Metrics & OpenTelemetry

Scion provides built-in telemetry collection via sciontool, which runs as the init process in agent containers. The telemetry pipeline acts as an OTLP Forwarder: it receives data from agents locally and forwards it to a central cloud observability backend.

Telemetry Flow

1. Agent (The Source): Emits OTLP data (traces/metrics) or harness hook events.
2. sciontool (The Forwarder):
   • Receives OTLP via gRPC (port 4317) or HTTP (port 4318).
   • Normalizes harness hooks into standard OTLP spans.
   • Applies privacy filters (redaction/hashing).
3. Cloud Backend (The Destination): Receives the processed telemetry from sciontool.

Configuration

Telemetry is configured through settings.yaml (for global and grove-level defaults) and scion-agent.yaml (for per-template and per-agent overrides). Environment variables provide the highest-priority override.

Configuration Hierarchy

Telemetry settings resolve across scopes using last-write-wins semantics:

1. Global settings (~/.scion/settings.yaml) — Organization-wide defaults.
2. Grove settings (.scion/settings.yaml) — Project-level overrides.
3. Template config (scion-agent.yaml in template) — Role-specific overrides.
4. Agent config (scion-agent.yaml in agent home) — Per-agent overrides.
5. Environment variables (SCION_TELEMETRY_*, SCION_OTEL_*) — Highest priority.

At each scope, only the fields you specify are overridden; unset fields inherit from the previous scope.

Settings File Configuration

The telemetry block can appear in any settings.yaml (global or grove) or scion-agent.yaml (template or agent):

# In settings.yaml or scion-agent.yaml
telemetry:
  enabled: true

  cloud:
    enabled: true
    endpoint: "monitoring.googleapis.com:443"
    protocol: grpc
    headers:
      Authorization: "Bearer ${OTEL_API_KEY}"
    tls:
      enabled: true
      insecure_skip_verify: false
    batch:
      max_size: 512
      timeout: "5s"

  hub:
    enabled: true
    report_interval: "30s"

  local:
    enabled: false
    file: ""
    console: false

  filter:
    enabled: true
    respect_debug_mode: true
    events:
      include: []
      exclude:
        - "agent.user.prompt"
    attributes:
      redact:
        - "prompt"
        - "user.email"
        - "tool_output"
      hash:
        - "session_id"
    sampling:
      default: 1.0
      rates: {}

  resource:
    service.name: "scion-agent"

See the Orchestrator Settings Reference for the full field reference.

Environment Variable Overrides

Environment variables override any settings file value and are the most convenient option for CI or hosted deployments.

Variable	Settings Path	Default	Description
SCION_TELEMETRY_ENABLED	telemetry.enabled	true	Enable/disable collection entirely
SCION_TELEMETRY_CLOUD_ENABLED	telemetry.cloud.enabled	true	Enable forwarding to cloud backend
SCION_OTEL_ENDPOINT	telemetry.cloud.endpoint	(required)	Cloud OTLP endpoint URL
SCION_OTEL_PROTOCOL	telemetry.cloud.protocol	grpc	Protocol: grpc or http
SCION_OTEL_INSECURE	telemetry.cloud.tls.insecure_skip_verify	false	Skip TLS verification (dev only)
SCION_TELEMETRY_HUB_ENABLED	telemetry.hub.enabled	true	Enable Hub reporting
SCION_TELEMETRY_DEBUG	telemetry.local.enabled	false	Enable local debug output
SCION_GCP_PROJECT_ID	—	(auto)	GCP project ID for Google Cloud backends

Local Receiver Settings (For Agents)

These settings control the ports where sciontool listens for data from the agent processes inside the container.

Variable	Default	Description
SCION_OTEL_GRPC_PORT	4317	Local gRPC receiver port
SCION_OTEL_HTTP_PORT	4318	Local HTTP receiver port

Google Cloud Setup (Recommended)

When deploying on Google Cloud, sciontool can forward directly to Cloud Trace and Cloud Logging using the standard OTLP endpoint.

1. Configure the Forwarder

Set these environment variables in your Hub settings (Grove or Broker level):

# Direct OTLP ingestion for Google Cloud
export SCION_OTEL_ENDPOINT="monitoring.googleapis.com:443"
export SCION_OTEL_PROTOCOL="grpc"
export SCION_GCP_PROJECT_ID="your-project-id"

2. Configure the Agent (Native OTel)

If your agent harness supports native OpenTelemetry (e.g., opencode), configure it to point to the sciontool forwarder running on localhost:

# Tell the agent to send to sciontool
export OTEL_EXPORTER_OTLP_ENDPOINT="localhost:4317"

Note: Most standard OTel SDKs default to localhost:4317, so explicit configuration may not be required.

3. IAM Permissions

Ensure the environment where the agent container runs (GKE Pod, Cloud Run, etc.) has a service account with:

• roles/logging.logWriter
• roles/cloudtrace.agent
• roles/monitoring.metricWriter

Native Metrics Pipeline

Scion includes a native OTel metrics pipeline that captures operational data from agent sessions. This data is recorded as counters and histograms, providing a time-series view of agent performance.

To enable harness-aware telemetry, Scion automatically injects SCION_HARNESS and SCION_MODEL environment variables into all agent containers.

Enriched Resource Attributes

All metrics and traces emitted by Scion are enriched with context-aware OpenTelemetry resource attributes to allow for precise filtering and aggregation in your cloud backend:

• scion.harness: The type of harness running the agent (e.g., gemini, claude, codex).
• scion.model: The specific LLM model being used.
• scion.broker: The ID of the Runtime Broker executing the agent.
• grove_id: The ID of the agent’s parent grove.

