feat: add reasoning_effort support to all SDK clients

dotnet/README.md

@@ -93,6 +93,7 @@ Create a new conversation session.
 
 - `SessionId` - Custom session ID
 - `Model` - Model to use ("gpt-5", "claude-sonnet-4.5", etc.)
+- `ReasoningEffort` - Reasoning effort level for models that support it ("low", "medium", "high", "xhigh"). Use `ListModelsAsync()` to check which models support this option.
 - `Tools` - Custom tools exposed to the CLI
 - `SystemMessage` - System message customization
 - `AvailableTools` - List of tool names to allow

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/README.md

@@ -102,6 +102,7 @@ func main() {
 **SessionConfig:**
 
 - `Model` (string): Model to use ("gpt-5", "claude-sonnet-4.5", etc.). **Required when using custom provider.**
+- `ReasoningEffort` (string): Reasoning effort level for models that support it ("low", "medium", "high", "xhigh"). Use `ListModels()` to check which models support this option.
 - `SessionID` (string): Custom session ID
 - `Tools` ([]Tool): Custom tools exposed to the CLI
 - `SystemMessage` (\*SystemMessageConfig): System message configuration
@@ -114,6 +115,7 @@ func main() {
 **ResumeSessionConfig:**
 
 - `Tools` ([]Tool): Tools to expose when resuming
+- `ReasoningEffort` (string): Reasoning effort level for models that support it
 - `Provider` (\*ProviderConfig): Custom API provider configuration (BYOK). See [Custom Providers](#custom-providers) section.
 - `Streaming` (bool): Enable streaming delta events
 

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/README.md

@@ -86,8 +86,9 @@ Create a new conversation session.
 
 **Config:**
 
-- `sessionId?: string` - Custom session ID
+- `sessionId?: string` - Custom session ID.
 - `model?: string` - Model to use ("gpt-5", "claude-sonnet-4.5", etc.). **Required when using custom provider.**
+- `reasoningEffort?: "low" | "medium" | "high" | "xhigh"` - Reasoning effort level for models that support it. Use `listModels()` to check which models support this option.
 - `tools?: Tool[]` - Custom tools exposed to the CLI
 - `systemMessage?: SystemMessageConfig` - System message customization (see below)
 - `infiniteSessions?: InfiniteSessionConfig` - Configure automatic context compaction (see below)
@@ -511,12 +512,12 @@ const session = await client.createSession({
         // request.question - The question to ask
         // request.choices - Optional array of choices for multiple choice
         // request.allowFreeform - Whether freeform input is allowed (default: true)
-        
+
         console.log(`Agent asks: ${request.question}`);
         if (request.choices) {
             console.log(`Choices: ${request.choices.join(", ")}`);
         }
-        
+
         // Return the user's response
         return {
             answer: "User's answer here",
@@ -544,7 +545,7 @@ const session = await client.createSession({
                 additionalContext: "Extra context for the model",
             };
         },
-        
+
         // Called after each tool execution
         onPostToolUse: async (input, invocation) => {
             console.log(`Tool ${input.toolName} completed`);
@@ -553,28 +554,28 @@ const session = await client.createSession({
                 additionalContext: "Post-execution notes",
             };
         },
-        
+
         // Called when user submits a prompt
         onUserPromptSubmitted: async (input, invocation) => {
             console.log(`User prompt: ${input.prompt}`);
             return {
                 modifiedPrompt: input.prompt, // Optionally modify the prompt
             };
         },
-        
+
         // Called when session starts
         onSessionStart: async (input, invocation) => {
             console.log(`Session started from: ${input.source}`); // "startup", "resume", "new"
             return {
                 additionalContext: "Session initialization context",
             };
         },
-        
+
         // Called when session ends
         onSessionEnd: async (input, invocation) => {
             console.log(`Session ended: ${input.reason}`);
         },
-        
+
         // Called when an error occurs
         onErrorOccurred: async (input, invocation) => {
             console.error(`Error in ${input.errorContext}: ${input.error}`);

nodejs/package.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/src/client.ts

@@ -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,