chat_openai: Chat with an OpenAI model

In ellmer: Chat with Large Language Models

Chat with an OpenAI model

Description

This is the main interface to OpenAI's models, using the responses API. You can use this to access OpenAI's latest models and features like image generation and web search. If you need to use an OpenAI-compatible API from another provider, or the chat completions API with OpenAI,use chat_openai_compatible() instead.

Note that a ChatGPT Plus membership does not grant access to the API. You will need to sign up for a developer account (and pay for it) at the developer platform.

Usage

chat_openai(
  system_prompt = NULL,
  base_url = "https://api.openai.com/v1",
  api_key = NULL,
  credentials = NULL,
  model = NULL,
  params = NULL,
  api_args = list(),
  api_headers = character(),
  service_tier = c("auto", "default", "flex", "priority"),
  echo = c("none", "output", "all")
)

models_openai(
  base_url = "https://api.openai.com/v1",
  api_key = NULL,
  credentials = NULL
)

Arguments

system_prompt	A system prompt to set the behavior of the assistant.
base_url	The base URL to the API endpoint.
api_key	Use credentials instead.
credentials	Override the default credentials. You generally should not need this argument; instead set the OPENAI_API_KEY environment variable. The best place to set this is in .Renviron, which you can easily edit by calling usethis::edit_r_environ(). If you do need additional control, this argument takes a zero-argument function that returns either a string (the API key), or a named list (added as additional headers to every request).
model	The model to use for the chat (defaults to "gpt-5.4"). We regularly update the default, so we strongly recommend explicitly specifying a model for anything other than casual use. Use models_openai() to see all options.
params	Common model parameters, usually created by params().
api_args	Named list of arbitrary extra arguments appended to the body of every chat API call. Combined with the body object generated by ellmer with modifyList().
api_headers	Named character vector of arbitrary extra headers appended to every chat API call.
service_tier	Request a specific service tier. There are four options: "auto" (default): uses the service tier configured in Project settings. "default": standard pricing and performance. "flex": slower and cheaper. "priority": faster and more expensive.
echo	One of the following options: none: don't emit any output (default when running in a function). output: echo text and tool-calling output as it streams in (default when running at the console). all: echo all input and output. Note this only affects the chat() method.

Value

A Chat object.

See Also

Other chatbots: chat_anthropic(), chat_aws_bedrock(), chat_azure_openai(), chat_cloudflare(), chat_databricks(), chat_deepseek(), chat_github(), chat_google_gemini(), chat_groq(), chat_huggingface(), chat_lmstudio(), chat_mistral(), chat_ollama(), chat_openai_compatible(), chat_openrouter(), chat_perplexity(), chat_portkey(), chat_posit()

Examples

chat <- chat_openai()
chat$chat("
  What is the difference between a tibble and a data frame?
  Answer with a bulleted list
")

chat$chat("Tell me three funny jokes about statisticians")

ellmer documentation built on July 14, 2026, 1:07 a.m.