SLO Tracking - Xerotier

Overview

Service Level Objectives (SLOs) define target performance for your inference endpoints. Xerotier provides two complementary SLO mechanisms:

SLO Management API -- Define SLO targets, track compliance over time, and view project-wide summaries through a full CRUD API.
Per-request SLO headers -- Pass latency targets on individual requests to hint routing preferences in real time.

SLO Management API

All paths are relative to your endpoint base URL: https://api.xerotier.ai/proj_ABC123/ENDPOINT_SLUG

Endpoints

Method	Path	Description
POST	/v1/slos	Create an SLO definition
GET	/v1/slos	List SLO definitions
GET	/v1/slos/{id}	Get an SLO definition
PUT	/v1/slos/{id}	Update an SLO definition
DELETE	/v1/slos/{id}	Delete an SLO definition
GET	/v1/slos/{id}/history	Get compliance history
POST	/v1/slos/{id}/calculate	Trigger manual calculation
GET	/v1/slos/summary	Get project SLO summary
GET	/v1/endpoints/{endpoint_id}/slos	List SLOs for an endpoint

Create SLO

POST /v1/slos

Parameter	Type	Description
namerequired	string	Human-readable name (1-128 ASCII printable characters).
descriptionoptional	string	Optional description (max 512 characters).
metricrequired	string	Metric to track. See Supported Metrics.
targetrequired	number	Target threshold value (must be positive).
comparisonrequired	string	Comparison operator. See Comparisons.
window_daysrequired	integer	Rolling evaluation window in days (1-90).
endpoint_idoptional	string	Endpoint UUID to scope the SLO. Omit for project-wide SLOs.

curl

                    curl -X POST https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos \
  -H "Authorization: Bearer xero_myproject_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "API Availability",
    "description": "99.9% availability for production API",
    "metric": "availability",
    "target": 99.9,
    "comparison": "greater_than_or_equal",
    "window_days": 30
  }'
                

Response

                        {
  "id": "00000000-1111-0000-1111-000000000000",
  "object": "slo",
  "name": "API Availability",
  "description": "99.9% availability for production API",
  "metric": "availability",
  "target": 99.9,
  "comparison": "greater_than_or_equal",
  "window_days": 30,
  "endpoint_id": null,
  "is_active": true,
  "latest_compliance": null,
  "created_at": 1709000000,
  "updated_at": 1709000000
}
                    

List SLOs

GET /v1/slos

Returns a paginated list of SLO definitions. Use limit and after for pagination.

curl

                    curl https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos?limit=10 \
  -H "Authorization: Bearer xero_myproject_your_api_key"
                

Get SLO

GET /v1/slos/{slo_id}

Returns the SLO definition with its latest compliance data.

curl

                    curl https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos/00000000-1111-0000-1111-000000000000 \
  -H "Authorization: Bearer xero_myproject_your_api_key"
                

Response (with compliance data)

                        {
  "id": "00000000-1111-0000-1111-000000000000",
  "object": "slo",
  "name": "API Availability",
  "metric": "availability",
  "target": 99.9,
  "comparison": "greater_than_or_equal",
  "window_days": 30,
  "is_active": true,
  "latest_compliance": {
    "measured_value": 99.95,
    "compliance_percentage": 100.0,
    "is_met": true,
    "total_requests": 150000,
    "conforming_requests": 150000,
    "calculated_at": 1709050000
  },
  "created_at": 1709000000,
  "updated_at": 1709000000
}
                    

Update SLO

PUT /v1/slos/{slo_id}

All fields are optional. Only provided fields are updated.

