diff --git a/src/gateway/protocol/schema.ts b/src/gateway/protocol/schema.ts
index e4515c157..a76734337 100644
--- a/src/gateway/protocol/schema.ts
+++ b/src/gateway/protocol/schema.ts
@@ -1,6 +1,5 @@
 import { type Static, type TSchema, Type } from "@sinclair/typebox";
 import { SESSION_LABEL_MAX_LENGTH } from "../../sessions/session-label.js";
-import { GATEWAY_AGENT_PROVIDER_VALUES } from "../../utils/message-provider.js";
 
 const NonEmptyString = Type.String({ minLength: 1 });
 const SessionLabelString = Type.String({
@@ -8,10 +7,6 @@ const SessionLabelString = Type.String({
   maxLength: SESSION_LABEL_MAX_LENGTH,
 });
 
-const AgentProviderSchema = Type.Union(
-  GATEWAY_AGENT_PROVIDER_VALUES.map((provider) => Type.Literal(provider)),
-);
-
 export const PresenceEntrySchema = Type.Object(
   {
     host: Type.Optional(NonEmptyString),
@@ -230,7 +225,7 @@ export const AgentParamsSchema = Type.Object(
     sessionKey: Type.Optional(Type.String()),
     thinking: Type.Optional(Type.String()),
     deliver: Type.Optional(Type.Boolean()),
-    provider: Type.Optional(AgentProviderSchema),
+    provider: Type.Optional(Type.String()),
     timeout: Type.Optional(Type.Integer({ minimum: 0 })),
     lane: Type.Optional(Type.String()),
     extraSystemPrompt: Type.Optional(Type.String()),
diff --git a/src/gateway/server-methods/agent.ts b/src/gateway/server-methods/agent.ts
index d54023a3f..7b605106a 100644
--- a/src/gateway/server-methods/agent.ts
+++ b/src/gateway/server-methods/agent.ts
@@ -70,6 +70,26 @@ export const agentHandlers: GatewayRequestHandlers = {
       return;
     }
     const message = request.message.trim();
+    const rawProvider =
+      typeof request.provider === "string" ? request.provider.trim() : "";
+    if (rawProvider) {
+      const normalized = normalizeMessageProvider(rawProvider);
+      if (
+        normalized &&
+        normalized !== "last" &&
+        !isGatewayMessageProvider(normalized)
+      ) {
+        respond(
+          false,
+          undefined,
+          errorShape(
+            ErrorCodes.INVALID_REQUEST,
+            `invalid agent params: unknown provider: ${normalized}`,
+          ),
+        );
+        return;
+      }
+    }
 
     const requestedSessionKey =
       typeof request.sessionKey === "string" && request.sessionKey.trim()