Where the governed streaming path adds latency
A governed streaming request passes through six stages. Every stage that runs before the first streamed byte can add to time-to-first-token, so each one needs a clear position in the path. Only the upstream model call is outside the proxy's control.
| Stage | Description | Position in the path |
|---|---|---|
| Connection handling | Accept the client connection and reuse upstream connections. | Before the model call |
| Authentication | Validate identity using cached, short-lived credentials. | Before the model call |
| Pre-request checks | Apply policy and inspect the prompt before the model call. | Before the model call |
| Upstream model call | Model latency, outside proxy control. | Model latency |
| Streamed response inspection | Evaluate chunks or windows as they pass through. | Incremental, while streaming |
| Audit logging | Record decisions and timings outside the blocking path. | Off the request path |
Which controls block the first token
Keep only the checks that must precede the model call in the blocking path:
- Authentication: validate identity using cached, short-lived credentials.
- A cached policy decision: apply policy without a fresh lookup on every request.
- Scoped request inspection: inspect the prompt before the model call, scoped by route and data class.
Everything else can run in parallel or after the first token. Output inspection happens incrementally as streamed bytes are forwarded without buffering, and audit logging moves off the request path onto a durable queue.
Measure proxy overhead separately from model latency
Measure proxy overhead as its own span so it is never confused with model latency. The upstream model call is outside proxy control, so a separate span for the proxy's own work shows what the governance layer contributes to time-to-first-token and what the model contributes.
Audit logging should record decisions and timings outside the blocking path, so the timing data needed for this comparison is captured without adding to the request.
Inspecting streamed output: chunk, window, or full response
Streamed response inspection can evaluate chunks or windows as they pass through, which allows streamed bytes to be forwarded without buffering. Inspecting output incrementally keeps the stream moving.
Evaluating the full response means holding output until it completes, which conflicts with forwarding bytes as they arrive. For that reason, incremental inspection is the approach this guide recommends for keeping time-to-first-token low.
Configuration techniques that protect TTFT
- Reuse upstream connections: Keep connections to model endpoints open so requests avoid repeated connection and TLS setup.
- Disable buffering on every hop: Check the proxy, load balancers, and any intermediate layers. Flush each server-sent event as it arrives rather than waiting for a full buffer.
- Cache identity and policy decisions locally: Use short expiry times and an explicit invalidation path so revocation and policy changes still take effect.
- Run independent checks in parallel: Authentication, policy retrieval, and different prompt detectors rarely depend on each other and need not run in sequence.
- Scope inline inspection by route and data class: Apply fast deterministic detectors inline and reserve slower analysis for asynchronous review or higher-risk routes.
- Decouple logging from the response: Write events to a durable queue and process them outside the request path.