diff --git a/apps/webapp/app/routes/realtime.v1.streams.$runId.$streamId.ts b/apps/webapp/app/routes/realtime.v1.streams.$runId.$streamId.ts
index 44d7858596..822c10a810 100644
--- a/apps/webapp/app/routes/realtime.v1.streams.$runId.$streamId.ts
+++ b/apps/webapp/app/routes/realtime.v1.streams.$runId.$streamId.ts
@@ -1,13 +1,79 @@
+import { type ActionFunctionArgs } from "@remix-run/server-runtime";
 import { z } from "zod";
 import { $replica } from "~/db.server";
 import { getRealtimeStreamInstance } from "~/services/realtime/v1StreamsGlobal.server";
 import { createLoaderApiRoute } from "~/services/routeBuilders/apiBuilder.server";
+import { AuthenticatedEnvironment } from "~/services/apiAuth.server";
 
 const ParamsSchema = z.object({
   runId: z.string(),
   streamId: z.string(),
 });
 
+// Plain action for backwards compatibility with older clients that don't send auth headers
+export async function action({ request, params }: ActionFunctionArgs) {
+  const parsedParams = ParamsSchema.safeParse(params);
+
+  if (!parsedParams.success) {
+    return new Response("Invalid parameters", { status: 400 });
+  }
+
+  const { runId, streamId } = parsedParams.data;
+
+  // Look up the run without environment scoping for backwards compatibility
+  const run = await $replica.taskRun.findFirst({
+    where: {
+      friendlyId: runId,
+    },
+    select: {
+      id: true,
+      friendlyId: true,
+      runtimeEnvironment: {
+        include: {
+          project: true,
+          organization: true,
+          orgMember: true,
+        },
+      },
+    },
+  });
+
+  if (!run) {
+    return new Response("Run not found", { status: 404 });
+  }
+
+  // Extract client ID from header, default to "default" if not provided
+  const clientId = request.headers.get("X-Client-Id") || "default";
+  const streamVersion = request.headers.get("X-Stream-Version") || "v1";
+
+  if (!request.body) {
+    return new Response("No body provided", { status: 400 });
+  }
+
+  const resumeFromChunk = request.headers.get("X-Resume-From-Chunk");
+  let resumeFromChunkNumber: number | undefined = undefined;
+  if (resumeFromChunk) {
+    const parsed = parseInt(resumeFromChunk, 10);
+    if (isNaN(parsed) || parsed < 0) {
+      return new Response(`Invalid X-Resume-From-Chunk header value: ${resumeFromChunk}`, {
+        status: 400,
+      });
+    }
+    resumeFromChunkNumber = parsed;
+  }
+
+  // The runtimeEnvironment from the run is already in the correct shape for AuthenticatedEnvironment
+  const realtimeStream = getRealtimeStreamInstance(run.runtimeEnvironment, streamVersion);
+
+  return realtimeStream.ingestData(
+    request.body,
+    run.friendlyId,
+    streamId,
+    clientId,
+    resumeFromChunkNumber
+  );
+}
+
 export const loader = createLoaderApiRoute(
   {
     params: ParamsSchema,