---
title: "Version history — what this factor has been"
method: GET
path: "/v1/factors/{key}/history"
tags: ["Factors"]
---

# Version history — what this factor has been

`GET /v1/factors/{key}/history`

## Request

- Base URL: `https://api.greencalculus.com`
- URL: `https://api.greencalculus.com/v1/factors/{key}/history`
- Auth: HTTP bearer

Every version the reproducibility archive holds for one key, with the value each version served and whether it was a change or a withdrawal. Derived from the same per-key archive index and the same read that answers ?as_of=, so it cannot disagree with the archive. Requires a key (any tier). History begins at the delta watershed; a short list means a stable factor, and the payload says so.

## Path parameters

- `key` string, required

## Response `200`

Current row + per-version history entries

- FactorHistory
  - `key` string
  - `current` object, nullable: null when the key is withdrawn from the live corpus.
  - `history` object[]
    - `version` string
    - `date` string, nullable
    - `value` number, nullable
    - `unit` string, nullable
    - `kind` 'recorded' | 'withdrawn'
  - `meta` object

## Other responses

- `401`: Missing or invalid API key
- `404`: Key unknown to both the corpus and the archive

---

[API](https://skmtc.dev/greencalculus/apis/greencalculus-api.md) · [All operations](https://skmtc.dev/greencalculus/apis/greencalculus-api/llms.txt) · [OpenAPI document](https://skmtc.dev/greencalculus/apis/greencalculus-api/revisions/2f742325958c?raw)