Session Config Options

Agents can provide an arbitrary list of configuration options for a session, allowing Clients to offer users customizable selectors for things like models, modes, reasoning levels, and more.

Session Config Options are the preferred way to expose session-level configuration. If an Agent provides configOptions, Clients SHOULD use them instead of the modes field. Modes will be removed in a future version of the protocol.

Initial State

During Session Setup the Agent MAY return a list of configuration options and their current values:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "sessionId": "sess_abc123def456",
    "configOptions": [
      {
        "id": "mode",
        "name": "Session Mode",
        "description": "Controls how the agent requests permission",
        "category": "mode",
        "type": "select",
        "currentValue": "ask",
        "options": [
          {
            "value": "ask",
            "name": "Ask",
            "description": "Request permission before making any changes"
          },
          {
            "value": "code",
            "name": "Code",
            "description": "Write and modify code with full tool access"
          }
        ]
      },
      {
        "id": "model",
        "name": "Model",
        "category": "model",
        "type": "select",
        "currentValue": "model-1",
        "options": [
          {
            "value": "model-1",
            "name": "Model 1",
            "description": "The fastest model"
          },
          {
            "value": "model-2",
            "name": "Model 2",
            "description": "The most powerful model"
          }
        ]
      }
    ]
  }
}

configOptions

ConfigOption[]

The list of configuration options available for this session. The order of this array represents the Agent’s preferred priority. Clients SHOULD respect this ordering when displaying options.

ConfigOption

string

required

Unique identifier for this configuration option. Used when setting values.

name

string

required

Human-readable label for the option

description

string

Optional description providing more details about what this option controls

ConfigOptionValue

value

string

required

The value identifier used when setting this option

name

string

required

Human-readable name to display

description

string

Optional description of what this value does

Boolean Config Options

Agents MAY include boolean config options only after the Client advertises support during initialization:

{
  "clientCapabilities": {
    "session": {
      "configOptions": {
        "boolean": {}
      }
    }
  }
}

Omitting session, configOptions, or boolean means the Client does not advertise support. When support is advertised, a boolean option uses type: "boolean" and a boolean currentValue:

{
  "id": "brave_mode",
  "name": "Brave Mode",
  "description": "Skip confirmation prompts and act autonomously",
  "type": "boolean",
  "currentValue": true
}

Agents MUST NOT include type: "boolean" options in configOptions payloads unless the Client advertised support. Agents that need to support older Clients should omit the boolean option or provide a select fallback.

Option Categories

Each config option MAY include a category field. Categories are semantic metadata intended to help Clients provide consistent UX, such as attaching keyboard shortcuts, choosing icons, or deciding placement.

Categories are for UX purposes only and MUST NOT be required for correctness. Clients MUST handle missing or unknown categories gracefully.

Category names beginning with _ are free for custom use (e.g., _my_custom_category). Category names that do not begin with _ are reserved for the ACP spec.

Category	Description
`mode`	Session mode selector
`model`	Model selector
`model_config`	Model-related parameter, such as context size or speed/quality trade-off
`thought_level`	Thought/reasoning level selector

Clients SHOULD render model_config options near the model selector, such as in the same popover or panel. No capability negotiation is required for category values. When multiple options share the same category, Clients SHOULD use the array ordering to resolve ties, preferring earlier options in the list for prominent placement or keyboard shortcuts.

Option Ordering

The order of the configOptions array is significant. Agents SHOULD place higher-priority options first in the list. Clients SHOULD:

Display options in the order provided by the Agent
Use ordering to resolve ties when multiple options share the same category
If displaying a limited number of options, prefer those at the beginning of the list

Default Values and Graceful Degradation

Agents MUST always provide a default value for every configuration option. This ensures the Agent can operate correctly even if:

The Client doesn’t support configuration options
The Client chooses not to display certain options
The Client receives an option type it doesn’t recognize

If a Client receives an option with an unrecognized type, it SHOULD ignore that option. The Agent will continue using its default value.

Setting a Config Option

The current value of a config option can be changed at any point during a session, whether the Agent is idle or generating a response.

From the Client

Clients can change a config option value by calling the session/set_config_option method:

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "session/set_config_option",
  "params": {
    "sessionId": "sess_abc123def456",
    "configId": "mode",
    "value": "code"
  }
}

sessionId

SessionId

required

The ID of the session

configId

string

required

The id of the configuration option to change

value

string | boolean

required

The new value to set. For select options, this must be one of the values listed in the option’s options array. For boolean options, this must be a boolean.

For boolean options, Clients send type: "boolean" with a boolean value:

{
  "jsonrpc": "2.0",
  "id": 3,
  "method": "session/set_config_option",
  "params": {
    "sessionId": "sess_abc123def456",
    "configId": "brave_mode",
    "type": "boolean",
    "value": true
  }
}

The Agent MUST respond with the complete list of all configuration options and their current values:

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "configOptions": [
      {
        "id": "mode",
        "name": "Session Mode",
        "type": "select",
        "currentValue": "code",
        "options": [...]
      },
      {
        "id": "model",
        "name": "Model",
        "type": "select",
        "currentValue": "model-1",
        "options": [...]
      }
    ]
  }
}

The response always contains the complete configuration state. This allows Agents to reflect dependent changes. For example, if changing the model affects available reasoning options, or if an option’s available values change based on another selection.

From the Agent

The Agent can also change configuration options and notify the Client by sending a config_option_update session notification:

{
  "jsonrpc": "2.0",
  "method": "session/update",
  "params": {
    "sessionId": "sess_abc123def456",
    "update": {
      "sessionUpdate": "config_option_update",
      "configOptions": [
        {
          "id": "mode",
          "name": "Session Mode",
          "type": "select",
          "currentValue": "code",
          "options": [...]
        },
        {
          "id": "model",
          "name": "Model",
          "type": "select",
          "currentValue": "model-2",
          "options": [...]
        }
      ]
    }
  }
}

This notification also contains the complete configuration state. Common reasons an Agent might update configuration options include:

Switching modes after completing a planning phase
Falling back to a different model due to rate limits or errors
Adjusting available options based on context discovered during execution

Relationship to Session Modes

Session Config Options supersede the older Session Modes API. However, during the transition period, Agents that provide mode-like configuration SHOULD send both:

configOptions with a category: "mode" option for Clients that support config options
modes for Clients that only support the older API

If an Agent provides both configOptions and modes in the session response:

Clients that support config options SHOULD use configOptions exclusively and ignore modes
Clients that don’t support config options SHOULD fall back to modes
Agents SHOULD keep both in sync to ensure consistent behavior regardless of which field the Client uses

Learn about the Session Modes API

Get Started

Protocol

Libraries

Initial State

ConfigOption

ConfigOptionValue

Boolean Config Options

Option Categories

Option Ordering

Default Values and Graceful Degradation

Setting a Config Option

From the Client

From the Agent

Relationship to Session Modes

​Initial State

​ConfigOption

​ConfigOptionValue

​Boolean Config Options

​Option Categories

​Option Ordering

​Default Values and Graceful Degradation

​Setting a Config Option

​From the Client

​From the Agent

​Relationship to Session Modes

Initial State

ConfigOption

ConfigOptionValue

Boolean Config Options

Option Categories

Option Ordering

Default Values and Graceful Degradation

Setting a Config Option

From the Client

From the Agent

Relationship to Session Modes