diff --git a/package.json b/package.json
index 99d8495..dc72ec3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "@requesty/ai-sdk",
-    "version": "3.3.1",
+    "version": "3.4.0",
     "license": "Apache-2.0",
     "sideEffects": false,
     "main": "./dist/index.js",
diff --git a/src/usage/schema.ts b/src/usage/schema.ts
index efd9b99..6d1b3cb 100644
--- a/src/usage/schema.ts
+++ b/src/usage/schema.ts
@@ -2,15 +2,15 @@ import z from 'zod'
 
 export const RequestyUsageSchema = z
     .object({
-        prompt_tokens: z.number().optional(),
-        completion_tokens: z.number().optional(),
-        total_tokens: z.number().optional(),
+        prompt_tokens: z.number().nonnegative().optional(),
+        completion_tokens: z.number().nonnegative().optional(),
+        total_tokens: z.number().nonnegative().optional(),
         prompt_tokens_details: z
             .object({
-                caching_tokens: z.number().optional(),
-                cached_tokens: z.number().optional(),
+                caching_tokens: z.number().nonnegative().optional(),
+                cached_tokens: z.number().nonnegative().optional(),
             })
             .optional(),
-        cost: z.number().positive().optional(),
+        cost: z.number().nonnegative().optional(),
     })
     .optional()