Gemini 3.8 Flash vs GPT-5.4 mini
Which one to choose
Pick Gemini 3.8 Flash for long-horizon software engineering and autonomous agents that need thinking, schema-bound JSON and the newest Flash model Google recommends for new projects; pick GPT-5.4 mini for coding subagents and computer use inside a larger-model-plans, small-models-execute setup. Gemini 3.8 Flash is the heavier thinker of the two, while GPT-5.4 mini is built to be a fast worker.
Pricing comparison
| Gemini 3.8 Flash | GPT-5.4 mini | |
|---|---|---|
| Model maker | OpenAI | |
| Delivery availability | Available | Available |
| Context window | 1M | 400K |
| Max output | 64K | 128K |
| Official price | Input$0.75per 1M tokensOutput$3.75per 1M tokens | Input$0.75per 1M tokensOutput$4.50per 1M tokens |
| TokenLab price | Input$0.375per 1M tokensOutput$1.88per 1M tokens | Input$0.525per 1M tokensOutput$3.15per 1M tokens |
| Model performance |
|
|
| Capabilities | JSON modePrompt CacheTool useVision | Prompt CacheTool useVision |
Choose Gemini 3.8 Flash when
- Your agent works through many steps and must not lose the thread on a large software task.
- You need schema-bound JSON output in the same call that reasons and uses tools.
- You are starting a new project and want Google's recommended current Flash model.
Choose GPT-5.4 mini when
- A larger model plans and you need small models to run focused tasks in parallel.
- Your workflow uses computer use or MCP.
- You want reasoning effort to default to none for speed and raise it only on certain calls.
How they differ
| Aspect | Gemini 3.8 Flash | GPT-5.4 mini |
|---|---|---|
| Design goal | Google's most intelligent Flash model, for long-horizon engineering and enterprise workflows. | OpenAI's strongest small model, a faster version of GPT-5.4 behavior for subagent roles. |
| Reasoning | Thinking is supported for planning and debugging before the model acts. | Reasoning effort runs from none to xhigh and defaults to none, favoring speed. |
| Structured output | Supports schema-bound JSON output. | Does not offer response-schema enforcement; validate JSON in your own code. |
| Computer use and MCP | Tool calling covers agents with many integrations. | Computer use and MCP are supported. |
| Escalation path | Gemini 3.1 Pro may still win on tasks that reward Pro-tier reasoning. | Complex or ambiguous planning is better left to GPT-5.4 or a Pro tier. |
Summary
- Gemini 3.8 Flash: Input $0.375 / Output $1.88 per 1M tokens; GPT-5.4 mini: Input $0.525 / Output $3.15 per 1M tokens. Rates depend on the billing unit, specification, and usage. Compare matching conditions in the model's detailed pricing; a single rate does not determine the total cost.
- Gemini 3.8 Flash has a 2.6x larger context window
- GPT-5.4 mini supports 2.0x more output tokens
FAQ
Which is better for coding agents, Gemini 3.8 Flash or GPT-5.4 mini?
For one agent carrying a long software task through many steps, Gemini 3.8 Flash is the closer fit. For a subagent that executes a narrow job under a larger planner, GPT-5.4 mini is. Test both on the role you actually give them.
Does either guarantee JSON that matches a schema?
Gemini 3.8 Flash supports schema-bound JSON output. GPT-5.4 mini does not offer response-schema enforcement, so parse and validate its JSON in your own code before using it downstream.
Can I replace GPT-5.4 mini with Gemini 3.8 Flash?
Plain chat and tool prompts usually carry over, but check any use of reasoning effort values, computer use or MCP, which belong to GPT-5.4 mini. Re-run your evaluation set after the change.
Do they both handle images?
Both accept images with text. GPT-5.4 mini returns text only, and Gemini 3.8 Flash is also described as returning text and JSON, so neither is an image-generation choice.
Which is cheaper, Gemini 3.8 Flash or GPT-5.4 mini?
Gemini 3.8 Flash: Input $0.375 / Output $1.88 per 1M tokens; GPT-5.4 mini: Input $0.525 / Output $3.15 per 1M tokens. Rates depend on the billing unit, specification, and usage. Compare matching conditions in the model's detailed pricing; a single rate does not determine the total cost.
What are the key differences between Gemini 3.8 Flash and GPT-5.4 mini?
Gemini 3.8 Flash: JSON mode
Sources
Reviewed Oct 2, 2026