diff --git a/projects/packages/jetpack-mu-wpcom/changelog/add-pcg-log-blocked-activation b/projects/packages/jetpack-mu-wpcom/changelog/add-pcg-log-blocked-activation
new file mode 100644
index 000000000000..6c01b367f3f7
--- /dev/null
+++ b/projects/packages/jetpack-mu-wpcom/changelog/add-pcg-log-blocked-activation
@@ -0,0 +1,4 @@
+Significance: patch
+Type: added
+
+Plugin Conflicts Guardian: emit logstash events when the guard refuses or recovers from a bad change — `Activation blocked` (refused activation), `Update blocked` (refused install/update with a parse error), and `Update rolled back` (post-update fatal triggered a rollback). All three share the `plugin-conflicts-guardian` feature bucket so the full PCG-block surface can be measured from one filter.
diff --git a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/activation-guard.php b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/activation-guard.php
index 441ca8f3a6fb..b5ee1bcab46f 100644
--- a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/activation-guard.php
+++ b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/activation-guard.php
@@ -114,21 +114,48 @@ function pcg_guard_evaluate_plugins( $plugins ) {
 
 	$blocked_plugin = pcg_guard_get_blocked_plugin( $result, $paths );
 	if ( '' !== $blocked_plugin ) {
-		return array(
+		$blocked = array(
 			$blocked_plugin => pcg_guard_format_block_reason( $result ),
 		);
+	} else {
+		// Verdict didn't pin a specific plugin (e.g. probe terminated without a
+		// JSON body, or the captured `file` was outside any candidate's tree).
+		// Surface a batch-level message so we don't blame an arbitrary plugin.
+		$reason = sprintf(
+			/* translators: 1: locale-formatted list of plugin basenames; 2: probe verdict reason. */
+			__( 'One of these plugins caused a fatal during the pre-flight check: %1$s. Reason: %2$s', 'jetpack-mu-wpcom' ),
+			wp_sprintf_l( '%l', array_keys( $paths ) ),
+			pcg_guard_format_block_reason( $result )
+		);
+		$blocked = array( '' => $reason );
 	}
 
-	// Verdict didn't pin a specific plugin (e.g. probe terminated without a
-	// JSON body, or the captured `file` was outside any candidate's tree).
-	// Surface a batch-level message so we don't blame an arbitrary plugin.
-	$reason = sprintf(
-		/* translators: 1: locale-formatted list of plugin basenames; 2: probe verdict reason. */
-		__( 'One of these plugins caused a fatal during the pre-flight check: %1$s. Reason: %2$s', 'jetpack-mu-wpcom' ),
-		wp_sprintf_l( '%l', array_keys( $paths ) ),
-		pcg_guard_format_block_reason( $result )
+	pcg_guard_log_blocked_activation( array_keys( $paths ), $blocked, $result );
+
+	return $blocked;
+}
+
+/**
+ * Log an activation block to logstash. Best-effort; no-op off WordPress.com.
+ *
+ * @param string[]             $checked Probe batch as basenames.
+ * @param array<string,string> $blocked Map of basename => admin-notice reason. Empty-string key = batch-level fallback.
+ * @param array                $result  Probe verdict from PCG_Load_Tester::test().
+ * @return void
+ */
+function pcg_guard_log_blocked_activation( array $checked, array $blocked, array $result ) {
+	pcg_log_event(
+		'Activation blocked',
+		array(
+			'checked' => $checked,
+			'blocked' => array_keys( $blocked ),
+			'status'  => (string) ( $result['status'] ?? '' ),
+			// Basename only — absolute paths leak install layout.
+			'file'    => isset( $result['file'] ) ? basename( (string) $result['file'] ) : '',
+			'line'    => (int) ( $result['line'] ?? 0 ),
+			'reason'  => (string) ( $result['message'] ?? '' ),
+		)
 	);
-	return array( '' => $reason );
 }
 
