Traffic Model

System Prompts

System prompt injection is route-level prompt assembly. Arc builds the final messages array server-side before forwarding the request.

Injection Bypass

Injection Behavior

If a route has a system prompt configured, Arc prepends it to the messages array as a normal system message. The upstream provider sees the final assembled array, not a special Arc-specific header.

json

// Request from your application
{
  "messages": [
    { "role": "user", "content": "Summarize this contract." }
  ]
}

// Final messages forwarded by Arc
[
  { "role": "system", "content": "Summarize in concise legal bullet points." },
  { "role": "user", "content": "Summarize this contract." }
]

Bypass Header

To opt out for a single request, pass X-Arc-No-Inject with 1, true, or yes.

http

X-Arc-No-Inject: 1

Workflows And Traces

Memory