Parameter	Type	Description
nameoptional	string	Updated name.
descriptionoptional	string	Updated description (null to clear).
targetoptional	number	Updated target value.
comparisonoptional	string	Updated comparison operator.
window_daysoptional	integer	Updated window (1-90 days).
is_activeoptional	boolean	Enable or disable the SLO.
endpoint_idoptional	string	Updated endpoint scope (null for project-wide).

curl

                    curl -X PUT https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos/00000000-1111-0000-1111-000000000000 \
  -H "Authorization: Bearer xero_myproject_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "target": 99.95,
    "window_days": 7
  }'
                

Delete SLO

DELETE /v1/slos/{slo_id}

Permanently deletes the SLO definition and all associated history.

curl

                    curl -X DELETE https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos/00000000-1111-0000-1111-000000000000 \
  -H "Authorization: Bearer xero_myproject_your_api_key"
                

Get Compliance History

GET /v1/slos/{slo_id}/history

Returns a paginated list of compliance calculation entries for the SLO.

curl

                    curl https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos/00000000-1111-0000-1111-000000000000/history?limit=10 \
  -H "Authorization: Bearer xero_myproject_your_api_key"
                

Response

                        {
  "object": "list",
  "data": [
    {
      "id": "hist_abc123",
      "object": "slo.history",
      "slo_id": "00000000-1111-0000-1111-000000000000",
      "period_start": 1708900000,
      "period_end": 1709000000,
      "measured_value": 99.95,
      "total_requests": 150000,
      "conforming_requests": 150000,
      "compliance_percentage": 100.0,
      "is_met": true,
      "calculated_at": 1709000100
    }
  ],
  "first_id": "hist_abc123",
  "last_id": "hist_abc123",
  "has_more": false
}
                    

Trigger Calculation

POST /v1/slos/{slo_id}/calculate

Triggers an on-demand compliance calculation for the SLO and returns the result.

curl

                    curl -X POST https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos/00000000-1111-0000-1111-000000000000/calculate \
  -H "Authorization: Bearer xero_myproject_your_api_key"
                

Project Summary

GET /v1/slos/summary

Returns an overview of all active SLOs for the project with their current compliance status.

curl

                    curl https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos/summary \
  -H "Authorization: Bearer xero_myproject_your_api_key"
                

Response

                        {
  "object": "slo.summary",
  "total_active": 3,
  "total_met": 2,
  "total_not_met": 1,
  "total_unevaluated": 0,
  "slos": [
    {
      "id": "slo_1",
      "name": "API Availability",
      "metric": "availability",
      "target": 99.9,
      "status": "met",
      "compliance_percentage": 99.98,
      "measured_value": 99.98,
      "last_calculated_at": 1709050000
    },
    {
      "id": "slo_2",
      "name": "P95 Latency",
      "metric": "total_latency_ms",
      "target": 500,
      "status": "not_met",
      "compliance_percentage": 94.2,
      "measured_value": 520.0,
      "last_calculated_at": 1709050000
    }
  ]
}
                    

Limits

Max 50 SLO definitions per project.
Window range: 1-90 days.
Name length: 1-128 ASCII printable characters.
Description length: Max 512 characters.

Supported Metrics

Metric	Description	Unit
`ttft_ms`	Time to first token	milliseconds
`tpot_ms`	Time per output token	milliseconds
`total_latency_ms`	Total end-to-end request latency	milliseconds
`availability`	Percentage of successful requests	percent (0-100)
`error_rate`	Percentage of failed requests	percent (0-100)
`throughput_rps`	Average requests per second	requests/second

Comparison Operators

Comparison	Description	Typical Use
`less_than`	Metric must be less than target	Latency, error rate
`less_than_or_equal`	Metric must be at most target	Latency, error rate
`greater_than`	Metric must exceed target	Throughput
`greater_than_or_equal`	Metric must be at least target	Availability

Compliance Calculation

SLO compliance is measured as the percentage of requests within the evaluation window that meet the defined target:

compliance_percentage = (conforming_requests / total_requests) * 100

A request is "conforming" if the measured metric value satisfies the comparison operator against the target. For example, with metric=availability, target=99.9, comparison=greater_than_or_equal, the SLO is met when the measured availability is 99.9% or higher.

Compliance calculations run automatically on a periodic schedule. Use the POST /v1/slos/{id}/calculate endpoint to trigger an on-demand calculation.

SLO Request Headers

Include SLO targets as request headers on chat completion requests. These are optional hints -- they do not enforce hard limits or cause requests to fail if targets are missed.

