fix(provider): only set thinkingConfig for models with reasoning capability (#18283)

2 files changed, 73 insertions, 5 deletions

diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 05b9f031f..8298351ae 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -755,11 +755,13 @@ export namespace ProviderTransform {
     }
 
     if (input.model.api.npm === "@ai-sdk/google" || input.model.api.npm === "@ai-sdk/google-vertex") {
-      result["thinkingConfig"] = {
-        includeThoughts: true,
-      }
-      if (input.model.api.id.includes("gemini-3")) {
-        result["thinkingConfig"]["thinkingLevel"] = "high"
+      if (input.model.capabilities.reasoning) {
+        result["thinkingConfig"] = {
+          includeThoughts: true,
+        }
+        if (input.model.api.id.includes("gemini-3")) {
+          result["thinkingConfig"]["thinkingLevel"] = "high"
+        }
       }
     }
 
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 917d357ea..370edeed3 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -104,6 +104,72 @@ describe("ProviderTransform.options - setCacheKey", () => {
   })
 })
 
+describe("ProviderTransform.options - google thinkingConfig gating", () => {
+  const sessionID = "test-session-123"
+
+  const createGoogleModel = (reasoning: boolean, npm: "@ai-sdk/google" | "@ai-sdk/google-vertex") =>
+    ({
+      id: `${npm === "@ai-sdk/google" ? "google" : "google-vertex"}/gemini-2.0-flash`,
+      providerID: npm === "@ai-sdk/google" ? "google" : "google-vertex",
+      api: {
+        id: "gemini-2.0-flash",
+        url: npm === "@ai-sdk/google" ? "https://generativelanguage.googleapis.com" : "https://vertexai.googleapis.com",
+        npm,
+      },
+      name: "Gemini 2.0 Flash",
+      capabilities: {
+        temperature: true,
+        reasoning,
+        attachment: true,
+        toolcall: true,
+        input: { text: true, audio: false, image: true, video: false, pdf: true },
+        output: { text: true, audio: false, image: false, video: false, pdf: false },
+        interleaved: false,
+      },
+      cost: {
+        input: 0.001,
+        output: 0.002,
+        cache: { read: 0.0001, write: 0.0002 },
+      },
+      limit: {
+        context: 1_000_000,
+        output: 8192,
+      },
+      status: "active",
+      options: {},
+      headers: {},
+    }) as any
+
+  test("does not set thinkingConfig for google models without reasoning capability", () => {
+    const result = ProviderTransform.options({
+      model: createGoogleModel(false, "@ai-sdk/google"),
+      sessionID,
+      providerOptions: {},
+    })
+    expect(result.thinkingConfig).toBeUndefined()
+  })
+
+  test("sets thinkingConfig for google models with reasoning capability", () => {
+    const result = ProviderTransform.options({
+      model: createGoogleModel(true, "@ai-sdk/google"),
+      sessionID,
+      providerOptions: {},
+    })
+    expect(result.thinkingConfig).toEqual({
+      includeThoughts: true,
+    })
+  })
+
+  test("does not set thinkingConfig for vertex models without reasoning capability", () => {
+    const result = ProviderTransform.options({
+      model: createGoogleModel(false, "@ai-sdk/google-vertex"),
+      sessionID,
+      providerOptions: {},
+    })
+    expect(result.thinkingConfig).toBeUndefined()
+  })
+})
+
 describe("ProviderTransform.options - gpt-5 textVerbosity", () => {
   const sessionID = "test-session-123"