OpenAI API cost by model for a 10k-user chatbot, from live list prices, with a calculator for your own numbers.
Bottom line: cheapest is OpenAI: GPT-6 Luna Pro at about $53.87/month; the median model costs $1,077/month; the most expensive, OpenAI: GPT-6 Astra Pro, costs $5,386/month. That is a 100× spread for the same workload.
Scenario: 10,000 monthly users × 30 messages, 600 words in / 150 words out per message.
| Vendor | Model | In $/1M | Out $/1M | Est. monthly cost | Source / check |
|---|---|---|---|---|---|
| OpenAI | OpenAI: GPT-6 Luna Pro | $0.1 | $0.5 | $53.87 | source 2026-10-16 ✔ matches |
| OpenAI | OpenAI: GPT-6 Luna | $0.1 | $0.5 | $53.87 | source 2026-10-16 ✔ matches |
| OpenAI | OpenAI: GPT-6.1 Sol Pro | $2.0 | $10.0 | $1,077 | source 2026-10-16 ✔ matches |
| OpenAI | OpenAI: GPT-6.1 Sol | $2.0 | $10.0 | $1,077 | source 2026-10-16 ✔ matches |
| OpenAI | OpenAI: GPT-6 Sol Pro | $2.0 | $10.0 | $1,077 | source 2026-10-16 ✔ matches |
| OpenAI | OpenAI: GPT-6 Sol | $2.0 | $10.0 | $1,077 | source 2026-10-16 ✔ matches |
| OpenAI | OpenAI: GPT-6 Astra | $10.0 | $50.0 | $5,386 | source 2026-10-16 ✔ matches |
| OpenAI | OpenAI: GPT-6 Astra Pro | $10.0 | $50.0 | $5,386 | source 2026-10-16 ✔ matches |
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Prices from OpenRouter's public API, cross-checked with InferIndex. No spam.