diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 28e8d97ab6d..eafe382aba9 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -621,6 +621,35 @@ export namespace ProviderTransform {
     }
     */
 
+    // Ensure 'required' is always an array for object types to satisfy strict backends (e.g., SGLang)
+    const ensureRequiredField = (obj: any): any => {
+      if (obj === null || typeof obj !== "object") {
+        return obj
+      }
+
+      if (Array.isArray(obj)) {
+        return obj.map(ensureRequiredField)
+      }
+
+      const result: any = {}
+      for (const [key, value] of Object.entries(obj)) {
+        if (typeof value === "object" && value !== null) {
+          result[key] = ensureRequiredField(value)
+        } else {
+          result[key] = value
+        }
+      }
+
+      // Add required: [] for object types that don't have it
+      if (result.type === "object" && !result.required) {
+        result.required = []
+      }
+
+      return result
+    }
+
+    schema = ensureRequiredField(schema)
+
     // Convert integer enums to string enums for Google/Gemini
     if (model.providerID === "google" || model.api.id.includes("gemini")) {
       const sanitizeGemini = (obj: any): any => {
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 32b1ecb2444..2c2e59a93cb 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -167,6 +167,106 @@ describe("ProviderTransform.maxOutputTokens", () => {
   })
 })
 
+describe("ProviderTransform.schema - required field for strict backends", () => {
+  const genericModel = {
+    providerID: "openai-compatible",
+    api: {
+      id: "custom-model",
+    },
+  } as any
+
+  test("adds required: [] to empty object schemas", () => {
+    const schema = {
+      type: "object",
+      properties: {},
+    } as any
+
+    const result = ProviderTransform.schema(genericModel, schema) as any
+
+    expect(result.required).toEqual([])
+  })
+
+  test("preserves existing required field", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        name: { type: "string" },
+      },
+      required: ["name"],
+    } as any
+
+    const result = ProviderTransform.schema(genericModel, schema) as any
+
+    expect(result.required).toEqual(["name"])
+  })
+
+  test("adds required: [] to nested object schemas", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        nested: {
+          type: "object",
+          properties: {},
+        },
+      },
+    } as any
+
+    const result = ProviderTransform.schema(genericModel, schema) as any
+
+    expect(result.required).toEqual([])
+    expect(result.properties.nested.required).toEqual([])
+  })
+
+  test("handles deeply nested object schemas", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        level1: {
+          type: "object",
+          properties: {
+            level2: {
+              type: "object",
+              properties: {
+                value: { type: "string" },
+              },
+            },
+          },
+        },
+      },
+    } as any
+
+    const result = ProviderTransform.schema(genericModel, schema) as any
+
+    expect(result.required).toEqual([])
+    expect(result.properties.level1.required).toEqual([])
+    expect(result.properties.level1.properties.level2.required).toEqual([])
+  })
+
+  test("handles array of objects", () => {
+    const schema = {
+      type: "array",
+      items: {
+        type: "object",
+        properties: {},
+      },
+    } as any
+
+    const result = ProviderTransform.schema(genericModel, schema) as any
+
+    expect(result.items.required).toEqual([])
+  })
+
+  test("does not add required to non-object types", () => {
+    const schema = {
+      type: "string",
+    } as any
+
+    const result = ProviderTransform.schema(genericModel, schema) as any
+
+    expect(result.required).toBeUndefined()
+  })
+})
+
 describe("ProviderTransform.schema - gemini array items", () => {
   test("adds missing items for array properties", () => {
     const geminiModel = {