Header	Type	Description
`X-SLO-TTFT-Ms`	integer	Target time-to-first-token in milliseconds (e.g., 500 for 500ms TTFT target).
`X-SLO-TPOT-Ms`	integer	Target time-per-output-token in milliseconds (e.g., 30 for 30ms per token).

You can send one or both headers. If neither is provided, the router uses its default routing strategy without SLO-aware adjustments. When these headers are present, the router prefers backends that are predicted to meet the specified latency targets. SLO headers do not guarantee that the target will be met -- they are best-effort hints. If no backend is predicted to meet the target, the router still selects the best available backend.

Examples

Create an Availability SLO

curl

                    curl -X POST https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos \
  -H "Authorization: Bearer xero_myproject_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Production Availability",
    "metric": "availability",
    "target": 99.9,
    "comparison": "greater_than_or_equal",
    "window_days": 30
  }'
                

Create a Latency SLO

curl

                    curl -X POST https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/slos \
  -H "Authorization: Bearer xero_myproject_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "P95 TTFT Target",
    "metric": "ttft_ms",
    "target": 500,
    "comparison": "less_than_or_equal",
    "window_days": 7
  }'
                

Per-Request SLO Headers

curl

                    curl https://api.xerotier.ai/proj_ABC123/my-endpoint/v1/chat/completions \
  -H "Authorization: Bearer xero_myproject_your_api_key" \
  -H "Content-Type: application/json" \
  -H "X-SLO-TTFT-Ms: 500" \
  -H "X-SLO-TPOT-Ms: 30" \
  -d '{
    "model": "llama-3.1-8b",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'
                

Python

                    import requests

base = "https://api.xerotier.ai/proj_ABC123/my-endpoint/v1"
headers = {"Authorization": "Bearer xero_myproject_your_api_key"}

# Create an SLO
slo = requests.post(f"{base}/slos", headers=headers, json={
    "name": "Chat Latency",
    "metric": "total_latency_ms",
    "target": 1000,
    "comparison": "less_than",
    "window_days": 7
}).json()
print(f"Created SLO: {slo['id']}")

# Check compliance summary
summary = requests.get(f"{base}/slos/summary", headers=headers).json()
for entry in summary["slos"]:
    print(f"{entry['name']}: {entry['status']} ({entry['compliance_percentage']}%)")

# Send a request with SLO headers
response = requests.post(
    f"{base}/chat/completions",
    headers={
        **headers,
        "Content-Type": "application/json",
        "X-SLO-TTFT-Ms": "500",
        "X-SLO-TPOT-Ms": "30",
    },
    json={
        "model": "llama-3.1-8b",
        "messages": [{"role": "user", "content": "Hello!"}],
    },
)
                

Node.js

                    const base = "https://api.xerotier.ai/proj_ABC123/my-endpoint/v1";
const headers = {
    "Authorization": "Bearer xero_myproject_your_api_key",
    "Content-Type": "application/json"
};

// Create an SLO
const sloResponse = await fetch(`${base}/slos`, {
    method: "POST",
    headers,
    body: JSON.stringify({
        name: "Chat Latency",
        metric: "total_latency_ms",
        target: 1000,
        comparison: "less_than",
        window_days: 7
    })
});
const slo = await sloResponse.json();
console.log(`Created SLO: ${slo.id}`);

// Check compliance summary
const summaryResponse = await fetch(`${base}/slos/summary`, { headers });
const summary = await summaryResponse.json();
for (const entry of summary.slos) {
    console.log(`${entry.name}: ${entry.status} (${entry.compliance_percentage}%)`);
}

// Send a request with SLO headers
const inferenceResponse = await fetch(`${base}/chat/completions`, {
    method: "POST",
    headers: {
        ...headers,
        "X-SLO-TTFT-Ms": "500",
        "X-SLO-TPOT-Ms": "30"
    },
    body: JSON.stringify({
        model: "llama-3.1-8b",
        messages: [{ role: "user", content: "Hello!" }]
    })
});
                