Side-by-side comparison of pricing, 12 benchmarks, and generation speed.
| Metric | Solar Pro 4 | GPT-5.6 Luna (low) |
|---|---|---|
| Input ($/M tokens) | $0.3 | $0.2 |
| Output ($/M tokens) | $1.2 | $1.2 |
Verdict. Solar Pro 4 wins the overall benchmark matchup 2–0 across 2 overlapping categories, but raw benchmark score is only one input to the decision.
Pricing. Both models sit in the budget bracket for output-token pricing. At 1.0× the per-million-token cost, GPT-5.6 Luna (low) is meaningfully cheaper if your traffic is output-heavy (long completions, document generation, agent loops). GPT-5.6 Luna (low) makes more sense when output volume is low and absolute reasoning quality justifies the premium.
Strengths. Solar Pro 4 is strongest on Coding Index (52.7), Intelligence Index (41.6). GPT-5.6 Luna (low) leads on Coding Index (44.2), Intelligence Index (33.9).
Speed. On throughput, GPT-5.6 Luna (low) generates tokens at 109 tok/s versus 78 tok/s — about 28% faster. On time-to-first-token, GPT-5.6 Luna (low) responds in 1730ms vs 1950ms, which matters most for chat-style UIs.
Provider. Upstage and OpenAI sell to overlapping but distinct developer audiences: Upstage tends to ship frontier reasoning models with premium positioning, while OpenAI often prices more aggressively. Your existing vendor relationships, billing, and SLA preferences may matter as much as the raw numbers above.
Workload cost. Workload scenarios (per million requests at 30M input + 15M output tokens): Solar Pro 4 costs $27.00 ($324/year); GPT-5.6 Luna (low) costs $24.00 ($288/year). At a smaller 5M-input/2M-output scale (single-developer tool or prototype): Solar Pro 4 ≈ $3.90/run, GPT-5.6 Luna (low) ≈ $3.40/run. At agent/realtime scale (200M input / 100M output per million requests): Solar Pro 4 ≈ $180/run, GPT-5.6 Luna (low) ≈ $160/run. GPT-5.6 Luna (low) becomes more attractive at higher volume — the absolute per-token pricing difference compounds when you ship at scale.
Recommendation. Both models have legitimate use cases — the right answer depends on whether you are optimizing for benchmark ceiling, latency, or unit cost. Start with the cheaper / faster model, evaluate against your specific task, and only switch if the upgrade shows a meaningful lift.
Data from Artificial Analysis API — 12 benchmarks
GPT-5.6 Luna (low) is cheaper overall. Its blended price (3:1 input/output ratio) is $0.45/M tokens vs $0.53/M for Solar Pro 4.
Solar Pro 4 wins 2 out of 12 benchmarks compared to 0 for GPT-5.6 Luna (low). See the detailed benchmark chart above for per-category results.
GPT-5.6 Luna (low) generates tokens faster at 109 tok/s vs 78 tok/s. However, GPT-5.6 Luna (low) has lower time-to-first-token (1.73s vs 1.95s).
Choose based on your priorities: GPT-5.6 Luna (low) for lower cost, Solar Pro 4 for stronger benchmark performance, and GPT-5.6 Luna (low) for faster generation. For latency-sensitive apps, check the TTFT comparison above.