Gemini 3.5 Flash vs GPT-5.1-Codex
A side-by-side comparison of two multimodal models — real specs, pricing, strengths and weaknesses, and a clear verdict on which to choose. Kept current by our agents.
Quick verdict: which should you choose?
Choose Gemini 3.5 Flash if you need
- ✓higher intelligence (45.4 index) and versatile multimodal handling of text, image, video, and audio
- ✓largest context window (1,048,576 tokens) for processing extensive inputs
- ✓lower price at $9 per million tokens with strong speed-efficiency balance
- ✓broad data-type versatility without being limited to text and image only
Choose GPT-5.1-Codex if you need
- ✓maximum output speed (189.63 t/s) for high-throughput text and image generation
- ✓specialized strength in extended coding workflows with visual context integration
- ✓coherent handling of very large inputs specifically for software development
- ✓targeted performance on coding tasks where prompt engineering is acceptable
Verdict
Gemini 3.5 Flash leads with a higher intelligence index (45.4 vs 34.7), much larger context (1M+ vs 400k tokens), lower price, and broader multimodal support across video and audio. GPT-5.1-Codex wins on raw output speed (189.63 vs 160.31 t/s) and specialized coding workflows that integrate visual context. Overall, Gemini offers stronger general multimodal performance while GPT-5.1-Codex targets extended software development tasks.
Gemini 3.5 Flash vs GPT-5.1-Codex: side by side
| Spec | Gemini 3.5 Flash | GPT-5.1-Codex | Winner |
|---|---|---|---|
| Intelligence | 45.4 | 34.7 | Gemini 3.5 Flash |
| Output speed | 160 t/s | 190 t/s | GPT-5.1-Codex |
| Output price | $9.00/1M | $10.00/1M | Gemini 3.5 Flash |
| Context | 1049K | 400K | Gemini 3.5 Flash |
| Params | — | — | Tie |
| Provider | OpenAI | Tie |
Detailed analysis
Intelligence
Winner: Gemini 3.5 FlashGemini 3.5 Flash scores 45.4 on the intelligence index compared to GPT-5.1-Codex at 34.7. This gap indicates stronger general reasoning and multimodal task performance for Gemini. GPT-5.1-Codex instead emphasizes domain-specific coding strengths.
Speed
Winner: GPT-5.1-CodexGPT-5.1-Codex delivers 189.63 tokens per second versus Gemini 3.5 Flash at 160.31 t/s. The speed advantage favors GPT for high-volume text and image output. Gemini trades some speed for broader multimodal efficiency.
Context & Pricing
Winner: Gemini 3.5 FlashGemini 3.5 Flash provides a 1,048,576-token context at $9 per million tokens while GPT-5.1-Codex offers 400,000 tokens at $10 per million. The larger window and lower cost give Gemini clear advantages for long multimodal inputs. GPT notes higher cost at maximum context usage.
Multimodal Scope
Winner: Gemini 3.5 FlashGemini 3.5 Flash supports text, image, video, and audio inputs with strong integration. GPT-5.1-Codex is limited to text and image only. This makes Gemini the more versatile multimodal option per the stated capabilities.
Gemini 3.5 Flash
Pros
- +High speed and efficiency
- +Strong multimodal integration
- +Large context window support
Cons
- –Trades depth for speed on complex tasks
- –Variable performance on specialized domains
- –Context utilization depends on task
GPT-5.1-Codex
Pros
- +Strong performance on extended coding workflows
- +Effective integration of visual context with code
- +Handles very large inputs without losing coherence
Cons
- –Limited to text and image inputs only
- –High computational cost for maximum context
- –May require careful prompt engineering for complex tasks
Summary: Gemini 3.5 Flash vs GPT-5.1-Codex
Choose Gemini 3.5 Flash for most multimodal workloads needing higher intelligence, larger context, lower cost, and video/audio support. Select GPT-5.1-Codex when maximum speed and coding-specific workflows with visual context are the priority. The facts show Gemini winning on breadth and value while GPT leads narrowly on speed and specialization.
Frequently asked questions
Gemini 3.5 Flash is better overall due to its higher intelligence index, larger context, lower price, and support for video and audio in addition to text and image.