 /**
diff --git a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/class-pcg-load-tester.php b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/class-pcg-load-tester.php
index e4c3e8402ef1..128f6de1f6d3 100644
--- a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/class-pcg-load-tester.php
+++ b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/class-pcg-load-tester.php
@@ -133,27 +133,13 @@ protected function is_error( $result ) {
 	 * @return void
 	 */
 	protected function log_probe_error( $mode, array $plugin_mains, array $front_result, array $admin_result ) {
-		if ( ! function_exists( 'log2logstash' ) ) {
-			$log2logstash_path = WP_CONTENT_DIR . '/lib/log2logstash/log2logstash.php';
-			if ( ! is_readable( $log2logstash_path ) ) {
-				return;
-			}
-			require_once $log2logstash_path;
-		}
-
-		log2logstash(
+		pcg_log_event(
+			'Probe transport error',
 			array(
-				'feature' => 'plugin-conflicts-guardian',
-				'message' => 'Probe transport error',
-				'extra'   => wp_json_encode(
-					array(
-						'mode'    => $mode,
-						'plugins' => $this->relative_basenames( $plugin_mains ),
-						'front'   => $this->probe_error_reason( $front_result ),
-						'admin'   => $this->probe_error_reason( $admin_result ),
-					),
-					JSON_UNESCAPED_SLASHES
-				),
+				'mode'    => $mode,
+				'plugins' => $this->relative_basenames( $plugin_mains ),
+				'front'   => $this->probe_error_reason( $front_result ),
+				'admin'   => $this->probe_error_reason( $admin_result ),
 			)
 		);
 	}
diff --git a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/pcg-log.php b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/pcg-log.php
new file mode 100644
index 000000000000..be2bcd3be7a8
--- /dev/null
+++ b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/pcg-log.php
@@ -0,0 +1,69 @@
+<?php
+/**
+ * Shared logstash dispatch for the Plugin Conflicts Guardian feature.
+ *
+ * @package automattic/jetpack-mu-wpcom
+ */
+
+/**
+ * Emit an event to the `plugin-conflicts-guardian` logstash bucket.
+ *
+ * Best-effort: a logging failure must never escalate into a fatal,
+ * since callers run on activation / install / update request paths.
+ * No-op outside WordPress.com (no `log2logstash` available).
+ *
+ * @param string $message Event message slug (e.g. "Activation blocked").
+ * @param array  $extra   Event-specific properties; JSON-encoded into the `extra` field.
+ * @return void
+ */
+function pcg_log_event( $message, array $extra ) {
+	try {
+		if ( ! function_exists( 'log2logstash' ) ) {
+			$log2logstash_path = WP_CONTENT_DIR . '/lib/log2logstash/log2logstash.php';
+			if ( ! is_readable( $log2logstash_path ) ) {
+				return;
+			}
+			require_once $log2logstash_path;
+		}
+
+		log2logstash(
+			array(
+				'feature' => 'plugin-conflicts-guardian',
+				'message' => (string) $message,
+				'extra'   => wp_json_encode( pcg_log_redact_paths( $extra ), JSON_UNESCAPED_SLASHES ),
+			)
+		);
+	} catch ( \Throwable $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch -- best-effort: a logging failure must not escalate on activation / install / update request paths.
+		unset( $e );
+	}
+}
+
+/**
+ * Recursively replace `ABSPATH` and `WP_CONTENT_DIR` prefixes inside string
+ * values with `.../` so log lines don't leak the install layout. Keeps the
+ * relative tail (`plugins/foo/bar.php`), which is the useful part for triage.
+ *
+ * @param mixed $value Scalar or array.
+ * @return mixed
+ */
+function pcg_log_redact_paths( $value ) {
+	if ( is_array( $value ) ) {
+		return array_map( 'pcg_log_redact_paths', $value );
+	}
+	if ( ! is_string( $value ) || '' === $value ) {
+		return $value;
+	}
+	// WP_CONTENT_DIR first — it's a longer prefix that's typically *under*
+	// ABSPATH on standard installs, so swapping ABSPATH first would shadow it.
+	$replacements = array();
+	if ( defined( 'WP_CONTENT_DIR' ) && '' !== WP_CONTENT_DIR ) {
+		$replacements[ rtrim( WP_CONTENT_DIR, '/' ) . '/' ] = '.../';
+	}
+	if ( defined( 'ABSPATH' ) && '' !== ABSPATH ) {
+		$replacements[ rtrim( ABSPATH, '/' ) . '/' ] = '.../';
+	}
+	if ( empty( $replacements ) ) {
+		return $value;
+	}
+	return strtr( $value, $replacements );
+}
diff --git a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/plugin-conflicts-guardian.php b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/plugin-conflicts-guardian.php
index 78e87f85afb1..60efc8ef296d 100644
--- a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/plugin-conflicts-guardian.php
+++ b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/plugin-conflicts-guardian.php
@@ -10,6 +10,7 @@
 /**
  * Load dependencies.
  */
+require_once __DIR__ . '/pcg-log.php';
 require_once __DIR__ . '/class-pcg-load-tester.php';
 
 // Probe endpoint must answer front-end requests, so it's not gated on is_admin().
diff --git a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-guard.php b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-guard.php
index c1f8ca1c9369..73f73f76304a 100644
--- a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-guard.php
+++ b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-guard.php
@@ -56,6 +56,9 @@ function pcg_update_guard_check( $source, $remote_source, $upgrader, $hook_extra
 	}
 
 	$first = $scan['errors'][0];
+
+	pcg_update_guard_log_blocked( $action, $hook_extra, $scan, (string) $source );
+
 	return new WP_Error(
 		'pcg_update_parse_error',
 		sprintf(
@@ -70,6 +73,38 @@ function pcg_update_guard_check( $source, $remote_source, $upgrader, $hook_extra
 	);
 }
 
