diff --git a/src/services/sqlite/PendingMessageStore.ts b/src/services/sqlite/PendingMessageStore.ts
index bb2d33ef..b61a9ea8 100644
--- a/src/services/sqlite/PendingMessageStore.ts
+++ b/src/services/sqlite/PendingMessageStore.ts
@@ -397,6 +397,19 @@ export class PendingMessageStore {
     return result.count;
   }
 
+  /**
+   * Peek at pending message types for a session (for tier routing).
+   * Returns list of { message_type, tool_name } without claiming.
+   */
+  peekPendingTypes(sessionDbId: number): Array<{ message_type: string; tool_name: string | null }> {
+    const stmt = this.db.prepare(`
+      SELECT message_type, tool_name FROM pending_messages
+      WHERE session_db_id = ? AND status IN ('pending', 'processing')
+      ORDER BY id ASC
+    `);
+    return stmt.all(sessionDbId) as Array<{ message_type: string; tool_name: string | null }>;
+  }
+
   /**
    * Check if any session has pending work.
    * Excludes 'processing' messages stuck for >5 minutes (resets them to 'pending' as a side effect).
diff --git a/src/services/sqlite/migrations.ts b/src/services/sqlite/migrations.ts
index ad0f877b..5be21f6a 100644
--- a/src/services/sqlite/migrations.ts
+++ b/src/services/sqlite/migrations.ts
@@ -509,6 +509,38 @@ export const migration007: Migration = {
 };
 
 
+/**
+ * All migrations in order
+ */
+/**
+ * Migration 008: Observation feedback table for tracking observation usage
+ *
+ * Tracks how observations are used (semantic injection hits, search access,
+ * explicit retrieval). Foundation for future Thompson Sampling optimization.
+ */
+export const migration008: Migration = {
+  version: 25,
+  up: (db: Database) => {
+    db.run(`
+      CREATE TABLE IF NOT EXISTS observation_feedback (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        observation_id INTEGER NOT NULL,
+        signal_type TEXT NOT NULL,
+        session_db_id INTEGER,
+        created_at_epoch INTEGER NOT NULL,
+        metadata TEXT,
+        FOREIGN KEY (observation_id) REFERENCES observations(id) ON DELETE CASCADE
+      )
+    `);
+    db.run(`CREATE INDEX IF NOT EXISTS idx_feedback_observation ON observation_feedback(observation_id)`);
+    db.run(`CREATE INDEX IF NOT EXISTS idx_feedback_signal ON observation_feedback(signal_type)`);
+    console.log('✅ Created observation_feedback table for usage tracking');
+  },
+  down: (db: Database) => {
+    db.run(`DROP TABLE IF EXISTS observation_feedback`);
+  }
+};
+
 /**
  * All migrations in order
  */
@@ -519,5 +551,6 @@ export const migrations: Migration[] = [
   migration004,
   migration005,
   migration006,
-  migration007
+  migration007,
+  migration008
 ];
\ No newline at end of file
diff --git a/src/services/sqlite/migrations/runner.ts b/src/services/sqlite/migrations/runner.ts
index 51c8a257..aff03d6e 100644
--- a/src/services/sqlite/migrations/runner.ts
+++ b/src/services/sqlite/migrations/runner.ts
@@ -34,6 +34,7 @@ export class MigrationRunner {
     this.addOnUpdateCascadeToForeignKeys();
     this.addObservationContentHashColumn();
     this.addSessionCustomTitleColumn();
+    this.createObservationFeedbackTable();
   }
 
