---
title: "Changes to Messages"
method: POST
path: "/v1/messages"
---

# Changes to Messages

`POST /v1/messages`

> Every recorded change to this operation, newest first.

## Timeline

Changed in 3 of 24 revisions.

- **2026-10-12** `43d7e06a824b`: 1 info
- **2026-09-28** `54da122a2879`: 5 warning, 1 info
- **2026-09-23** `620970c6f5f2`: 11 breaking, 3 warning, 44 info

## Changes

- **2026-10-12** `43d7e06a824b`: 1 info
  - added the non-success response with the status `425`
- **2026-09-28** `54da122a2879`: 5 warning, 1 info
  - removed the request property `effort`
  - removed the request property `models`
  - removed the optional property `pioneer_inference_id` from the response with the `200` status
  - removed the optional property `pioneer_routed_model` from the response with the `200` status
  - removed the optional property `pioneer_savings` from the response with the `200` status
  - added the optional property `fastino_inference_id` to the response with the `200` status
- **2026-09-23** `620970c6f5f2`: 11 breaking, 3 warning, 44 info
  - removed the enum value `assistant` of the request property `messages/items/role`
  - removed the enum value `user` of the request property `messages/items/role`
  - removed `subschema #1, subschema #2` from the `messages/items/content` request property `oneOf` list
  - added `#/components/schemas/HTTPValidationError, #/components/schemas/AnthropicError` to the response body `oneOf` list for the response status `422`
  - the response's body type changed from `object` to no type for status `422`
  - removed the media type `text/event-stream` for the response with the status `200`
  - the response property `role` became optional for the status `200`
  - the response property `stop_reason` became optional for the status `200`
  - the response property `type` became optional for the status `200`
  - response property `stop_reason` list-of-types was widened by adding types `null` to media type `application/json` of response `200`
  - response property `stop_sequence` list-of-types was widened by adding types `null` to media type `application/json` of response `200`
  - removed the optional property `content/items/text` from the response with the `200` status
  - removed the optional property `content/items/type` from the response with the `200` status
  - removed the optional property `detail` from the response with the `422` status
  - api operation id `create_message` removed and replaced with `messages_v1_messages_post`
  - added the new optional request property `cache_control`
  - added the new optional request property `effort`
  - added the new optional request property `include_confidence`
  - added the new optional request property `include_spans`
  - added the new optional request property `models`
  - added the new optional request property `output_config`
  - added the new optional request property `speed`
  - added the new optional request property `task_type`
  - added `subschema #1, subschema #2` to the `messages/items/content` request property `anyOf` list
  - the request property `max_tokens` became optional
  - request property `schema` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `stop_sequences` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `system` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `temperature` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `thinking` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `tool_choice` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `tools` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `top_k` list-of-types was widened by adding types `null` to media type `application/json`
  - request property `top_p` list-of-types was widened by adding types `null` to media type `application/json`
  - removed the non-success response with the status `401`
  - removed the non-success response with the status `402`
  - removed the non-success response with the status `404`
  - removed the non-success response with the status `429`
  - added the optional property `pioneer_inference_id` to the response with the `200` status
  - added the optional property `pioneer_routed_model` to the response with the `200` status
  - …18 more

---

[Operation](https://skmtc.dev/fastino-ai/apis/pioneer-inference-api/docs/v1/messages/post.md) - [API](https://skmtc.dev/fastino-ai/apis/pioneer-inference-api.md) - [Page](https://skmtc.dev/fastino-ai/apis/pioneer-inference-api/changes/v1/messages/post)