Gemini 3.5 Flash vs GPT-5.6 Terra
Which one to choose
Pick Gemini 3.5 Flash for routine, high-throughput chat, extraction and summarization where speed and steady behavior matter more than depth; pick GPT-5.6 Terra for everyday coding and writing that benefit from adjustable reasoning. Terra is the more capable of the two on analytical turns, but OpenAI now marks the GPT-5.6 family as legacy, and Google has newer Flash models than 3.5.
Pricing comparison
| Gemini 3.5 Flash | GPT-5.6 Terra | |
|---|---|---|
| Model maker | OpenAI | |
| Delivery availability | Available | Available |
| Context window | 1M | 1.05M |
| Max output | 64K | 128K |
| Official price | Input$1.50per 1M tokensOutput$9.00per 1M tokens | Input$2.00per 1M tokensOutput$12.00per 1M tokens |
| TokenLab price | Input$0.75per 1M tokensOutput$4.50per 1M tokens | Input$0.60per 1M tokensOutput$3.60per 1M tokens |
| Model performance |
|
|
| Capabilities | JSON modePrompt CacheTool useVision | CodeJSON modePrompt CacheReasoningTool useVision |
Choose Gemini 3.5 Flash when
- You run volume pipelines of extraction, summarization or screenshot reading.
- You want a stable Flash model as a baseline before testing newer Gemini Flash releases.
- Your assistant carries a task through a few tool-calling steps rather than a long agent run.
Choose GPT-5.6 Terra when
- One deployment must cover quick replies and slower analytical turns through adjustable reasoning.
- You do everyday coding and writing and want a mid-tier model rather than the flagship.
- You are replacing GPT-5.5 on routine workloads and want a model OpenAI positions as competitive with it.
How they differ
| Aspect | Gemini 3.5 Flash | GPT-5.6 Terra |
|---|---|---|
| Tier | Baseline Flash for routine, high-throughput work, below the 3.6, 3.7 and 3.8 Flash releases. | Middle model of GPT-5.6, between Luna and the Sol flagship. |
| Reasoning | Not marked as a thinking model, so hard multi-step reasoning is better sent elsewhere. | Reasoning is adjustable per request. |
| Coding and agents | The later Flash models are stronger on coding and agent tasks. | Covers most coding and writing jobs; Sol remains the choice for the hardest agent runs. |
| Lifecycle | Stable model, with newer Flash versions available. | The GPT-5.6 family is listed as legacy; new projects are pointed to GPT-6. |
| Inputs and outputs | Text and image input, schema-bound JSON, context caching. | Text and image input, structured JSON, tool calls. |
Summary
- Gemini 3.5 Flash: Input $0.75 / Output $4.50 per 1M tokens; GPT-5.6 Terra: Input $0.60 / Output $3.60 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.
- GPT-5.6 Terra supports 2.0x more output tokens
FAQ
Which is better, Gemini 3.5 Flash or GPT-5.6 Terra?
Terra is the stronger choice when a task needs reasoning, because its effort is adjustable. Gemini 3.5 Flash is the steadier fit for routine volume work. They sit in different tiers, so match the model to the job.
Should I start a new project on either?
Probably neither. Google has Flash models newer than 3.5 that do better on coding and agents, and OpenAI lists GPT-5.6 as legacy and points to GPT-6. Both remain fine for existing workloads.
Can Terra replace Gemini 3.5 Flash without prompt changes?
For plain chat, extraction and summarization, prompts usually carry over. Adjust anything that relies on Gemini-specific request fields, and decide what reasoning effort to set on Terra, then re-run your evaluation set.
Do they both read images?
Yes, both take images with text and call tools. Both also return structured JSON, so the same screenshot-to-JSON pipeline can be tested on each before you commit to one.
Which is cheaper, Gemini 3.5 Flash or GPT-5.6 Terra?
Gemini 3.5 Flash: Input $0.75 / Output $4.50 per 1M tokens; GPT-5.6 Terra: Input $0.60 / Output $3.60 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 3.5 Flash and GPT-5.6 Terra?
GPT-5.6 Terra: Code, Reasoning
Sources
Reviewed Oct 2, 2026