Choosing a style for the agent

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The agent style you select determines how your agent processes requests, calls tools, and manages context across steps. Use ReAct Core for all new and existing agents. Default and ReAct are deprecated as of July 15, 2026.

Available agent styles

Table 1. Agent styles
Style Description
ReAct Core (Recommended)

Follows a think, act, and observe pattern using the model's native tool calling and reasoning capabilities, with focused context management for each task.
Default (Deprecated) Uses the model's built-in capabilities to understand, plan, and use tools and knowledge.
ReAct (Deprecated) Enables the model to think, act, observe, and refine its approach until a task is completed.
Important:

Default and ReAct are deprecated. Migrate your agents to ReAct Core. For migration steps, see Migrating to ReAct Core agent style.

ReAct Core

ReAct Core follows a think, act, and observe pattern using the model's native tool calling and reasoning capabilities. Unlike Default and ReAct, it does not pass the full conversation history, each step receives only the context relevant to that task. This focused context management improves accuracy, especially for complex and multi-step tasks. For more information, see Context sharing with collaborator agents.

The think, act, and observe pattern works as follows:

  • Think: Assesses the request, determines the relevant context, and decides the next action.
  • Act: Calls a tool or takes an action using the context for that step.
  • Observe: Evaluates the result and determines whether to act again or return a response.

ReAct Core works with Python tools, OpenAPI tools, MCP tools, knowledge bases, and collaborator agents. It is recommended for use with gpt-oss-120b. If you use a Llama or other open-source model, test your agent thoroughly after migrating. For details, see Scenario 2: Migrate agents that use Default or ReAct with other models.

Tip:

If you select gpt-oss-120b as your model, ReAct Core applies automatically regardless of which style you select in the UI.

Deprecated styles

The following styles are deprecated and will be removed in a future release. Migrate to ReAct Core. For migration steps, see Migrating to ReAct Core agent style.

Default

Uses the model's built-in capabilities to understand, plan, and use tools and knowledge. If you use gpt-oss-120b, your agent already runs on ReAct Core internally even when Default is selected.

ReAct

Enables the model to think, act, observe, and refine its approach until a task is completed.

Setting the style in the UI

  1. In the Profile section, go to Agent style.

  2. Select ReAct Core.

Tip:

If the style shows an Agent style set from ADK notification, the style was set in the ADK and you cannot change it in the UI. To configure the style, update the agent in the ADK. For more information, see Agent styles.

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