Automated Metrics Collection

When harness events occur (via hooks), sciontool automatically records the following metrics:

Metric	Type	Unit	Description
gen_ai.tokens.input	Counter	tokens	Number of input tokens processed
gen_ai.tokens.output	Counter	tokens	Number of output tokens generated
gen_ai.tokens.cached	Counter	tokens	Number of tokens retrieved from cache
agent.tool.calls	Counter	calls	Total number of tool executions
agent.tool.duration	Histogram	ms	Latency of tool executions
agent.session.count	Counter	sessions	Total number of agent sessions
gen_ai.api.calls	Counter	calls	Total number of LLM API requests
gen_ai.api.duration	Histogram	ms	Latency of LLM API requests

(Note: The Codex harness has been expanded to capture comprehensive telemetry including tool usage, detailed tool input/output, and granular token counts for input, output, and cached tokens).

Correlated Logs

For every significant lifecycle event (session start/end, tool use, model call), sciontool emits an OTel log record that is automatically correlated with the active trace. This means when viewing a trace waterfall in your observability backend (like Google Cloud Trace), you can click directly through to the specific logs associated with each span.

Hub Infrastructure Metrics

The Scion Hub maintains internal operational metrics for infrastructure monitoring. These are available via the /api/v1/admin/metrics endpoint (requires hub:admin role) and can be exported to standard monitoring tools.

GCP Token Metrics

With the introduction of GCP Identity emulation, the Hub tracks the health and performance of the token brokering pipeline:

Metric	Description
accessTokenRequests	Total number of GCP Access Token requests from agents.
accessTokenSuccesses	Number of successfully brokered access tokens.
accessTokenFailures	Number of failed access token requests (e.g., IAM permission errors).
idTokenRequests	Total number of GCP Identity Token requests.
rateLimitRejections	Number of token requests rejected due to per-agent rate limiting.
iamLatencyP50Ms	Median latency of IAM API calls to Google Cloud.
iamLatencyP95Ms	95th percentile latency of IAM API calls.

Broker Authentication Metrics

Monitors the security and connectivity of Runtime Brokers:

• authAttempts: Total broker authentication attempts.
• connectedBrokers: Current number of active Runtime Brokers connected to the Hub.
• dispatchFailures: Number of failed agent dispatch commands to brokers.

Privacy Filtering

By default, sciontool excludes agent.user.prompt events to protect user privacy. Filtering is configured via the telemetry.filter block in settings.yaml or scion-agent.yaml, or via environment variables.

Via Settings File

telemetry:
  filter:
    events:
      exclude:
        - "agent.user.prompt"
        - "agent.tool.result"
    attributes:
      redact:
        - "prompt"
        - "user.email"
        - "tool_output"
      hash:
        - "session_id"
    sampling:
      default: 1.0
      rates:
        "agent.tool.call": 0.5

Via Environment Variables

# Exclude multiple event types
export SCION_TELEMETRY_FILTER_EXCLUDE="agent.user.prompt,agent.tool.result"

# Only forward specific event types
export SCION_TELEMETRY_FILTER_INCLUDE="agent.session.start,agent.session.end,agent.tool.call"

Attribute Redaction

Beyond event filtering, sciontool provides field-level attribute redaction for sensitive data. This allows telemetry to flow while protecting specific values.

Redacted Fields

Redacted fields have their values replaced with [REDACTED]:

# Default redacted fields
export SCION_TELEMETRY_REDACT="prompt,user.email,tool_output,tool_input"

Hashed Fields

Hashed fields are replaced with their SHA256 hash, allowing correlation without exposing the original value:

# Default hashed fields
export SCION_TELEMETRY_HASH="session_id"

Hook-to-Span Conversion

Harness hook events are automatically converted to OTLP spans:

Hook Event	Span Name	Attributes
session-start	agent.session.start	session_id, source
session-end	agent.session.end	session_id, reason, tokens_*, duration_ms
tool-start	agent.tool.call	tool_name, tool_input
tool-end	agent.tool.result	tool_name, success, duration_ms
prompt-submit	agent.user.prompt	prompt
model-start	gen_ai.api.request	model
model-end	gen_ai.api.response	success

Session Metrics (Gemini)

For Gemini CLI agents, session-end events include aggregated metrics from the session file:

• Token counts: tokens_input, tokens_output, tokens_cached
• Session info: turn_count, duration_ms, model
• Per-tool statistics: tool.<name>.calls, tool.<name>.success, tool.<name>.errors

Session files are automatically parsed from ~/.gemini/sessions/.

Implementation Details

The telemetry pipeline is implemented in pkg/sciontool/telemetry/:

• config.go - Configuration loading from environment variables
• filter.go - Event type filtering (include/exclude) and attribute redaction
• exporter.go - Cloud OTLP exporter (gRPC and HTTP)
• receiver.go - OTLP gRPC/HTTP receiver
• pipeline.go - Main orchestration (Start/Stop lifecycle)

Hook-to-span conversion is in pkg/sciontool/hooks/handlers/:

• telemetry.go - TelemetryHandler for converting hooks to spans
• Session parsing in pkg/sciontool/hooks/session/parser.go

The pipeline is integrated into the init command (cmd/sciontool/commands/init.go) and starts after user setup, before lifecycle hooks.