GPT-5.6 Luna vs Grok 3
OpenAI vs xAI · Prices checked 12 August 2026
GPT-5.6 Luna is the cheaper of the two by a wide margin: $0.500 per million tokens blended against $6.60, roughly 13.2× less. A single 100K-input, 10K-output job costs $0.032 on GPT-5.6 Luna against $0.450 on Grok 3.
GPT-5.6 Luna leads on 2 of the 2 benchmarks both models report. The widest gap is on LMArena Elo, where GPT-5.6 Luna leads by 119 points. GPT-5.6 Luna takes a 1,050,000-token context window against 131,000, giving 8.0× more room for long documents or whole-codebase work.
Pricing and capacity
| Metric | GPT-5.6 Luna | Grok 3 | Difference |
|---|---|---|---|
| Input / 1M tokens | $0.200 | $3.00 | 15.0× |
| Output / 1M tokens | $1.20 | $15.00 | 12.5× |
| Blended · 70/30calculated | $0.500 | $6.60 | 13.2× |
| Blended · 50/50calculated | $0.700 | $9.00 | 12.9× |
| Blended · 80/20calculated | $0.400 | $5.40 | 13.5× |
| Blended · 20/80calculated | $1.00 | $12.60 | 12.6× |
| Job cost · 100K + 10Kcalculated | $0.032 | $0.450 | 14.1× |
| Job cost · 1M + 100Kcalculated | $0.320 | $4.50 | 14.1× |
| Context window | 1,050,000 | 131,000 | 8.0× |
Input and output rates are as published by each provider. Blended and job-cost rows are calculated comparison metrics, not published prices — how they are derived.
Benchmarks
| Benchmark | GPT-5.6 Luna | Grok 3 | Leader |
|---|---|---|---|
| GPQA Diamond | 92.3% | 75% | GPT-5.6 Luna |
| LMArena Elo | 1451 Elo | 1332 Elo | GPT-5.6 Luna |
Only suites both models report are listed, so a missing score is never shown as a loss. Figures are provider-published or from public leaderboards and are not independently re-run.
What each model is for
GPT-5.6 Luna
OpenAI · Efficient
The fastest and most affordable GPT-5.6 tier, a deliberately low-reasoning lane for high-volume work where speed and cost are the binding constraints rather than depth. It keeps the family's 1M-token context window at $0.20/$1.20 per MTok, which is 25× cheaper than Sol on input, with cached input at $0.02.
- Lowest cost in the GPT-5.6 family, 25× cheaper input than Sol
- Fast responses
- High-volume throughput
- 1M-token context
Frequently asked questions
Which is cheaper, GPT-5.6 Luna or Grok 3?
GPT-5.6 Luna is the cheaper of the two by a wide margin: $0.500 per million tokens blended against $6.60, roughly 13.2× less. A single 100K-input, 10K-output job costs $0.032 on GPT-5.6 Luna against $0.450 on Grok 3. Blended cost weights input at 70% and output at 30%; price your own token split for an exact answer, since the cheaper model on a blended basis is not always cheaper for your workload.
Which performs better, GPT-5.6 Luna or Grok 3?
GPT-5.6 Luna leads on 2 of the 2 benchmarks both models report. The widest gap is on LMArena Elo, where GPT-5.6 Luna leads by 119 points. These are the figures each provider or public leaderboard publishes, not results we re-run, and a benchmark average can hide the specific behaviour your workload depends on.
Which has the larger context window, GPT-5.6 Luna or Grok 3?
GPT-5.6 Luna takes a 1,050,000-token context window against 131,000, giving 8.0× more room for long documents or whole-codebase work. The context window caps everything in a single request: prompt, retrieved documents, conversation history and the model’s own output all share it.
Can I compare GPT-5.6 Luna and Grok 3 on my own numbers?
Yes. Open both in the side-by-side comparison tool to see every field at once, or use the token calculator to price your actual prompt and monthly request volume against each model. Both are free and need no sign-up.
Price it for your own workload
Related matchups
Terms used on this page
Prices and scores are recomputed on every deploy from the catalogue. Prices checked 12 August 2026.