diff --git a/src/agents/model-compat.test.ts b/src/agents/model-compat.test.ts
index c742ae643b7..0ef5bacbe73 100644
--- a/src/agents/model-compat.test.ts
+++ b/src/agents/model-compat.test.ts
@@ -157,6 +157,19 @@ describe("normalizeModelCompat", () => {
     });
   });
 
+  it("keeps supportsUsageInStreaming on for native ModelStudio endpoints", () => {
+    const model = {
+      ...baseModel(),
+      provider: "modelstudio",
+      baseUrl: "https://dashscope-intl.aliyuncs.com/compatible-mode/v1",
+    };
+    delete (model as { compat?: unknown }).compat;
+    const normalized = normalizeModelCompat(model);
+    expect(supportsDeveloperRole(normalized)).toBe(false);
+    expect(supportsUsageInStreaming(normalized)).toBe(true);
+    expect(supportsStrictMode(normalized)).toBe(false);
+  });
+
   it("leaves native api.openai.com model untouched", () => {
     const model = {
       ...baseModel(),
diff --git a/src/agents/openai-completions-compat.ts b/src/agents/openai-completions-compat.ts
index 99879c08210..1f3b136ce2d 100644
--- a/src/agents/openai-completions-compat.ts
+++ b/src/agents/openai-completions-compat.ts
@@ -13,6 +13,8 @@ export type OpenAICompletionsCompatDefaults = {
   supportsDeveloperRole: boolean;
   supportsReasoningEffort: boolean;
   supportsUsageInStreaming: boolean;
+  maxTokensField: "max_completion_tokens" | "max_tokens";
+  thinkingFormat: "openai" | "openrouter" | "zai";
   supportsStrictMode: boolean;
 };
 
@@ -50,6 +52,12 @@ export function resolveOpenAICompletionsCompatDefaults(
     isZai ||
     (isDefaultRoute &&
       isDefaultRouteProvider(input.provider, "cerebras", "chutes", "deepseek", "opencode", "xai"));
+  const isOpenRouterLike = input.provider === "openrouter" || endpointClass === "openrouter";
+  const usesMaxTokens =
+    endpointClass === "chutes-native" ||
+    endpointClass === "mistral-public" ||
+    knownProviderFamily === "mistral" ||
+    (isDefaultRoute && isDefaultRouteProvider(input.provider, "chutes"));
 
   return {
     supportsStore:
@@ -62,6 +70,8 @@ export function resolveOpenAICompletionsCompatDefaults(
       !usesExplicitProxyLikeEndpoint,
     supportsUsageInStreaming:
       !isNonStandard && (!usesConfiguredNonOpenAIEndpoint || supportsNativeStreamingUsageCompat),
+    maxTokensField: usesMaxTokens ? "max_tokens" : "max_completion_tokens",
+    thinkingFormat: isZai ? "zai" : isOpenRouterLike ? "openrouter" : "openai",
     supportsStrictMode: !isZai && !usesConfiguredNonOpenAIEndpoint,
   };
 }
diff --git a/src/agents/openai-transport-stream.ts b/src/agents/openai-transport-stream.ts
index 666bbf8f827..3440f2ec5a4 100644
--- a/src/agents/openai-transport-stream.ts
+++ b/src/agents/openai-transport-stream.ts
@@ -1346,11 +1346,6 @@ function detectCompat(model: OpenAIModeModel) {
     provider,
     ...capabilities,
   });
-  const isMistral =
-    capabilities.knownProviderFamily === "mistral" || endpointClass === "mistral-public";
-  const isZai = endpointClass === "zai-native" || (isDefaultRoute && provider === "zai");
-  const useMaxTokens =
-    endpointClass === "chutes-native" || (isDefaultRoute && provider === "chutes") || isMistral;
   const isGroq = endpointClass === "groq-native" || (isDefaultRoute && provider === "groq");
   const reasoningEffortMap: Record<string, string> =
     isGroq && model.id === "qwen/qwen3-32b"
@@ -1368,17 +1363,11 @@ function detectCompat(model: OpenAIModeModel) {
     supportsReasoningEffort: compatDefaults.supportsReasoningEffort,
     reasoningEffortMap,
     supportsUsageInStreaming: compatDefaults.supportsUsageInStreaming,
-    maxTokensField: useMaxTokens ? "max_tokens" : "max_completion_tokens",
+    maxTokensField: compatDefaults.maxTokensField,
     requiresToolResultName: false,
     requiresAssistantAfterToolResult: false,
     requiresThinkingAsText: false,
-    thinkingFormat: isZai
-      ? "zai"
-      : provider === "openrouter" ||
-          capabilities.endpointClass === "openrouter" ||
-          capabilities.attributionProvider === "openrouter"
-        ? "openrouter"
-        : "openai",
+    thinkingFormat: compatDefaults.thinkingFormat,
     openRouterRouting: {},
     vercelGatewayRouting: {},
     supportsStrictMode: compatDefaults.supportsStrictMode,