Question 1

What does this GPT-5.1 Chat vs GPT-5 Nano 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: GPT-5.1 Chat or GPT-5 Nano?

Accepted Answer

GPT-5.1 Chat lists $1.25 input and $10.00 output per 1M tokens. GPT-5 Nano lists $0.05 input and $0.40 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: GPT-5.1 Chat or GPT-5 Nano?

Accepted Answer

GPT-5.1 Chat lists 128K tokens and GPT-5 Nano lists 400K. GPT-5 Nano therefore has the larger recorded context window, but capacity alone is not a quality score.

Question 4

Which is faster: GPT-5.1 Chat or GPT-5 Nano?

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 GPT-5.1 Chat and GPT-5 Nano support?

Accepted Answer

GPT-5.1 Chat records text, image input and text output. GPT-5 Nano 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 GPT-5.1 Chat or GPT-5 Nano?

Accepted Answer

Consider GPT-5 Nano if you need larger context or larger maximum output or a lower listed input rate or a lower listed output 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	GPT-5.1 Chat	GPT-5 Nano
Provider	OpenAI	OpenAI
Listed pricing route	OpenAI	OpenAI
Model family	gpt-codex	gpt-nano
Accepted inputs	text, image	text, image
Produced outputs	text	text
Context window	128K	400KHigher
Max output	16.38K	128KHigher
Input price / 1M	$1.25	$0.05Lower
Output price / 1M	$10.00	$0.40Lower
Reasoning mode	Documented	Documented
Tool calling	Documented	Documented
Image input	Documented	Documented
Audio input	Not documented	Not documented
Structured output	Documented	Documented
License	Proprietary	Proprietary

GPT-5.1 Chat vs GPT-5 Nano

GPT-5.1 Chat

GPT-5 Nano

Key differences

Pricing, limits and capabilities

Which model should you choose?

Documentation and model profiles

Questions people ask

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