GPT-5.6 Luna Pro vs Grok 4.20
How do these models stack up? Below is an expert side-by-side comparison of specifications, context window capacity, live pricing per million tokens, and standardized benchmark scores for GPT-5.6 Luna Pro and Grok 4.20.
GPT-5.6 Luna Pro
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://developers.openai.com/api/docs/guides/reasoning#reasoning-mode
Grok 4.20
Grok 4.20 is xAI's most advanced reasoning model, combining powerful analytical capabilities with unique real-time integration to the X (formerly Twitter) platform data stream. This live data access allows Grok 4.20 to answer queries with up-to-the-minute context, making it invaluable for financial analysis, current events research, and real-time market monitoring. Exceptionally strong in physics, advanced mathematics, and code synthesis, it operates with a 2-million-token context window and is priced at $1.25/MTok for input — delivering frontier-tier reasoning at a highly competitive cost for developers building intelligent agents and analytical tools.
Technical Specifications
| Specification | GPT-5.6 Luna Pro | Grok 4.20 |
|---|---|---|
| Provider | OpenAI | xAI |
| Context Window | 1,050,000 tokens | 2,000,000 tokens |
| Agent Suitability | N/A | 90/100 |
| Time to First Token (TTFT) | N/A | 350 ms |
| Deployment Model | managed api | managed api |
| Production Stability | beta | stable |
| API Available | Yes | Yes |
| Released Date | 2026-07-09 | 2026-05-05 |
API Pricing Comparison
Input Price per Million Tokens
GPT-5.6 Luna Pro
$1.00
Grok 4.20
$1.25
Output Price per Million Tokens
GPT-5.6 Luna Pro
$6.00
Grok 4.20
$2.50
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Benchmark Performance Metrics
Scores show the raw performance percentages verified across key evaluation suites. Higher bars indicate superior accuracy and capability in that domain.
GPT-5.6 Luna Pro Quirks & Gotchas
No developer gotchas reported.
Grok 4.20 Quirks & Gotchas
- ▸Real-time X data access — unparalleled for current events / financial analysis
- ▸Tool calling API is still maturing — test thoroughly for production agentic use