What is GPT-5.1 Chat?

GPT-5.1 Chat is a variant of GPT-5.1 specifically tuned for ChatGPT conversations, employing light adaptive reasoning for complex queries.

How is GPT-5.1 Chat different from GPT-5.1?

GPT-5.1 Chat mirrors ChatGPT behavior more closely, while standard GPT-5.1 is recommended for most API applications.

When should I use GPT-5.1 Chat?

Use it for chat-specific scenarios, testing ChatGPT enhancements via API, and low-latency conversational chatbots.

How much does GPT-5.1 Chat cost?

GPT-5.1 Chat pricing is $1.25 per 1M input tokens and $10.00 per 1M output tokens. Cached input tokens cost $0.125 per 1M.

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GPT-5.1 Chat

GPT-5.1 conversational model used in ChatGPT.

Try in Playground

Community Sentiment

Mixed

Based on Reddit reviews

Community Verdict

Best for Chat APIs

Based on Reddit reviews

Input Modalities

Text, Images

Output Modalities

Text

Price / 1M tokens

$1.25$10

InputOutput

Best For

Chat-style APIs mimicking ChatGPT

Testing latest ChatGPT features via API

Low-latency bots (Instant mode)

128k context, 16k output limit

Light reasoning scenarios

Avoid For

General API use (gpt-5.1 recommended)

Conditional tool use (regressions)

Complex tool chains (unreliable)

Deep reasoning (use Thinking mode)

Tasks needing precise tool logic

128,000 context window

16,000 max output tokens

Jan 1, 2024 knowledge cutoff

Reasoning supported

Parameters

While OpenAI documents a unified parameter set for the Chat Completions and Responses APIs, each model supports only a limited subset of model-specific parameters and values. This table lists the supported model-specific GPT-5.1 Chat API parameters and allowed values.

Parameter	Description	Path	Supported Values
Model	Selects the model version for the request	model	gpt-5.1-chatgpt-5.1-chat-latest
Message roles	Defines the role of the message in the input	messages[].role	developersystemuserassistant
Reasoning effort	Controls the depth of internal reasoning used by the model	reasoning_effort	medium
Reasoning summary	Controls whether the model produces a concise or detailed reasoning summary	reasoning_summary	detailedconciseautonull
Max output tokens	Max output tokens the model may generate	max_completion_tokens	16 .. 16,000
Verbosity	Controls how brief or detailed the generated response is	verbosity	medium
Output format	Specifies the output format, including structured JSON schemas	response_format	textjson_objectjson_schema
Temperature	Controls how random or deterministic the output is	temperature	Not supported
Top P	Controls how diverse the output tokens are	top_p	Not supported
Presence penalty	Encourages the model to introduce new topics	presence_penalty	Not supported
Frequency penalty	Reduces repetition of the same words or phrases	frequency_penalty	Not supported

Pricing

GPT-5.1 Chat API pricing is based on token usage for input and output. Prices are listed per 1M tokens, with lower rates for cached input. Tool-specific features may add per-call fees.

Text tokens

Per 1M tokens

Input$1.25

Cached input$0.13

Output$10.00

Example costs (GPT-5.1 Chat)

TASK

APPROX COST

Chat conversation (1k tokens)

~$0.001

Long chat session (10k tokens)

~$0.01

Multi-turn conversation (50k tokens)

~$0.06

Modalities

What the model can accept and produce

TextInput and output

ImagesInput only

AudioNot supported

VideoNot supported

Features

Platform-level capabilities

StreamingSupported

Function callingSupported

Structured outputsSupported

Fine-tuningNot supported

DistillationNot supported

Predicted outputsNot supported

Tools

Tools supported by this model when using the Responses API.

Web searchSupported

File searchSupported

Image generationSupported

Code interpreterSupported

MCPSupported

Computer useNot supported

Snapshots

GPT-5.1 Chat model snapshots ensure stable behavior by locking a specific version. See all available snapshots and aliases below.

gpt-5.1-chat-latest

↪ gpt-5.1-chat-latest

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