Google Gemini vs OpenAI GPT: monthly cost for a 10k-user chatbot from current list prices.
Bottom line: cheapest is OpenAI: GPT-6 Luna Pro at about $53.87/month; the median model costs $897.75; the most expensive, OpenAI: GPT-6 Astra Pro, costs $5,386. 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 2026-10-15 ✔ matches |
| OpenAI | OpenAI: GPT-6 Luna | $0.1 | $0.5 | $53.87 | source 2026-10-15 ✔ matches |
| Google: Gemini 3.1 Flash Lite | $0.25 | $1.5 | $149.62 | source 2026-10-15 ✔ matches | |
| Google: Gemini 3.5 Flash Lite | $0.3 | $2.5 | $221.44 | source 2026-10-15 ✔ matches | |
| Google: Gemini 3.7 Flash | $0.75 | $3.75 | $403.99 | source 2026-10-15 ✔ matches | |
| Google: Gemini 3.6 Flash | $0.75 | $3.75 | $403.99 | source 2026-10-15 ✔ matches | |
| Google: Gemini 3.8 Flash | $0.825 | $4.125 | $444.39 | source 2026-10-15 ⚠ differs from lab price ($0.75/$3.75) | |
| Google: Nano Banana 2.1 | $1.5 | $7.5 | $807.98 | source 2026-10-15 no 2nd source | |
| Google: Gemini 3.5 Flash | $1.5 | $9.0 | $897.75 | source 2026-10-15 ✔ matches | |
| Google: Gemini 4 Argon | $2.0 | $10.0 | $1,077 | source 2026-10-15 no 2nd source | |
| OpenAI | OpenAI: GPT-6.1 Sol Pro | $2.0 | $10.0 | $1,077 | source 2026-10-15 ✔ matches |
| OpenAI | OpenAI: GPT-6.1 Sol | $2.0 | $10.0 | $1,077 | source 2026-10-15 ✔ matches |
| OpenAI | OpenAI: GPT-6 Sol Pro | $2.0 | $10.0 | $1,077 | source 2026-10-15 ✔ matches |
| OpenAI | OpenAI: GPT-6 Sol | $2.0 | $10.0 | $1,077 | source 2026-10-15 ✔ matches |
| OpenAI | OpenAI: GPT-6 Astra | $10.0 | $50.0 | $5,386 | source 2026-10-15 ✔ matches |
| OpenAI | OpenAI: GPT-6 Astra Pro | $10.0 | $50.0 | $5,386 | source 2026-10-15 ✔ matches |
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