MXC Schema Version Differences: Comparing 0.5.0-alpha, 0.6.0-alpha, and 0.7.0-dev

The MXC configuration schema evolved from 0.5.0-alpha's introduction of process abstraction through 0.6.0-alpha's security-hardened network defaults to 0.7.0-dev's experimental backend support, with each release introducing structural changes to containment models, fallback controls, and extensibility mechanisms.

The microsoft/mxc repository defines a JSON-based configuration format that orchestrates container-execution backends across heterogeneous platforms. Understanding MXC schema version differences is critical for migrating configurations between releases and leveraging platform-specific containment capabilities as the SDK matures from alpha stability toward production-ready orchestration.

Version 0.5.0-alpha: Process Abstraction Foundation

Released as a transitional milestone, schema 0.5.0-alpha introduces the abstract process containment intent that decouples configuration authors from platform-specific backend implementations. According to schemas/stable/mxc-config.schema.0.5.0-alpha.json, this version adds the processContainer block as the canonical replacement for the legacy appContainer section while maintaining backward compatibility aliases.

Key Architectural Changes

Abstract Process Containment: The schema introduces the "containment": "process" value, which the SDK resolves at runtime to concrete backends via sdk/src/platform.ts, rather than requiring explicit backend selection as in earlier versions.

ProcessContainer Alias: Windows-specific UI and privilege settings migrate from appContainer to processContainer, establishing the pattern where platform-specific containers nest under their respective backend names while sharing common process configuration.

Version 0.6.0-alpha: Security-First Stable Release

Schema 0.6.0-alpha represents a hardening release defined in schemas/stable/mxc-config.schema.0.6.0-alpha.json, flipping the default security posture from permissive to restrictive and introducing explicit fallback controls.

Network Security Posture

The network.defaultPolicy field changes its default from "allow" to "block", enforcing deny-by-default networking that aligns with modern zero-trust principles. Configuration authors must now explicitly whitelist hosts via allowedHosts arrays rather than relying on implicit outbound access.

Fallback Control Mechanism

The new fallback top-level block provides opt-out controls for host-modifying fallback behaviors. Specifically, fallback.allowDaclMutation controls Tier-3 fallbacks that mutate host ACLs, which were previously implicit and uncontrollable in earlier schemas.

UI Policy Separation

A dedicated top-level ui block decouples interface constraints from backend-specific configuration, enabling cross-platform UI policies. While processContainer.ui retains Windows-specific settings, the abstract ui object provides portable clipboard, display, and input controls.

Version 0.7.0-dev: Experimental Backend Expansion

The development schema schemas/dev/mxc-config.schema.0.7.0-dev.json introduces a namespaced mechanism for unstable backend support, isolating experimental features from the stable configuration surface.

Experimental Namespace

The experimental top-level block contains backend-specific settings for platforms still in development. This includes windows_sandbox, wslc, microvm, macos_sandbox, isolation_session, and hyperlight backends, each with their own typed configuration objects that remain invisible to stable schema validation.

Extended Backend Support

Beyond stable backends (processcontainer, bubblewrap, lxc), 0.7.0-dev recognizes experimental containment mechanisms. For example, the wslc backend accepts cpuCount, memoryMb, and gpu parameters within its experimental namespace, allowing resource tuning for WSL-Container workloads without polluting the stable schema.

Configuration Examples by Version

0.5.0-alpha Configuration

The following example demonstrates the transition to process abstraction and the new processContainer block:

{
  "version": "0.5.0-alpha",
  "containment": "process",
  "process": { "commandLine": "python script.py" },
  "processContainer": {
    "leastPrivilege": true,
    "capabilities": ["internetClient"]
  },
  "filesystem": { "readwritePaths": ["/tmp"] },
  "network": { "defaultPolicy": "allow" }
}

Notice the abstract containment value and the migration from appContainer to processContainer.

0.6.0-alpha Security Configuration

This example illustrates the hardened defaults and new control blocks:

{
  "version": "0.6.0-alpha",
  "containment": "process",
  "process": { "commandLine": "node -e \"console.log('secure')\"" },
  "filesystem": { "readwritePaths": ["/tmp"] },
  "network": {
    "defaultPolicy": "block",
    "allowedHosts": ["api.example.com"]
  },
  "ui": { "disable": true, "clipboard": "none" },
  "fallback": { "allowDaclMutation": false }
}

The network default is now "block", and the fallback object explicitly prevents host ACL modification.

0.7.0-dev Experimental Backend

This configuration leverages the WSL-Container experimental backend:

{
  "version": "0.7.0-dev",
  "containment": "wslc",
  "process": { "commandLine": "/bin/sh -c 'echo experimental'" },
  "experimental": {
    "wslc": {
      "cpuCount": 2,
      "memoryMb": 1024,
      "gpu": true
    }
  },
  "network": {
    "defaultPolicy": "block",
    "allowedHosts": ["dev.local"]
  }
}

The experimental.wslc block provides backend-specific tuning parameters unavailable in stable releases.

Implementation Files

The schema evolution is enforced by specific runtime components:

• schemas/stable/mxc-config.schema.0.5.0-alpha.json: Defines process abstraction and processContainer introduction
• schemas/stable/mxc-config.schema.0.6.0-alpha.json: Implements fallback controls and network security defaults
• schemas/dev/mxc-config.schema.0.7.0-dev.json: Provides experimental namespace validation
• sdk/src/sandbox.ts: Runtime helper that inspects the version field and selects appropriate backend implementations
• sdk/src/platform.ts: Contains platform-specific logic that resolves abstract process containment to concrete OS-specific backends

Summary

• 0.5.0-alpha introduces abstract process containment and the processContainer block, establishing the foundation for cross-platform configuration
• 0.6.0-alpha hardens security with network.defaultPolicy set to "block", adds explicit fallback controls for host mutations, and separates UI policies into a top-level block
• 0.7.0-dev expands backend support through the experimental namespace, enabling configuration of bleeding-edge containment mechanisms like wslc and windows_sandbox without breaking stable schema contracts
• Runtime resolution of these schemas occurs in sdk/src/sandbox.ts and sdk/src/platform.ts, which validate the version field and instantiate appropriate backend drivers

Frequently Asked Questions

How do I migrate from 0.5.0-alpha to 0.6.0-alpha?

Update your schema identifier to reference schemas/stable/mxc-config.schema.0.6.0-alpha.json, change network.defaultPolicy from "allow" to "block" while adding explicit allowedHosts, and introduce a fallback object to control host mutation behaviors. If you previously relied on implicit ACL modifications, set fallback.allowDaclMutation to true temporarily, then refactor to remove the dependency.

What is the difference between process and processContainer containment?

In the MXC schema, process is an abstract containment intent specified in the containment field that the SDK resolves at runtime to appropriate backends via sdk/src/platform.ts. The processContainer block is a concrete configuration section containing Windows-specific settings like capabilities and UI policies, replacing the legacy appContainer structure while maintaining compatibility aliases.

Can I use experimental backends like wslc in production environments?

Experimental backends defined in schemas/dev/mxc-config.schema.0.7.0-dev.json are not recommended for production workloads. The experimental namespace explicitly isolates unstable features that may change without backward compatibility guarantees. For production use, select stable backends (processcontainer, bubblewrap, lxc) using the 0.6.0-alpha schema.

Why did the default network policy change to block in 0.6.0-alpha?

The change from "allow" to "block" aligns with zero-trust security principles and defense-in-depth strategies. This breaking change prevents accidental data exfiltration by requiring explicit host whitelisting through allowedHosts arrays, ensuring developers consciously define network boundaries rather than inheriting permissive defaults.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}