   /**
@@ -863,4 +864,31 @@ export class MigrationRunner {
 
     this.db.prepare('INSERT OR IGNORE INTO schema_versions (version, applied_at) VALUES (?, ?)').run(23, new Date().toISOString());
   }
+
+  /**
+   * Create observation_feedback table for tracking observation usage signals.
+   * Foundation for tier routing optimization and future Thompson Sampling.
+   * Schema version 24.
+   */
+  private createObservationFeedbackTable(): void {
+    const applied = this.db.query('SELECT 1 FROM schema_versions WHERE version = 24').get();
+    if (applied) return;
+
+    this.db.run(`
+      CREATE TABLE IF NOT EXISTS observation_feedback (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        observation_id INTEGER NOT NULL,
+        signal_type TEXT NOT NULL,
+        session_db_id INTEGER,
+        created_at_epoch INTEGER NOT NULL,
+        metadata TEXT,
+        FOREIGN KEY (observation_id) REFERENCES observations(id) ON DELETE CASCADE
+      )
+    `);
+    this.db.run('CREATE INDEX IF NOT EXISTS idx_feedback_observation ON observation_feedback(observation_id)');
+    this.db.run('CREATE INDEX IF NOT EXISTS idx_feedback_signal ON observation_feedback(signal_type)');
+
+    this.db.prepare('INSERT OR IGNORE INTO schema_versions (version, applied_at) VALUES (?, ?)').run(24, new Date().toISOString());
+    logger.debug('DB', 'Created observation_feedback table for usage tracking');
+  }
 }
diff --git a/src/services/worker-types.ts b/src/services/worker-types.ts
index c4fd89eb..5962bfa4 100644
--- a/src/services/worker-types.ts
+++ b/src/services/worker-types.ts
@@ -40,6 +40,8 @@ export interface ActiveSession {
   // CLAIM-CONFIRM FIX: Track IDs of messages currently being processed
   // These IDs will be confirmed (deleted) after successful storage
   processingMessageIds: number[];
+  // Tier routing: model override per session based on queue complexity
+  modelOverride?: string;
 }
 
 export interface PendingMessage {
diff --git a/src/services/worker/SDKAgent.ts b/src/services/worker/SDKAgent.ts
index 2af48068..5a9b5866 100644
--- a/src/services/worker/SDKAgent.ts
+++ b/src/services/worker/SDKAgent.ts
@@ -49,8 +49,8 @@ export class SDKAgent {
     // Find Claude executable
     const claudePath = this.findClaudeExecutable();
 
-    // Get model ID and disallowed tools
-    const modelId = this.getModelId();
+    // Get model ID (tier routing override takes precedence)
+    const modelId = session.modelOverride || this.getModelId();
     // Memory agent is OBSERVER ONLY - no tools allowed
     const disallowedTools = [
       'Bash',           // Prevent infinite loops
diff --git a/src/services/worker/http/routes/SessionRoutes.ts b/src/services/worker/http/routes/SessionRoutes.ts
index 2f32efb5..9db84dc2 100644
--- a/src/services/worker/http/routes/SessionRoutes.ts
+++ b/src/services/worker/http/routes/SessionRoutes.ts
@@ -106,6 +106,8 @@ export class SessionRoutes extends BaseRouteHandler {
 
