> ## Documentation Index
> Fetch the complete documentation index at: https://developers.openalex.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Deprecations

> Deprecated features and migration guides

This page is a centralized reference for all deprecated features in the OpenAlex API. Use it to migrate old code and avoid using features that will be removed.

## Already Removed

These features have been removed from the API. Using them will cause errors.

### `host_venue` and `alternate_host_venues`

**Removed:** These Work object properties no longer exist.

**Replacement:** Use `primary_location` and `locations` instead.

**Migration:**

```diff theme={"dark"}
- work.host_venue.display_name
+ work.primary_location.source.display_name

- work.alternate_host_venues
+ work.locations
```

**Filter changes:**

```diff theme={"dark"}
- filter=host_venue.id:S123
+ filter=primary_location.source.id:S123

- filter=host_venue.publisher:P123
+ filter=primary_location.source.host_organization:P123
```

### `grants`

**Removed:** The `grants` property on Works has been removed.

**Replacement:** Use `funders` and `awards` for more comprehensive funding data.

**Migration:**

```diff theme={"dark"}
- work.grants[0].funder
+ work.funders[0].display_name

- work.grants[0].award_id
+ work.awards[0].funder_award_id
```

The new `awards` entity provides detailed award information including DOIs when available.

### `has_ngrams` filter

**Removed:** This filter no longer works.

**Replacement:** Use `has_fulltext` instead.

```diff theme={"dark"}
- filter=has_ngrams:true
+ filter=has_fulltext:true
```

## Deprecated (Still Working)

These features still work but are not recommended. They will be removed in the future.

### Concepts Entity

<Warning>
  Concepts are deprecated in favor of **Topics**. We will continue to provide Concepts on Works, but we are not actively maintaining, updating, or providing support for them.
</Warning>

**Replacement:** Use [Topics](/api-reference/topics) instead.

**Why Topics are better:**

| Feature   | Concepts                 | Topics                                       |
| --------- | ------------------------ | -------------------------------------------- |
| Count     | \~65,000                 | \~4,500                                      |
| Hierarchy | 6 levels                 | 4 levels (domain → field → subfield → topic) |
| Source    | Microsoft Academic Graph | OpenAlex native (with CWTS)                  |
| Status    | Deprecated               | Active                                       |

**Migration:**

| Concepts                  | Topics                  |
| ------------------------- | ----------------------- |
| `work.concepts`           | `work.topics`           |
| `work.concepts[0].id`     | `work.primary_topic.id` |
| `/concepts` endpoint      | `/topics` endpoint      |
| `filter=concepts.id:C123` | `filter=topics.id:T123` |

```diff theme={"dark"}
- /works?filter=concepts.id:C86803240
+ /works?filter=topics.id:T10234
```

### `x_concepts` on Entities

**Deprecated:** The `x_concepts` property on Authors, Sources, and Institutions will be removed.

**Replacement:** Use Topics-based filtering and aggregation instead.

```diff theme={"dark"}
- author.x_concepts
+ # Use: /works?filter=authorships.author.id:A123&group_by=topics.id
```

### `last_known_institution` (singular)

**Deprecated:** The singular `last_known_institution` on Authors is deprecated.

**Replacement:** Use `last_known_institutions` (plural) instead.

```diff theme={"dark"}
- author.last_known_institution
+ author.last_known_institutions[0]
```

The plural form supports authors with multiple current affiliations.

### `/text` Endpoint (Aboutness)

<Warning>
  The `/text` endpoint is deprecated and not recommended for new projects.
</Warning>

**What it did:** Classified arbitrary text into Topics and Keywords.

**Cost:** \$0.01 per request.

**Status:** Still functional but will not receive updates or support.

If you need topic classification, consider:

* Using the Topics already assigned to works in OpenAlex
* Building your own classifier using OpenAlex Topics as training data

## Filter Aliases (Deprecated)

These filter aliases still work but use the canonical form instead:

| Deprecated      | Use Instead |
| --------------- | ----------- |
| `concept.id`    | `topics.id` |
| `concepts.id`   | `topics.id` |
| `x_concepts.id` | `topics.id` |

## Historical: Polite Pool

Before February 2026, OpenAlex used a "polite pool" system where you could get higher rate limits by including `mailto=you@example.com` in your requests.

**This system has been replaced by API keys.**

* The `mailto` parameter is ignored
* All users need an [API key](/guides/authentication) (free)
* See the [announcement](https://groups.google.com/g/openalex-users/c/rI1GIAySpVQ) for details

## Timeline

| Feature          | Status     | Action Required                 |
| ---------------- | ---------- | ------------------------------- |
| `host_venue`     | Removed    | Migrate to `primary_location`   |
| `grants`         | Removed    | Migrate to `funders` / `awards` |
| `has_ngrams`     | Removed    | Migrate to `has_fulltext`       |
| Concepts         | Deprecated | Migrate to Topics               |
| `x_concepts`     | Deprecated | Will be removed soon            |
| `/text` endpoint | Deprecated | Not recommended                 |
| Polite pool      | Replaced   | Use API keys                    |

## Staying Updated

For announcements about deprecations and breaking changes:

* Join the [OpenAlex User Group](https://groups.google.com/g/openalex-users)
* Follow [@OpenAlex\_org](https://twitter.com/openalex_org) on Twitter
* Check the [OpenAlex User Group](https://groups.google.com/g/openalex-users) for announcements