diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index f42e14139f1e..3a5562884d91 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -1432,6 +1432,15 @@ export function schema(model: Provider.Model, schema: JSONSchema7): JSONSchema7
   }
   */
 
+  // Ensure `required` is always an array when `properties` is present.
+  // Strict JSON Schema validators (e.g. ajv used by some API gateways/proxies)
+  // reject schemas where `additionalProperties: false` is set but `required`
+  // is missing or null. This normalizes all object schemas to include an
+  // explicit (possibly empty) `required` array.
+  if (schema.type === "object" && schema.properties && !Array.isArray(schema.required)) {
+    schema.required = []
+  }
+
   if (model.api.npm === "@ai-sdk/openai" || model.api.npm === "@ai-sdk/azure") {
     schema = sanitizeOpenAISchema(schema) as JSONSchema7
     // Codex also applies lossy compaction above 4 KB; defer that until OpenCode needs the same schema budget.
diff --git a/packages/opencode/src/session/tools.ts b/packages/opencode/src/session/tools.ts
index 0f401c7562fa..59c7ad6cd020 100644
--- a/packages/opencode/src/session/tools.ts
+++ b/packages/opencode/src/session/tools.ts
@@ -150,6 +150,7 @@ export const resolve = Effect.fn("SessionTools.resolve")(function* (input: {
             },
           },
           additionalProperties: false,
+          required: [],
         }),
       ),
       execute(args, opts) {
@@ -233,6 +234,7 @@ export const resolve = Effect.fn("SessionTools.resolve")(function* (input: {
             },
           },
           additionalProperties: false,
+          required: [],
         }),
       ),
       execute(args, opts) {