Question 1

What does this Gemini 3.5 Flash vs GPT-5.1 Chat comparison cover?

Accepted Answer

It brings together documented inputs and outputs, token limits, deployment terms and available pricing. When both models have source-linked, verified results on a shared benchmark, those results are shown with their individual sources. The comparison is a starting point for evaluating your own workload.

Question 2

Which is cheaper: Gemini 3.5 Flash or GPT-5.1 Chat?

Accepted Answer

Gemini 3.5 Flash lists $1.50 input and $9.00 output per 1M tokens. GPT-5.1 Chat lists $1.25 input and $10.00 output. The cheaper workload depends on the mix of input and output. Long-context tiers, caching, batch processing and retries can change the bill.

Question 3

Which has the larger context window: Gemini 3.5 Flash or GPT-5.1 Chat?

Accepted Answer

Gemini 3.5 Flash lists 1.05M tokens and GPT-5.1 Chat lists 128K. Gemini 3.5 Flash therefore has the larger recorded context window, but capacity alone is not a quality score.

Question 4

Which is faster: Gemini 3.5 Flash or GPT-5.1 Chat?

Accepted Answer

There is no matched speed measurement for both models with the same source, host, region and date. Test the same prompts at your expected concurrency and measure time to the first useful response as well as complete task time.

Question 5

What input and output types do Gemini 3.5 Flash and GPT-5.1 Chat support?

Accepted Answer

Gemini 3.5 Flash records text, image, video, audio, pdf input and text output. GPT-5.1 Chat records text, image input and text output. “Not documented” means the current source record is incomplete; it does not prove that a modality is unsupported.

Question 6

Should I choose Gemini 3.5 Flash or GPT-5.1 Chat?

Accepted Answer

Consider Gemini 3.5 Flash if you need larger context or larger maximum output or a lower listed output rate. Consider GPT-5.1 Chat if you need a lower listed input rate. Test both on the same representative examples and judge the output against your acceptance criteria. Include tool failures, retries and the time to a completed task.

Specification	Gemini 3.5 Flash	GPT-5.1 Chat
Provider	Google	OpenAI
Listed pricing route	Google	OpenAI
Model family	gemini-flash	gpt-codex
Accepted inputs	text, image, video, audio, pdf	text, image
Produced outputs	text	text
Context window	1.05MHigher	128K
Max output	65.54KHigher	16.38K
Input price / 1M	$1.50	$1.25Lower
Output price / 1M	$9.00Lower	$10.00
Reasoning mode	Documented	Documented
Tool calling	Documented	Documented
Image input	Documented	Documented
Audio input	Documented	Not documented
Structured output	Documented	Documented
License	Proprietary	Proprietary

Gemini 3.5 Flash vs GPT-5.1 Chat

Gemini 3.5 Flash

GPT-5.1 Chat

Key differences

Pricing, limits and capabilities

Which model should you choose?

Documentation and model profiles

Questions people ask

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