add comment to v1 SDKs in V3

pages/docs/deployment/v3.mdx

@@ -8,6 +8,12 @@ Langfuse V3 is currently in development, see this [GitHub Discussion thread](htt
 
 This document summarizes changes compared to v2 with regards to self-hosted deployments. While v3 is not released, these changes are unstable and can change.
 
+## SDK compatibility
+
+Langfuse V3 will not be compatible with JS and Python SDKs versions below 2.0.0. The 1.x.x SDKs use deprecated APIs for inserting tracing data into Langfuse. These APIs depend on synchronous event processing and return the final database state of an object via the API. As Langfuse scales, we now use a queue to process events asynchronously, meaning the final state of an object is not immediately available via the API.
+
+If you are using the 1.x.x SDKs, you must upgrade to the 2.x.x SDKs to use Langfuse V3. You can find the updated SDKs here: [Python](https://pypi.org/project/langfuse/), [JS](https://www.npmjs.com/package/langfuse).
+
 ## Event Backups in Cloud Storage
 
 In addition to storing events in the database, you may want to store a backup of all raw incoming events in a cloud storage bucket.