diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index 9b01eae9e9b..e111e81344f 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -418,11 +418,26 @@ export namespace Provider {
             "HTTP-Referer": "https://opencode.ai/",
             "X-Title": "opencode",
           },
-          // Custom fetch to strip Authorization header - AI Gateway uses cf-aig-authorization instead
-          // Sending Authorization header with invalid value causes auth errors
+          // Custom fetch to handle parameter transformation and auth
           fetch: async (input: RequestInfo | URL, init?: RequestInit) => {
             const headers = new Headers(init?.headers)
+            // Strip Authorization header - AI Gateway uses cf-aig-authorization instead
             headers.delete("Authorization")
+
+            // Transform max_tokens to max_completion_tokens for newer models
+            if (init?.body && init.method === "POST") {
+              try {
+                const body = JSON.parse(init.body as string)
+                if (body.max_tokens !== undefined && !body.max_completion_tokens) {
+                  body.max_completion_tokens = body.max_tokens
+                  delete body.max_tokens
+                  init = { ...init, body: JSON.stringify(body) }
+                }
+              } catch (e) {
+                // If body parsing fails, continue with original request
+              }
+            }
+
             return fetch(input, { ...init, headers })
           },
         },