comparison of specs, pricing, benchmark scores, and task rankings. Updated 2026-11-02.
| Z.ai: GLM 5.3 FlashX Legal | OpenAI: GPT-6 Luna | |
|---|---|---|
| Vendor | z-ai | openai |
| Quality Score | 100 | 100 |
| Input Price | $0.37/M | $0.10/M |
| Output Price | $1.25/M | $0.50/M |
| Context Window | 1,048,576 | 1,050,000 |
| Max Output | 131,072 | 128,000 |
| Tool Calling | ✓ | ✓ |
| Structured Output | ✓ | ✓ |
| Reasoning Mode | ✓ | ✓ |
| Vision | ✓ | ✓ |
| Audio | - | - |
The verdict
For a sample job of 1 million input tokens and 250,000 output tokens, GPT-6 Luna costs $0.23 and GLM 5.3 FlashX Legal costs $0.68, so GPT-6 Luna is about 3.0 times cheaper for the same work.
Both take in a similar amount of text: 1,048,576 and 1,050,000 tokens, about 1,573 and 1,575 pages.
Only GLM 5.3 FlashX Legal offers video input.
Across the 10 tasks where they differ, GPT-6 Luna on 10 (SQL Generation, Code Completion, Code Documentation and others).
GLM 5.3 FlashX Legal was released in November 2026 and GPT-6 Luna in September 2026.
Pick GLM 5.3 FlashX Legal if you need video input; pick GPT-6 Luna if you need lower cost 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 | Z.ai: GLM 5.3 FlashX Legal | OpenAI: GPT-6 Luna |
|---|---|---|
| SQL Generation | 133 | 133 |
| Code Completion | 131 | 131 |
| Code Documentation | 131 | 131 |
| Regex Writing | 119 | 119 |
| CSV / Spreadsheet Cleanup | 133 | 133 |
| JSON Extraction | 131 | 131 |
| Bulk Data Labeling | 129 | 129 |
| Long-Document Summarization | 137 | 137 |
| Short-Form Summarization | 123 | 123 |
| Blog Post Writing | 121 | 121 |
Scores reflect capability match + benchmark data + pricing for each task. Methodology →