Fine-tuning

Create fine-tuning job

Changed on Oct 26, 2026

Creates a fine-tuning job which begins the process of creating a new model from a given dataset.

Response includes details of the enqueued job including job status and the name of the fine-tuned models once complete.

Learn more about fine-tuning

post/fine_tuning/jobs

Request

Base URL
https://api.openai.com/v1
URL
https://api.openai.com/v1/fine_tuning/jobs
Auth
HTTP bearer

Request body

training_filestring required

The ID of an uploaded file that contains training data.

See upload file for how to upload a file.

Your dataset must be formatted as a JSONL file. Additionally, you must upload your file with the purpose fine-tune.

The contents of the file should differ depending on if the model uses the chat, completions format, or if the fine-tuning method uses the preference format.

See the fine-tuning guide for more details.

suffixstring nullable

A string of up to 64 characters that will be added to your fine-tuned model name.

For example, a suffix of "custom-model-name" would produce a model name like ft:gpt-4o-mini:openai:custom-model-name:7p4lURel.

validation_filestring nullable

The ID of an uploaded file that contains validation data.

If you provide this file, the data is used to generate validation metrics periodically during fine-tuning. These metrics can be viewed in the fine-tuning results file. The same data should not be present in both train and validation files.

Your dataset must be formatted as a JSONL file. You must upload your file with the purpose fine-tune.

See the fine-tuning guide for more details.

seedinteger nullable

The seed controls the reproducibility of the job. Passing in the same seed and job parameters should produce the same results, but may differ in rare cases. If a seed is not specified, one will be generated for you.

metadataMetadata nullable

Set of 16 key-value pairs that can be attached to an object. This can be useful for storing additional information about the object in a structured format, and querying for objects via API or the dashboard.

Keys are strings with a maximum length of 64 characters. Values are strings with a maximum length of 512 characters.

Response

idstring required

The object identifier, which can be referenced in the API endpoints.

created_atinteger required

The Unix timestamp (in seconds) for when the fine-tuning job was created.

fine_tuned_modelstring nullable required

The name of the fine-tuned model that is being created. The value will be null if the fine-tuning job is still running.

finished_atinteger nullable required

The Unix timestamp (in seconds) for when the fine-tuning job was finished. The value will be null if the fine-tuning job is still running.

modelstring required

The base model that is being fine-tuned.

object'fine_tuning.job' required

The object type, which is always "fine_tuning.job".

organization_idstring required

The organization that owns the fine-tuning job.

result_filesstring[] required

The compiled results file ID(s) for the fine-tuning job. You can retrieve the results with the Files API.

The current status of the fine-tuning job, which can be validating_files, queued, running, pausing, paused, succeeded, failed, or cancelled.

trained_tokensinteger nullable required

The total number of billable tokens processed by this fine-tuning job. The value will be null if the fine-tuning job is still running.

training_filestring required

The file ID used for training. You can retrieve the training data with the Files API.

validation_filestring nullable required

The file ID used for validation. You can retrieve the validation results with the Files API.

seedinteger nullable required

The seed used for the fine-tuning job.

estimated_finishinteger nullable

The Unix timestamp (in seconds) for when the fine-tuning job is estimated to finish. The value will be null if the fine-tuning job is not running.