> ## Documentation Index
> Fetch the complete documentation index at: https://docs.astrolabe.run/llms.txt
> Use this file to discover all available pages before exploring further.

# Customize Stacks

> Configure model boundaries, objectives, fallback, verification, budget, memory, and observability.

Custom stacks give your workspace explicit control over how Astrolabe Cloud routes requests.

Start by cloning a managed stack, then publish a custom version when the policy is ready.

## Boundaries

Boundaries decide which candidates are eligible before scoring.

Use them to configure:

* `allowedProviders`
* `blockedProviders`
* `allowedModels`
* `blockedModels`
* `requiredCapabilities`
* `dataPolicy`
* `retentionPolicy`
* `fallbackMustStayInPolicy`

If no candidate remains after boundaries are applied, the gateway returns `routing_policy_blocked` and does not call a provider.

## Objective

The objective tells Astrolabe what the stack optimizes for.

Key fields:

* `primary`: routing strategy such as lowest-cost passable model, fastest passable model, highest quality within budget, fixed priority order, or custom rules.
* `qualityTarget`: `draft`, `standard`, `high`, or `critical`.
* `costMode`: `lowest_passable`, `balanced`, `fastest_passable`, `premium`, or `fixed`.
* `latencySloMs`: optional latency target.
* `reliabilityTarget`: optional reliability target.
* `maxExpectedCostUsd`: optional per-request expected cost ceiling.

## Fallback

Fallback controls retry and escalation behavior.

Configure:

* whether fallback is enabled
* maximum attempts
* fallback mode
* trigger reasons such as provider errors, schema failures, or verifier low confidence
* categories that should never escalate

When `fallbackMustStayInPolicy` is enabled, fallback candidates must still satisfy stack boundaries.

## Verification

Verification controls post-response checks.

Modes include:

* `off`
* `auto`
* `light`
* `strict`
* `strong`

Use stricter verification for schema-heavy, high-stakes, customer-data, or external-action workflows. Use lighter verification for low-risk high-volume traffic.

## Budget

Budget settings help keep traffic inside workspace policy:

* monthly budget
* daily budget
* per-request maximum
* warning percentage
* hard-stop percentage

Prepaid workspace balance still applies to every request.

## Memory

Memory settings control what Astrolabe can learn from outcomes:

* workspace outcome learning
* user feedback learning
* raw prompt storage
* raw output storage
* fingerprint-only mode

For sensitive workloads, keep raw prompt and output storage disabled and use fingerprint-only memory.

## Observability

Observability controls response metadata and trace persistence:

* response headers
* inline metadata
* route trace persistence

Disable trace persistence only when your data policy requires it. The `x-astrolabe-cloud-request-id` header is still the best support handle.