     // Start generator if not running
     if (!session.generatorPromise) {
+      // Apply tier routing before starting the generator
+      this.applyTierRouting(session);
       this.spawnInProgress.set(sessionDbId, true);
       this.startGeneratorWithProvider(session, selectedProvider, source);
       return;
@@ -126,6 +128,7 @@ export class SessionRoutes extends BaseRouteHandler {
       session.abortController = new AbortController();
       session.lastGeneratorActivity = Date.now();
       // Start a fresh generator
+      this.applyTierRouting(session);
       this.spawnInProgress.set(sessionDbId, true);
       this.startGeneratorWithProvider(session, selectedProvider, 'stale-recovery');
       return;
@@ -283,6 +286,7 @@ export class SessionRoutes extends BaseRouteHandler {
                 this.crashRecoveryScheduled.delete(sessionDbId);
                 const stillExists = this.sessionManager.getSession(sessionDbId);
                 if (stillExists && !stillExists.generatorPromise) {
+                  this.applyTierRouting(stillExists);
                   this.startGeneratorWithProvider(stillExists, this.getSelectedProvider(), 'crash-recovery');
                 }
               }, backoffMs);
@@ -813,4 +817,60 @@ export class SessionRoutes extends BaseRouteHandler {
       contextInjected
     });
   });
+
+  // Simple tool names that produce low-complexity observations
+  private static readonly SIMPLE_TOOLS = new Set([
+    'Read', 'Glob', 'Grep', 'LS', 'ListMcpResourcesTool'
+  ]);
+
+  /**
+   * Apply tier routing: select model based on pending queue complexity.
+   * - Summarize in queue → summary model (e.g., Opus)
+   * - All simple tools → simple model (e.g., Haiku)
+   * - Otherwise → default model (no override)
+   */
+  private applyTierRouting(session: NonNullable<ReturnType<typeof this.sessionManager.getSession>>): void {
+    const settings = SettingsDefaultsManager.loadFromFile(USER_SETTINGS_PATH);
+    if (settings.CLAUDE_MEM_TIER_ROUTING_ENABLED === 'false') {
+      session.modelOverride = undefined;
+      return;
+    }
+
+    // Clear stale override before re-evaluating — prevents previous tier
+    // from persisting when queue composition changes between spawns.
+    session.modelOverride = undefined;
+
+    const pendingStore = this.sessionManager.getPendingMessageStore();
+    const pending = pendingStore.peekPendingTypes(session.sessionDbId);
+
+    if (pending.length === 0) {
+      session.modelOverride = undefined;
+      return;
+    }
+
+    const hasSummarize = pending.some(m => m.message_type === 'summarize');
+    const allSimple = pending.every(m =>
+      m.message_type === 'observation' && m.tool_name && SessionRoutes.SIMPLE_TOOLS.has(m.tool_name)
+    );
+
+    if (hasSummarize) {
+      const summaryModel = settings.CLAUDE_MEM_TIER_SUMMARY_MODEL;
+      if (summaryModel) {
+        session.modelOverride = summaryModel;
+        logger.debug('SESSION', `Tier routing: summary model`, {
+          sessionId: session.sessionDbId, model: summaryModel
+        });
+      }
+    } else if (allSimple) {
+      const simpleModel = settings.CLAUDE_MEM_TIER_SIMPLE_MODEL;
+      if (simpleModel) {
+        session.modelOverride = simpleModel;
+        logger.debug('SESSION', `Tier routing: simple model`, {
+          sessionId: session.sessionDbId, model: simpleModel
+        });
+      }
+    } else {
+      session.modelOverride = undefined;
+    }
+  }
 }
diff --git a/src/shared/SettingsDefaultsManager.ts b/src/shared/SettingsDefaultsManager.ts
index faa4d2ad..6d347f5a 100644
--- a/src/shared/SettingsDefaultsManager.ts
+++ b/src/shared/SettingsDefaultsManager.ts
@@ -57,6 +57,10 @@ export interface SettingsDefaults {
   // Semantic Context Injection (per-prompt via Chroma)
   CLAUDE_MEM_SEMANTIC_INJECT: string;        // 'true' | 'false' - inject relevant observations on each prompt
   CLAUDE_MEM_SEMANTIC_INJECT_LIMIT: string;  // Max observations to inject per prompt
+  // Tier Routing (model selection by queue complexity)
+  CLAUDE_MEM_TIER_ROUTING_ENABLED: string;   // 'true' | 'false' - enable model tier routing
+  CLAUDE_MEM_TIER_SIMPLE_MODEL: string;      // Tier alias or model ID for simple tool observations (Read, Glob, Grep)
+  CLAUDE_MEM_TIER_SUMMARY_MODEL: string;     // Tier alias or model ID for session summaries
   // Chroma Vector Database Configuration
   CLAUDE_MEM_CHROMA_ENABLED: string;   // 'true' | 'false' - set to 'false' for SQLite-only mode
   CLAUDE_MEM_CHROMA_MODE: string;      // 'local' | 'remote'
@@ -119,6 +123,10 @@ export class SettingsDefaultsManager {
     // Semantic Context Injection (per-prompt via Chroma vector search)
     CLAUDE_MEM_SEMANTIC_INJECT: 'true',              // Inject relevant past observations on every UserPromptSubmit
     CLAUDE_MEM_SEMANTIC_INJECT_LIMIT: '5',           // Top-N most relevant observations to inject per prompt
+    // Tier Routing (model selection by queue complexity)
+    CLAUDE_MEM_TIER_ROUTING_ENABLED: 'true',         // Route observations to models by complexity
+    CLAUDE_MEM_TIER_SIMPLE_MODEL: 'haiku', // Portable tier alias — works across Direct API, Bedrock, Vertex, Azure (see #1463)
+    CLAUDE_MEM_TIER_SUMMARY_MODEL: '',                // Empty = use default model for summaries
     // Chroma Vector Database Configuration
     CLAUDE_MEM_CHROMA_ENABLED: 'true',         // Set to 'false' to disable Chroma and use SQLite-only search
     CLAUDE_MEM_CHROMA_MODE: 'local',           // 'local' uses persistent chroma-mcp via uvx, 'remote' connects to existing server