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Deprecations

This page lists active deprecations and migration guidance.

Deprecated as of 2026-06-11; sunsets on 2026-07-07

The Rust MCP runtime sidecar, Rust A2A runtime sidecar, and ValidationMiddleware are deprecated. They remain available for existing deployments, but new deployments should use the default Python runtime paths and endpoint-level validation. They are scheduled for sunset on 2026-07-07.

Rust MCP runtime sidecar

Deprecated controls include RUST_MCP_MODE, EXPERIMENTAL_RUST_MCP_*, and MCP_RUST_* settings that enable or configure the Rust MCP sidecar.

Use the default Python MCP transport path by leaving RUST_MCP_MODE=off and EXPERIMENTAL_RUST_MCP_RUNTIME_ENABLED=false.

Runtime signals:

  • Gateway startup logs include a deprecation warning when the Rust MCP runtime path is enabled.
  • Rust MCP runtime responses include Deprecation, Sunset, and Link: <...>; rel="deprecation" headers.

ValidationMiddleware

mcpgateway.middleware.validation_middleware.ValidationMiddleware is deprecated.

Use endpoint-level Pydantic models, the existing SecurityValidator helpers, and protocol-specific validation middleware instead. Leave VALIDATION_MIDDLEWARE_ENABLED=false unless you need compatibility with an existing deployment that already depends on this middleware.

Runtime signals:

  • Gateway startup logs include a deprecation warning when the middleware is enabled.
  • Instantiating the middleware emits a Python DeprecationWarning.

Legacy MCP HTTP+SSE transport

The MCP specification deprecated the legacy two-endpoint HTTP+SSE transport in protocol version 2025-03-26 in favor of Streamable HTTP. This is distinct from SSE response streams within Streamable HTTP and from the 2026-07-07 ContextForge component sunset above. ContextForge has not assigned a removal date to its SSE gateway compatibility path, which remains available through the control plane.

Use Streamable HTTP for new gateway registrations. The experimental dataplane publisher (DATAPLANE_PUBLISHER) publishes only STREAMABLEHTTP gateway backends. If filtering leaves a virtual server with no publishable backends, the publisher omits that virtual host so a split deployment can use the dataplane's 404 response to fall back to the control plane.

See the MCP deprecated-feature registry and transport guidance.