feat: add reasoning_effort support to all SDK clients

- Add reasoningEffort to SessionConfig and ResumeSessionConfig
- Extend ModelCapabilities.supports with reasoningEffort flag
- Add supportedReasoningEfforts and defaultReasoningEffort to ModelInfo
- Update session create/resume to pass reasoningEffort to server

Author: friggeri

dotnet/src/Client.cs

@@ -347,6 +347,7 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig? config = nul
         var request = new CreateSessionRequest(
             config?.Model,
             config?.SessionId,
+            config?.ReasoningEffort,
             config?.Tools?.Select(ToolDefinition.FromAIFunction).ToList(),
             config?.SystemMessage,
             config?.AvailableTools,
@@ -428,6 +429,7 @@ public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSes
 
         var request = new ResumeSessionRequest(
             sessionId,
+            config?.ReasoningEffort,
             config?.Tools?.Select(ToolDefinition.FromAIFunction).ToList(),
             config?.Provider,
             config?.OnPermissionRequest != null ? true : null,
@@ -1090,6 +1092,7 @@ public static string Escape(string arg)
     internal record CreateSessionRequest(
         string? Model,
         string? SessionId,
+        string? ReasoningEffort,
         List<ToolDefinition>? Tools,
         SystemMessageConfig? SystemMessage,
         List<string>? AvailableTools,
@@ -1122,6 +1125,7 @@ internal record CreateSessionResponse(
 
     internal record ResumeSessionRequest(
         string SessionId,
+        string? ReasoningEffort,
         List<ToolDefinition>? Tools,
         ProviderConfig? Provider,
         bool? RequestPermission,

dotnet/src/Types.cs

@@ -692,6 +692,13 @@ public class SessionConfig
     public string? SessionId { get; set; }
     public string? Model { get; set; }
 
+    /// <summary>
+    /// Reasoning effort level for models that support it.
+    /// Valid values: "low", "medium", "high", "xhigh".
+    /// Only applies to models where capabilities.supports.reasoningEffort is true.
+    /// </summary>
+    public string? ReasoningEffort { get; set; }
+
     /// <summary>
     /// Override the default configuration directory location.
     /// When specified, the session will use this directory for storing config and state.
@@ -766,6 +773,12 @@ public class ResumeSessionConfig
     public ICollection<AIFunction>? Tools { get; set; }
     public ProviderConfig? Provider { get; set; }
 
+    /// <summary>
+    /// Reasoning effort level for models that support it.
+    /// Valid values: "low", "medium", "high", "xhigh".
+    /// </summary>
+    public string? ReasoningEffort { get; set; }
+
     /// <summary>
     /// Handler for permission requests from the server.
     /// When provided, the server will call this handler to request permission for operations.
@@ -930,6 +943,12 @@ public class ModelSupports
 {
     [JsonPropertyName("vision")]
     public bool Vision { get; set; }
+
+    /// <summary>
+    /// Whether this model supports reasoning effort configuration.
+    /// </summary>
+    [JsonPropertyName("reasoningEffort")]
+    public bool ReasoningEffort { get; set; }
 }
 
 /// <summary>
@@ -989,6 +1008,14 @@ public class ModelInfo
     /// <summary>Billing information</summary>
     [JsonPropertyName("billing")]
     public ModelBilling? Billing { get; set; }
+
+    /// <summary>Supported reasoning effort levels (only present if model supports reasoning effort)</summary>
+    [JsonPropertyName("supportedReasoningEfforts")]
+    public List<string>? SupportedReasoningEfforts { get; set; }
+
+    /// <summary>Default reasoning effort level (only present if model supports reasoning effort)</summary>
+    [JsonPropertyName("defaultReasoningEffort")]
+    public string? DefaultReasoningEffort { get; set; }
 }
 
 /// <summary>

go/client.go

@@ -461,6 +461,9 @@ func (c *Client) CreateSession(config *SessionConfig) (*Session, error) {
 		if config.SessionID != "" {
 			params["sessionId"] = config.SessionID
 		}
+		if config.ReasoningEffort != "" {
+			params["reasoningEffort"] = config.ReasoningEffort
+		}
 		if len(config.Tools) > 0 {
 			toolDefs := make([]map[string]interface{}, 0, len(config.Tools))
 			for _, tool := range config.Tools {
@@ -670,6 +673,9 @@ func (c *Client) ResumeSessionWithOptions(sessionID string, config *ResumeSessio
 	}
 
 	if config != nil {
+		if config.ReasoningEffort != "" {
+			params["reasoningEffort"] = config.ReasoningEffort
+		}
 		if len(config.Tools) > 0 {
 			toolDefs := make([]map[string]interface{}, 0, len(config.Tools))
 			for _, tool := range config.Tools {

go/types.go

@@ -322,6 +322,10 @@ type SessionConfig struct {
 	SessionID string
 	// Model to use for this session
 	Model string
+	// ReasoningEffort level for models that support it.
+	// Valid values: "low", "medium", "high", "xhigh"
+	// Only applies to models where capabilities.supports.reasoningEffort is true.
+	ReasoningEffort string
 	// ConfigDir overrides the default configuration directory location.
 	// When specified, the session will use this directory for storing config and state.
 	ConfigDir string
@@ -399,6 +403,9 @@ type ResumeSessionConfig struct {
 	Tools []Tool
 	// Provider configures a custom model provider
 	Provider *ProviderConfig
+	// ReasoningEffort level for models that support it.
+	// Valid values: "low", "medium", "high", "xhigh"
+	ReasoningEffort string
 	// OnPermissionRequest is a handler for permission requests from the server
 	OnPermissionRequest PermissionHandler
 	// OnUserInputRequest is a handler for user input requests from the agent (enables ask_user tool)
@@ -523,7 +530,8 @@ type ModelLimits struct {
 
