---
schema_version: "1"
id: 8c535192d21dd146919dbb88d7e930908d92862edca124bb6e55df0e03f00039
title: Legacy Agent Builder Changing Reasoning Engine from GPT-4o to GPT-5.6 Luna
collection: admin
version: current
locale: en-us
portal_url: https://docs.salesforce.com/admin/current/en-us/release-notes/264-0-0/rn_einstein_models_legacy_builder_model_change.md
canonical_url: https://help.salesforce.com/s/articleView?id=release-notes.rn_einstein_models_legacy_builder_model_change.htm&release=264.0.0&type=5
source_site: help.salesforce.com
content_type: documentation
content_hash: eb843c1febe7c79e593605f8a8515b2fdc50a7435c6a3af38919a82def9fa915
description: The legacy Agentforce Builder is implementing an on/off switch to change the reasoning engine to GPT-5.6 Luna on October 15, 2026.
products:
  - Cross Cloud
release: "264"
---
# Legacy Agent Builder Changing Reasoning Engine from GPT-4o to GPT-5.6 Luna

The legacy Agentforce Builder is implementing an on/off switch to change the reasoning engine to GPT-5.6 Luna on October 15, 2026.

Changing the reasoning engine requires weeks of testing to ensure continued functionality and expected behavior. To avoid extra testing in the future, we recommend upgrading to the new Agentforce Builder to unlock enhanced features, ensure long-term support, and avoid extra testing for the model switch. To learn more, [Upgrade an Agent from the Legacy Builder to the New Builder](https://help.salesforce.com/s/articleView?id=ai.agent_setup_create_upgrade.htm&language=en_US).

If you don't want to upgrade to the new builder, you must change the legacy builder reasoning engine to GPT-5.6 Luna and test extensively:

1. From the App Launcher, enter `agentforce agents`, and then select **Agentforce Agents**.
2. Click the name of the agent you want to change, then click the edit icon next to **Description**.
3. At the end of the agent description, add the following text: `#agent_new_gpt_model:on#`. If this text is not in the description, the agent will continue to use GPT-4o.
4. Click **Save**.
5. Test your agent in Preview, then on a sandbox org, then move the change to production when you're ready.

![Add #agent\_new\_gpt\_model:on# to the agent description to change the reasoning model to GPT-5.6 Luna.](https://sf-zdocs-cdn-prod.zoominsoftware.com/tdta-release-notes-salesforce_release_notes-264-0-0-production-enus/550ba85b-db1a-4608-9cd4-9a65ec96e1fa/salesforce_release_notes/images/agentforce/rn_264_agentforce_legacy_upgrade_1.png)

**Where:** This change applies to Lightning Experience in Enterprise, Performance, and Unlimited editions with Foundations or Agentforce 1 editions.

**When:** Change is available on a rolling basis in Salesforce orgs upgraded to Winter ’27 starting the week of October 12, 2026.

**Why:** This change is in preparation for OpenAI GPT-4o’s deprecation in Spring 2027. After that, all legacy builder reasoning engines will be automatically changed to GPT-5.6 Luna. Test now to avoid distruptions.

#### See Also

- [_Salesforce Help_: Upgrade an Agent from the Legacy Builder to the New Builder](https://help.salesforce.com/s/articleView?id=ai.agent_setup_create_upgrade.htm&language=en_US)