diff --git a/CHANGELOG.md b/CHANGELOG.md
index f13dd3a..32cc8d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,8 +6,26 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+## [v0.4.0] - 2026-07-16
+
 ### Added
 
+* **Mode control (first mutating RPC).** New `SetMode` RPC on `EconetService`,
+  exposed over gRPC, the REST gateway (`POST /v1alpha1/devices/{serial}/mode`),
+  and as an MCP tool. Writes go out over ClearBlade's REST publish endpoint
+  (`POST /message/{systemKey}/publish`, topic `user/{account_id}/device/desired`,
+  payload `{"@MODE": <idx>, ...}`) — the HTTP equivalent of the app's MQTT
+  publish, so **no MQTT client is required**. The mode is applied
+  asynchronously by the Rheem cloud and only reflected on a later poll.
+* `Mode` proto enum (`off`, `electric`, `energy-saving`, `heat-pump`,
+  `high-demand`, `gas`, `performance`, `vacation`) with protovalidate rejecting
+  the unspecified value. The enum flows into the MCP tool's input schema, so
+  clients see the valid modes. Supported modes are validated per-device against
+  the unit's reported mode list (`@MODE` is published as an index into it).
+* Generated MCP server (`econetmcpgen`) built from the proto via
+  `protoc-gen-go-mcp`, now mounted at `/api/mcp`, forwarding in-process to the
+  gRPC server through the go-sdk adapter. The hand-written `econetmcp` package
+  is retained as a one-line-switchable fallback in `pkg/econet/econet.go`.
 * Optional Grafana dashboard shipped as a ConfigMap in the Helm chart. Enable
   with `hull.config.settings.grafanaDashboard.enabled=true`; the ConfigMap is
   labeled `grafana_dashboard: "1"` for the Grafana sidecar to auto-import. The
@@ -17,6 +35,13 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   energy + cost + water usage, a heating-state timeline, WiFi signal, and a
   device-info table. Sidecar label/value and Grafana folder are configurable.
 
+### Changed
+
+* MCP tool surface changed with the switch to generated tools: `/api/mcp` now
+  serves `econet_v1alpha1_EconetService_ListDevices`, `_GetDevice`, and
+  `_SetMode` (structured JSON output) instead of the single `list_water_heaters`
+  summary tool. Switch back via the aliased import in `pkg/econet/econet.go`.
+
 ## [v0.3.0] - 2026-07-05
 
 ### Changed