Add token limit fields to ProviderConfig across all SDKs

Add maxOutputTokens, maxPromptTokens, maxContextWindowTokens, and
modelLimitsId to ProviderConfig in Node.js, Python, .NET, and Go SDKs.
These optional fields allow BYOK users to configure token limits for
custom providers, matching the runtime's ProviderConfig (PR #5311).

Also update the Python wire format conversion to map the new snake_case
fields to camelCase for the JSON-RPC wire protocol.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MackinnonBuck

dotnet/src/Types.cs

@@ -1115,6 +1115,35 @@ public class ProviderConfig
     /// </summary>
     [JsonPropertyName("azure")]
     public AzureOptions? Azure { get; set; }
+
+    /// <summary>
+    /// Overrides the maximum number of output tokens the model can generate.
+    /// When set, takes precedence over the default limit resolved from the model's capability catalog entry.
+    /// </summary>
+    [JsonPropertyName("maxOutputTokens")]
+    public int? MaxOutputTokens { get; set; }
+
+    /// <summary>
+    /// Overrides the maximum number of prompt/input tokens.
+    /// When set, takes precedence over the default limit resolved from the model's capability catalog entry.
+    /// </summary>
+    [JsonPropertyName("maxPromptTokens")]
+    public int? MaxPromptTokens { get; set; }
+
+    /// <summary>
+    /// Overrides the maximum context window size in tokens.
+    /// When set, takes precedence over the default limit resolved from the model's capability catalog entry.
+    /// </summary>
+    [JsonPropertyName("maxContextWindowTokens")]
+    public int? MaxContextWindowTokens { get; set; }
+
+    /// <summary>
+    /// Specifies the model ID used to look up default token limits from the capability catalog.
+    /// When unset, the session's configured model ID (see <see cref="SessionConfig.Model"/>) is used.
+    /// This is useful for fine-tuned models that share the same limits as a base model.
+    /// </summary>
+    [JsonPropertyName("modelLimitsId")]
+    public string? ModelLimitsId { get; set; }
 }
 
 /// <summary>

go/types.go

@@ -601,6 +601,19 @@ type ProviderConfig struct {
 	BearerToken string `json:"bearerToken,omitempty"`
 	// Azure contains Azure-specific options
 	Azure *AzureProviderOptions `json:"azure,omitempty"`
+	// MaxOutputTokens overrides the maximum number of output tokens the model can generate.
+	// When set, takes precedence over the default limit from the model's capability catalog entry.
+	MaxOutputTokens int `json:"maxOutputTokens,omitempty"`
+	// MaxPromptTokens overrides the maximum number of prompt/input tokens.
+	// When set, takes precedence over the default limit from the model's capability catalog entry.
+	MaxPromptTokens int `json:"maxPromptTokens,omitempty"`
+	// MaxContextWindowTokens overrides the maximum context window size in tokens.
+	// When set, takes precedence over the default limit from the model's capability catalog entry.
+	MaxContextWindowTokens int `json:"maxContextWindowTokens,omitempty"`
+	// ModelLimitsId specifies the model ID used to look up default token limits from the capability catalog.
+	// When unset, the session's configured model ID is used.
+	// Useful for fine-tuned models that share the same limits as a base model.
+	ModelLimitsId string `json:"modelLimitsId,omitempty"`
 }
 
 // AzureProviderOptions contains Azure-specific provider configuration

nodejs/src/types.ts

@@ -1260,6 +1260,31 @@ export interface ProviderConfig {
          */
         apiVersion?: string;
     };
+
+    /**
+     * Overrides the maximum number of output tokens the model can generate.
+     * When set, takes precedence over the default limit resolved from the model's capability catalog entry.
+     */
+    maxOutputTokens?: number;
+
+    /**
+     * Overrides the maximum number of prompt/input tokens.
+     * When set, takes precedence over the default limit resolved from the model's capability catalog entry.
+     */
+    maxPromptTokens?: number;
+
+    /**
+     * Overrides the maximum context window size in tokens.
+     * When set, takes precedence over the default limit resolved from the model's capability catalog entry.
+     */
+    maxContextWindowTokens?: number;
+
+    /**
+     * Specifies the model ID used to look up default token limits from the capability catalog.
+     * When unset, the session's configured model ID is used.
+     * This is useful for fine-tuned models that share the same limits as a base model.
+     */
+    modelLimitsId?: string;
 }
 
 /**

python/copilot/client.py

@@ -1962,6 +1962,16 @@ def _convert_provider_to_wire_format(
                 wire_azure["apiVersion"] = azure["api_version"]
             if wire_azure:
                 wire_provider["azure"] = wire_azure
+        if "max_output_tokens" in provider:
+            wire_provider["maxOutputTokens"] = provider["max_output_tokens"]
+        if "max_prompt_tokens" in provider:
+            wire_provider["maxPromptTokens"] = provider["max_prompt_tokens"]
+        if "max_context_window_tokens" in provider:
+            wire_provider["maxContextWindowTokens"] = provider[
+                "max_context_window_tokens"
+            ]
+        if "model_limits_id" in provider:
+            wire_provider["modelLimitsId"] = provider["model_limits_id"]
         return wire_provider
 
     def _convert_custom_agent_to_wire_format(

python/copilot/session.py

@@ -507,6 +507,19 @@ class ProviderConfig(TypedDict, total=False):
     # Takes precedence over api_key when both are set.
     bearer_token: str
     azure: AzureProviderOptions  # Azure-specific options
+    # Overrides the maximum number of output tokens the model can generate.
+    # Takes precedence over the default limit from the model's capability catalog entry.
+    max_output_tokens: int
+    # Overrides the maximum number of prompt/input tokens.
+    # Takes precedence over the default limit from the model's capability catalog entry.
+    max_prompt_tokens: int
+    # Overrides the maximum context window size in tokens.
+    # Takes precedence over the default limit from the model's capability catalog entry.
+    max_context_window_tokens: int
+    # Model ID used to look up default token limits from the capability catalog.
+    # When unset, the session's configured model ID is used.
+    # Useful for fine-tuned models that share the same limits as a base model.
+    model_limits_id: str
 
 
 class SessionConfig(TypedDict, total=False):