---
title: "Create a chunk-completion row on a TrainingSession (per-chunk distributions, dataset refs, checkpoints). Trainer-driven write; the server validates the parent session and materializes the row."
method: POST
path: "/v1/accounts/{account_id}/trainingSessions/{training_session_id}/chunkOutputs"
tags: ["gateway.openapi_Gateway"]
---

# Create a chunk-completion row on a TrainingSession (per-chunk distributions, dataset refs, checkpoints). Trainer-driven write; the server validates the parent session and materializes the row.

`POST /v1/accounts/{account_id}/trainingSessions/{training_session_id}/chunkOutputs`

## Request

- Base URL: `https://api.fireworks.ai`
- URL: `https://api.fireworks.ai/v1/accounts/{account_id}/trainingSessions/{training_session_id}/chunkOutputs`
- Auth: HTTP bearer
- TypeScript: <https://skmtc.dev/fw-ai-external/apis/gateway-rest-api/docs/v1/accounts/:account_id/trainingSessions/:training_session_id/chunkOutputs/post.ts> (a function with typed inputs; its response is checked against the schema)

## Path parameters

- `account_id` string, required
- `training_session_id` string, required

## Query parameters

- `trainingSessionChunkOutputId` string

## Request body

- GatewayTrainingSessionChunkOutput
  - `name` string
  - `step` integer
  - `endOfEpoch` boolean
  - `outputDatasetName` string
  - `checkpointPath` string: Server-signed URL (24h TTL) suitable for direct browser download. Empty string when signing is unavailable for the underlying object.
  - `epochStreamlogPath` string: Server-signed URL (24h TTL). Empty when signing is unavailable.
  - `distribution` GatewayDistributionSnapshot
    - `metrics` object: Keyed by metric name (e.g. "reward", "format_valid").
    - `correlation` GatewayCorrelationMatrix: CorrelationMatrix is a square matrix; rows[i].values[j] is the Pearson correlation between labels[i] and labels[j].
      - `labels` string[]
      - `rows` GatewayCorrelationRow[]
        - `values` number[]
  - `epochId` string
  - `createTime` string, date-time
  - `updateTime` string, date-time

## Response `200`

A successful response.

- GatewayTrainingSessionChunkOutput
  - `name` string
  - `step` integer
  - `endOfEpoch` boolean
  - `outputDatasetName` string
  - `checkpointPath` string: Server-signed URL (24h TTL) suitable for direct browser download. Empty string when signing is unavailable for the underlying object.
  - `epochStreamlogPath` string: Server-signed URL (24h TTL). Empty when signing is unavailable.
  - `distribution` GatewayDistributionSnapshot
    - `metrics` object: Keyed by metric name (e.g. "reward", "format_valid").
    - `correlation` GatewayCorrelationMatrix: CorrelationMatrix is a square matrix; rows[i].values[j] is the Pearson correlation between labels[i] and labels[j].
      - `labels` string[]
      - `rows` GatewayCorrelationRow[]
        - `values` number[]
  - `epochId` string
  - `createTime` string, date-time
  - `updateTime` string, date-time

## Changes

- **2026-10-16** `3bf245180173`: 1 info
  - endpoint added

[Operation history](https://skmtc.dev/fw-ai-external/apis/gateway-rest-api/changes/v1/accounts/:account_id/trainingSessions/:training_session_id/chunkOutputs/post.md)

---

[API](https://skmtc.dev/fw-ai-external/apis/gateway-rest-api.md) - [All operations](https://skmtc.dev/fw-ai-external/apis/gateway-rest-api/llms.txt) - [OpenAPI document](https://skmtc.dev/fw-ai-external/apis/gateway-rest-api/revisions/3bf245180173?raw)