Gemini 3.1 Pro is 2.5x cheaper on input and 2.5x cheaper on output. That's a massive price difference for models that both claim flagship-level performance.
Head-to-Head Comparison
| Feature | GPT-5.5 | Gemini 3.1 Pro |
|---|---|---|
| Input Price | $5.00 / 1M | $2.00 / 1M |
| Output Price | $30.00 / 1M | $12.00 / 1M |
| Context Window | 1M tokens | 1M tokens |
| Reasoning | Excellent | Excellent |
| Code Generation | Best-in-class | Very strong |
| Multimodal | Text + Vision | Text + Vision + Audio + Video |
| Speed (TTFT) | ~1.5s | ~0.8s |
| Safety | Strong guardrails | Moderate guardrails |
| Ecosystem | Larger (plugins, assistants) | Growing (Vertex AI) |
Real-World Cost Comparison
Let's model four common use cases to see how the price difference plays out at scale.
| Use Case | GPT-5.5 Cost | Gemini 3.1 Pro Cost | Savings |
|---|---|---|---|
| Chatbot (1K req/day, 500 in / 1K out) | $525/mo | $210/mo | 60% |
| Code Assistant (500 req/day, 3K in / 2K out) | $1,275/mo | $510/mo | 60% |
| Doc Analysis (200 req/day, 50K in / 2K out) | $2,100/mo | $840/mo | 60% |
| High Volume (10K req/day, 200 in / 100 out) | $3,900/mo | $1,560/mo | 60% |
The savings are consistent: Gemini 3.1 Pro costs 60% less across every use case. The price ratio is fixed at 2.5x, so the savings percentage holds regardless of workload.
When to Choose GPT-5.5
GPT-5.5 is worth the premium if:
- Code generation is your primary use case — GPT-5.5 still leads in complex multi-file code generation and debugging
- You need the largest ecosystem — OpenAI's plugins, assistants API, and third-party integrations are more mature
- Safety is paramount — GPT-5.5 has stronger guardrails for sensitive applications
- You're building for enterprise — OpenAI's enterprise agreements and compliance certifications are more established
When to Choose Gemini 3.1 Pro
Gemini 3.1 Pro is the better choice if:
- Cost matters — 60% savings is hard to ignore, especially at scale
- You need massive context — 1M tokens vs 1M. Process entire codebases or 2,000-page documents in one call
- Multimodal is important — Native audio and video processing, not just text and images
- Speed is critical — 2x faster time-to-first-token for real-time applications
- You're on Google Cloud — Seamless integration with Vertex AI, BigQuery, and GCP infrastructure
The Verdict
For most developers, Gemini 3.1 Pro is the better value. It delivers 90% of GPT-5.5's capability at 40% of the price, with a larger context window and faster speeds.
Choose GPT-5.5 if you need absolute best-in-class code generation, have enterprise compliance requirements, or are deeply invested in the OpenAI ecosystem. But for pure cost-per-performance, Gemini 3.1 Pro wins this round.
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