GPT-5 Pro vs Gemini 3.1 Flash-Lite
Detailed pricing comparison and cost analysis.
Updated September 2026
Cost Simulator
| Feature | GPT-5 Pro | Gemini 3.1 Flash-Lite |
|---|---|---|
| Provider | OpenAI | |
| Input Price (1M) | $15.00 | $0.25 |
| Output Price (1M) | $120.00 | $1.50 |
| Context Window | 400,000 | 1,000,000 |
Verdict
GPT-5 Pro costs $15.00 per 1M input tokens and $120.00 per 1M output tokens. Gemini 3.1 Flash-Lite costs $0.25 per 1M input tokens and $1.50 per 1M output tokens. Gemini 3.1 Flash-Lite is 98% cheaper on input tokens than GPT-5 Pro. For output tokens, Gemini 3.1 Flash-Lite is the more affordable option at $1.50/1M vs $120.00.
On context window, Gemini 3.1 Flash-Lite supports 1,000,000 tokens — meaning it can fit more conversation history, documents, or code in a single request. This matters for RAG pipelines, long document analysis, and agentic workflows where context builds up over many turns.
When to choose GPT-5 Pro
- ✓ You are already integrated with OpenAI
When to choose Gemini 3.1 Flash-Lite
- ✓ You need the lowest input token cost ($ 0.25/1M)
- ✓ Your workload is output-heavy — Gemini 3.1 Flash-Lite generates text cheaper
- ✓ You need a larger context window (1,000,000 tokens)
- ✓ You are already integrated with Google
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 GPT-5 Pro cheaper than Gemini 3.1 Flash-Lite? ▼
Gemini 3.1 Flash-Lite is cheaper on input tokens at $0.25/1M vs $15.00/1M for GPT-5 Pro — a 98% saving.
What is the context window of GPT-5 Pro vs Gemini 3.1 Flash-Lite? ▼
GPT-5 Pro has a 400,000-token context window. Gemini 3.1 Flash-Lite has a 1,000,000-token context window. Gemini 3.1 Flash-Lite supports the larger context, suitable for longer documents and agentic workflows.
Which model is better: GPT-5 Pro or Gemini 3.1 Flash-Lite? ▼
The best choice depends on your use case. For cost efficiency on input tokens, Gemini 3.1 Flash-Lite is the cheaper option. For maximum context length, Gemini 3.1 Flash-Lite supports 1,000,000 tokens. Use the comparison table above to find the right fit for your workload.