diff --git a/src/cloudcode/message-handler.js b/src/cloudcode/message-handler.js
index 312a974..56de18a 100644
--- a/src/cloudcode/message-handler.js
+++ b/src/cloudcode/message-handler.js
@@ -396,6 +396,13 @@ export async function sendMessage(anthropicRequest, accountManager, fallbackEnab
                                 throw new Error(`CAPACITY_EXHAUSTED: ${errorText}`);
                             }
 
+                            // 400 errors are client errors - fail immediately, don't retry or switch accounts
+                            // Examples: token limit exceeded, invalid schema, malformed request
+                            if (response.status === 400) {
+                                logger.error(`[CloudCode] Invalid request (400): ${errorText.substring(0, 200)}`);
+                                throw new Error(`invalid_request_error: ${errorText}`);
+                            }
+
                             lastError = new Error(`API error ${response.status}: ${errorText}`);
                             // Try next endpoint for 403/404/5xx errors (matches opencode-antigravity-auth behavior)
                             if (response.status === 403 || response.status === 404) {
@@ -430,6 +437,10 @@ export async function sendMessage(anthropicRequest, accountManager, fallbackEnab
                     if (isRateLimitError(endpointError)) {
                         throw endpointError; // Re-throw to trigger account switch
                     }
+                    // 400 errors are client errors - re-throw immediately, don't retry
+                    if (endpointError.message?.includes('400')) {
+                        throw endpointError;
+                    }
                     logger.warn(`[CloudCode] Error at ${endpoint}:`, endpointError.message);
                     lastError = endpointError;
                     endpointIndex++;
diff --git a/src/cloudcode/streaming-handler.js b/src/cloudcode/streaming-handler.js
index d32c363..dbe043d 100644
--- a/src/cloudcode/streaming-handler.js
+++ b/src/cloudcode/streaming-handler.js
@@ -389,6 +389,13 @@ export async function* sendMessageStream(anthropicRequest, accountManager, fallb
                             throw new Error(`CAPACITY_EXHAUSTED: ${errorText}`);
                         }
 
+                        // 400 errors are client errors - fail immediately, don't retry or switch accounts
+                        // Examples: token limit exceeded, invalid schema, malformed request
+                        if (response.status === 400) {
+                            logger.error(`[CloudCode] Invalid request (400): ${errorText.substring(0, 200)}`);
+                            throw new Error(`invalid_request_error: ${errorText}`);
+                        }
+
                         lastError = new Error(`API error ${response.status}: ${errorText}`);
 
                         // Try next endpoint for 403/404/5xx errors (matches opencode-antigravity-auth behavior)
@@ -488,6 +495,10 @@ export async function* sendMessageStream(anthropicRequest, accountManager, fallb
                     if (isEmptyResponseError(endpointError)) {
                         throw endpointError;
                     }
+                    // 400 errors are client errors - re-throw immediately, don't retry
+                    if (endpointError.message?.includes('400')) {
+                        throw endpointError;
+                    }
                     logger.warn(`[CloudCode] Stream error at ${endpoint}:`, endpointError.message);
                     lastError = endpointError;
                     endpointIndex++;