Grok 3 vs GPT-5.6 Luna
Detailed pricing comparison and cost analysis.
Updated September 2026
Cost Simulator
| Feature | Grok 3 | GPT-5.6 Luna |
|---|---|---|
| Provider | xAI | OpenAI |
| Input Price (1M) | $3.00 | $0.20 |
| Output Price (1M) | $15.00 | $1.20 |
| Context Window | 131,000 | 1,000,000 |
Verdict
Grok 3 costs $3.00 per 1M input tokens and $15.00 per 1M output tokens. GPT-5.6 Luna costs $0.20 per 1M input tokens and $1.20 per 1M output tokens. GPT-5.6 Luna is 93% cheaper on input tokens than Grok 3. For output tokens, GPT-5.6 Luna is the more affordable option at $1.20/1M vs $15.00.
On context window, GPT-5.6 Luna supports 1,000,000 tokens — meaning it can fit more conversation history, documents, or code in a single request. This matters for RAG pipelines, long document analysis, and agentic workflows where context builds up over many turns.
When to choose Grok 3
- ✓ You are already integrated with xAI
When to choose GPT-5.6 Luna
- ✓ You need the lowest input token cost ($ 0.20/1M)
- ✓ Your workload is output-heavy — GPT-5.6 Luna generates text cheaper
- ✓ You need a larger context window (1,000,000 tokens)
- ✓ You are already integrated with OpenAI
Use the calculator above to simulate your specific workload and find the exact break-even point. For most applications, the cheapest model is the one that minimises your total monthly bill given your input-to-output token ratio.
Frequently Asked Questions
Is Grok 3 cheaper than GPT-5.6 Luna? ▼
GPT-5.6 Luna is cheaper on input tokens at $0.20/1M vs $3.00/1M for Grok 3 — a 93% saving.
What is the context window of Grok 3 vs GPT-5.6 Luna? ▼
Grok 3 has a 131,000-token context window. GPT-5.6 Luna has a 1,000,000-token context window. GPT-5.6 Luna supports the larger context, suitable for longer documents and agentic workflows.
Which model is better: Grok 3 or GPT-5.6 Luna? ▼
The best choice depends on your use case. For cost efficiency on input tokens, GPT-5.6 Luna is the cheaper option. For maximum context length, GPT-5.6 Luna supports 1,000,000 tokens. Use the comparison table above to find the right fit for your workload.