1. URL-Path Major Versioning & Additive Compatibility

Major breaking API revisions are isolated by URL path prefix (/api/v1/*) and echoed on every response via X-API-Version and API-Version headers. Within an active major version, Systemores only ships backward-compatible changes such as new optional query parameters, new MCP diagnostic tools, or additive response fields.

2. 180-Day Minimum Sunset Window & RFC Headers

Before retiring any documented endpoint, MCP tool name, or schema contract, Systemores provides at least 180 calendar days of advance notice via:

RFC 9745 Deprecation Header: Timestamp marker (Deprecation: @<unix-timestamp>) emitted on affected responses.
RFC 8594 Sunset Header: Exact HTTP-date when traffic cutover occurs.
RFC 8288 Link Header: Pointer to migration instructions with rel="deprecation" and rel="successor-version".

3. Active Versions & Deprecation Schedule

All /api/v1/* routes, /api/audit, /api/health, /api/incidents, /api/stats, and /api/mcp (alias /mcp) endpoints are currently Active with zero scheduled deprecations or pending sunsets.