How to fix webhook replies arriving too late for the LLM processing in n8n?

The fix is to let the webhook return its HTTP response immediately and move the heavy LLM work into a background branch. In practice, you split the workflow into two parts: the Webhook node gives a fast reply (like “ok”) using Respond to Webhook, and the LLM processing runs after that response is already sent. This avoids timeouts because the sender no longer waits for the LLM to finish.

 

Why the webhook replies arrive too late

 

n8n Webhook nodes hold the HTTP connection open until the workflow either:

• Sends a reply using a Respond to Webhook node
• Reaches the Webhook node's own built‑in response (if Output mode = Respond)

LLM calls often take several seconds. If you don't respond early, the caller (frontend, bot, API, whatever) times out before n8n finishes the LLM request. This is why replies arrive “too late.” It’s not that the LLM is slow — it’s that the webhook tries to wait for it.

 

The production‑grade fix: Early response + background processing

 

You want the webhook to close fast. That means:

• Webhook node receives the request
• You send an immediate reply with a Respond to Webhook node
• The rest of your workflow (LLM, API calls, database writes, etc.) runs after the response has been sent

This lets your workflow keep working in the background even though the caller already got its OK.

 

How to implement this in n8n

 

The cleanest pattern is to put Respond to Webhook as the first thing after the Webhook node, then branch the expensive work.

{
  "webhook_reply": "ok"
}

Example layout:

• Webhook Trigger
• Respond to Webhook (fast “ok”)
• Split in Two (or a simple connection): one branch ends here, the other continues to the LLM call
• LLM processing
• Store result / send message back to user via whatever channel you use

This pattern guarantees the webhook response is not delayed by the LLM call.

 

Alternative approach: Two separate workflows

 

If you want the cleanest architecture (especially for production), you can split it into two workflows:

• Workflow A: Handles the Webhook, responds immediately, writes the incoming data into a queue (database row, Redis, n8n Execution Trigger call, etc.)
• Workflow B: Triggered separately, processes the data via the LLM

This isolates the “fast reply” logic from the “slow LLM work,” which is often easier to maintain and scale.

 

Practical tips from real deployments

 

• Webhook senders (frontends, Slack, Telegram, custom apps) often require a reply within a few seconds. Never block them on LLM calls.
• If your LLM call can take long (10–60s), set Continue On Fail and better error handling so the background work doesn't kill the whole workflow.
• Use Set or Function nodes early to cache incoming useful data before sending the webhook reply — after the response is sent, the original request object may not be retrievable.

 

Summary in one sentence

 

To fix late webhook replies in n8n, respond immediately using a Respond to Webhook node and push all heavy LLM processing into a separate branch or workflow so the HTTP connection doesn’t wait for the LLM to finish.