+/**
+ * Log a refused install/update to logstash. Best-effort; no-op off WordPress.com.
+ *
+ * @param string $action     `install` or `update`.
+ * @param array  $hook_extra Hook payload from `upgrader_source_selection`.
+ * @param array  $scan       Result from `pcg_update_guard_scan_for_parse_errors()`.
+ * @param string $source     Extracted package directory (fallback slug source on installs,
+ *                           since `Plugin_Upgrader::install()` doesn't populate `hook_extra['plugin']`).
+ * @return void
+ */
+function pcg_update_guard_log_blocked( $action, array $hook_extra, array $scan, $source = '' ) {
+	$first = $scan['errors'][0];
+
+	$slug = (string) ( $hook_extra['plugin'] ?? ( $hook_extra['theme'] ?? '' ) );
+	if ( '' === $slug && '' !== $source ) {
+		$slug = basename( untrailingslashit( $source ) );
+	}
+
+	pcg_log_event(
+		'Update blocked',
+		array(
+			'action'      => (string) $action,
+			'slug'        => $slug,
+			// Basename only — absolute paths leak install layout.
+			'file'        => basename( (string) $first['file'] ),
+			'line'        => (int) $first['line'],
+			'reason'      => (string) $first['message'],
+			'error_count' => count( $scan['errors'] ),
+		)
+	);
+}
+
 /**
  * Tokenize every `.php` under $dir with TOKEN_PARSE and collect the failures.
  * Bails out once the wall-clock budget is exceeded.
diff --git a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-healthcheck.php b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-healthcheck.php
index 2705d9b13009..3c8f1e405c59 100644
--- a/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-healthcheck.php
+++ b/projects/packages/jetpack-mu-wpcom/src/features/plugin-conflicts-guardian/update-healthcheck.php
@@ -140,6 +140,7 @@ function pcg_healthcheck_after_update( $upgrader, $hook_extra ) { // phpcs:ignor
 	foreach ( $candidates as $candidate ) {
 		$rollback = PCG_Rollback::to_snapshot( $candidate['snapshot'] );
 		pcg_healthcheck_stash_notice( $candidate['plugin_file'], $result, $rollback, $candidate['plugin_name'], $candidate['new_version'] );
+		pcg_healthcheck_log_rollback( $candidate, $result, $rollback );
 
 		/**
 		 * Fires after a post-update probe fails and rollback has been attempted.
@@ -153,6 +154,32 @@ function pcg_healthcheck_after_update( $upgrader, $hook_extra ) { // phpcs:ignor
 	}
 }
 
+/**
+ * Log a post-update rollback to logstash. Best-effort; no-op off WordPress.com.
+ *
+ * @param array $candidate Per-plugin context built in `pcg_healthcheck_after_update()`.
+ * @param array $probe     Shared probe verdict from `PCG_Load_Tester::test()`.
+ * @param array $rollback  Result from `PCG_Rollback::to_snapshot()`.
+ * @return void
+ */
+function pcg_healthcheck_log_rollback( array $candidate, array $probe, array $rollback ) {
+	pcg_log_event(
+		'Update rolled back',
+		array(
+			'plugin'           => (string) $candidate['plugin_file'],
+			'new_version'      => (string) $candidate['new_version'],
+			'previous_version' => (string) ( $candidate['snapshot']['version'] ?? '' ),
+			'probe_status'     => (string) ( $probe['status'] ?? '' ),
+			// Basename only — absolute paths leak install layout.
+			'probe_file'       => isset( $probe['file'] ) ? basename( (string) $probe['file'] ) : '',
+			'probe_line'       => (int) ( $probe['line'] ?? 0 ),
+			'probe_reason'     => (string) ( $probe['message'] ?? '' ),
+			'rollback_status'  => (string) ( $rollback['status'] ?? '' ),
+			'restored_to'      => (string) ( $rollback['restored_to'] ?? '' ),
+		)
+	);
+}
+
 /**
  * Is this $hook_extra a plugin update (not an install, not a theme)?
  *
diff --git a/projects/packages/jetpack-mu-wpcom/tests/php/features/plugin-conflicts-guardian/Plugin_Conflicts_Guardian_Test.php b/projects/packages/jetpack-mu-wpcom/tests/php/features/plugin-conflicts-guardian/Plugin_Conflicts_Guardian_Test.php
index 4f4a8f8afb1a..d1cef85e4864 100644
--- a/projects/packages/jetpack-mu-wpcom/tests/php/features/plugin-conflicts-guardian/Plugin_Conflicts_Guardian_Test.php
+++ b/projects/packages/jetpack-mu-wpcom/tests/php/features/plugin-conflicts-guardian/Plugin_Conflicts_Guardian_Test.php
@@ -8,6 +8,7 @@
 use Automattic\Jetpack\Jetpack_Mu_Wpcom;
 use PHPUnit\Framework\Attributes\DataProvider;
 
+require_once Jetpack_Mu_Wpcom::PKG_DIR . 'src/features/plugin-conflicts-guardian/pcg-log.php';
 require_once Jetpack_Mu_Wpcom::PKG_DIR . 'src/features/plugin-conflicts-guardian/class-pcg-load-tester.php';
 require_once Jetpack_Mu_Wpcom::PKG_DIR . 'src/features/plugin-conflicts-guardian/activation-guard.php';
 require_once Jetpack_Mu_Wpcom::PKG_DIR . 'src/features/plugin-conflicts-guardian/update-guard.php';