 // ModelSupports contains model support flags
 type ModelSupports struct {
-	Vision bool `json:"vision"`
+	Vision          bool `json:"vision"`
+	ReasoningEffort bool `json:"reasoningEffort"`
 }
 
 // ModelCapabilities contains model capabilities and limits
@@ -545,11 +553,13 @@ type ModelBilling struct {
 
 // ModelInfo contains information about an available model
 type ModelInfo struct {
-	ID           string            `json:"id"`
-	Name         string            `json:"name"`
-	Capabilities ModelCapabilities `json:"capabilities"`
-	Policy       *ModelPolicy      `json:"policy,omitempty"`
-	Billing      *ModelBilling     `json:"billing,omitempty"`
+	ID                        string            `json:"id"`
+	Name                      string            `json:"name"`
+	Capabilities              ModelCapabilities `json:"capabilities"`
+	Policy                    *ModelPolicy      `json:"policy,omitempty"`
+	Billing                   *ModelBilling     `json:"billing,omitempty"`
+	SupportedReasoningEfforts []string          `json:"supportedReasoningEfforts,omitempty"`
+	DefaultReasoningEffort    string            `json:"defaultReasoningEffort,omitempty"`
 }
 
 // GetModelsResponse is the response from models.list

nodejs/package-lock.json

@@ -40,7 +40,7 @@
   "author": "GitHub",
   "license": "MIT",
   "dependencies": {
-    "@github/copilot": "^0.0.399",
+    "@github/copilot": "^0.0.400",
     "vscode-jsonrpc": "^8.2.1",
     "zod": "^4.3.5"
   },

nodejs/package.json

@@ -452,6 +452,7 @@ export class CopilotClient {
         const response = await this.connection!.sendRequest("session.create", {
             model: config.model,
             sessionId: config.sessionId,
+            reasoningEffort: config.reasoningEffort,
             tools: config.tools?.map((tool) => ({
                 name: tool.name,
                 description: tool.description,
@@ -531,6 +532,7 @@ export class CopilotClient {
 
         const response = await this.connection!.sendRequest("session.resume", {
             sessionId,
+            reasoningEffort: config.reasoningEffort,
             tools: config.tools?.map((tool) => ({
                 name: tool.name,
                 description: tool.description,

nodejs/src/client.ts

@@ -603,6 +603,11 @@ export interface InfiniteSessionConfig {
     bufferExhaustionThreshold?: number;
 }
 
+/**
+ * Valid reasoning effort levels for models that support it.
+ */
+export type ReasoningEffort = "low" | "medium" | "high" | "xhigh";
+
 export interface SessionConfig {
     /**
      * Optional custom session ID
@@ -615,6 +620,13 @@ export interface SessionConfig {
      */
     model?: string;
 
+    /**
+     * Reasoning effort level for models that support it.
+     * Only valid for models where capabilities.supports.reasoningEffort is true.
+     * Use client.listModels() to check supported values for each model.
+     */
+    reasoningEffort?: ReasoningEffort;
+
     /**
      * Override the default configuration directory location.
      * When specified, the session will use this directory for storing config and state.
@@ -721,6 +733,7 @@ export type ResumeSessionConfig = Pick<
     | "tools"
     | "provider"
     | "streaming"
+    | "reasoningEffort"
     | "onPermissionRequest"
     | "onUserInputRequest"
     | "hooks"
@@ -876,6 +889,8 @@ export interface GetAuthStatusResponse {
 export interface ModelCapabilities {
     supports: {
         vision: boolean;
+        /** Whether this model supports reasoning effort configuration */
+        reasoningEffort: boolean;
     };
     limits: {
         max_prompt_tokens?: number;
@@ -917,4 +932,8 @@ export interface ModelInfo {
     policy?: ModelPolicy;
     /** Billing information */
     billing?: ModelBilling;
+    /** Supported reasoning effort levels (only present if model supports reasoning effort) */
+    supportedReasoningEfforts?: ReasoningEffort[];
+    /** Default reasoning effort level (only present if model supports reasoning effort) */
+    defaultReasoningEffort?: ReasoningEffort;
 }

nodejs/src/types.ts

@@ -387,6 +387,8 @@ async def create_session(self, config: Optional[SessionConfig] = None) -> Copilo
             payload["model"] = cfg["model"]
         if cfg.get("session_id"):
             payload["sessionId"] = cfg["session_id"]
+        if cfg.get("reasoning_effort"):
+            payload["reasoningEffort"] = cfg["reasoning_effort"]
         if tool_defs:
             payload["tools"] = tool_defs
 
@@ -545,6 +547,8 @@ async def resume_session(
                 tool_defs.append(definition)
 
         payload: dict[str, Any] = {"sessionId": session_id}
+        if cfg.get("reasoning_effort"):
+            payload["reasoningEffort"] = cfg["reasoning_effort"]
         if tool_defs:
             payload["tools"] = tool_defs