[codex-analytics] add compaction analytics event (#17155)

- event for compaction analytics
- introduces thread-connection and thread metadata caches for data
denormalization, expected to be useful for denormalization onto core
emitted events in general
- threads analytics event client into core (mirrors approved
implementation in #16640)
- denormalizes key thread metadata: thread_source, subagent_source,
parent_thread_id, as well as app-server client and runtime metadata)
- compaction strategy defaults to memento, forward compatible with
expected prefill_compaction strategy

1. Manual standalone compact, local
`INFO | 2026-04-09 17:35:50 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d0-5cfb-70c0-bef9-165c3bf9b2df', 'turn_id':
'019d74d0-d7f6-7c81-acc6-aae2030243d6', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'manual', 'reason':
'user_requested', 'implementation': 'responses', 'phase':
'standalone_turn', 'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 20170, 'active_context_tokens_after':
4830, 'started_at': 1775781337, 'completed_at': 1775781350,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 13524} | `

2. Auto pre-turn compact, local
`INFO | 2026-04-09 17:37:30 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d2-45ef-71d1-9c93-23cc0c13d988', 'turn_id':
'019d74d2-7b42-7372-9f0e-c0da3f352328', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'auto', 'reason':
'context_limit', 'implementation': 'responses', 'phase': 'pre_turn',
'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 20063, 'active_context_tokens_after':
4822, 'started_at': 1775781444, 'completed_at': 1775781449,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 5497} | `

3. Auto mid-turn compact, local
`INFO | 2026-04-09 17:38:28 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d3-212f-7a20-8c0a-4816a978675e', 'turn_id':
'019d74d3-3ee1-7462-89f6-2ffbeefcd5e3', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'auto', 'reason':
'context_limit', 'implementation': 'responses', 'phase': 'mid_turn',
'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 20325, 'active_context_tokens_after':
14641, 'started_at': 1775781500, 'completed_at': 1775781508,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 7507} | `

4. Remote /responses/compact, manual standalone
`INFO | 2026-04-09 17:40:20 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d4-7a11-78a1-89f7-0535a1149416', 'turn_id':
'019d74d4-e087-7183-9c20-b1e40b7578c0', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'manual', 'reason':
'user_requested', 'implementation': 'responses_compact', 'phase':
'standalone_turn', 'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 23461, 'active_context_tokens_after':
6171, 'started_at': 1775781601, 'completed_at': 1775781620,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 18971} | `

codex-rs/analytics/src/analytics_client_tests.rs

@@ -3,6 +3,7 @@ use crate::events::AppServerRpcTransport;
 use crate::events::CodexAppMentionedEventRequest;
 use crate::events::CodexAppServerClientMetadata;
 use crate::events::CodexAppUsedEventRequest;
+use crate::events::CodexCompactionEventRequest;
 use crate::events::CodexPluginEventRequest;
 use crate::events::CodexPluginUsedEventRequest;
 use crate::events::CodexRuntimeMetadata;
@@ -18,6 +19,13 @@ use crate::facts::AnalyticsFact;
 use crate::facts::AppInvocation;
 use crate::facts::AppMentionedInput;
 use crate::facts::AppUsedInput;
+use crate::facts::CodexCompactionEvent;
+use crate::facts::CompactionImplementation;
+use crate::facts::CompactionPhase;
+use crate::facts::CompactionReason;
+use crate::facts::CompactionStatus;
+use crate::facts::CompactionStrategy;
+use crate::facts::CompactionTrigger;
 use crate::facts::CustomAnalyticsFact;
 use crate::facts::InvocationType;
 use crate::facts::PluginState;
@@ -59,6 +67,14 @@ use std::sync::Mutex;
 use tokio::sync::mpsc;
 
 fn sample_thread(thread_id: &str, ephemeral: bool) -> Thread {
+    sample_thread_with_source(thread_id, ephemeral, AppServerSessionSource::Exec)
+}
+
+fn sample_thread_with_source(
+    thread_id: &str,
+    ephemeral: bool,
+    source: AppServerSessionSource,
+) -> Thread {
     Thread {
         id: thread_id.to_string(),
         forked_from_id: None,
@@ -71,7 +87,7 @@ fn sample_thread(thread_id: &str, ephemeral: bool) -> Thread {
         path: None,
         cwd: PathBuf::from("/tmp"),
         cli_version: "0.0.0".to_string(),
-        source: AppServerSessionSource::Exec,
+        source,
         agent_nickname: None,
         agent_role: None,
         git_info: None,
@@ -97,11 +113,44 @@ fn sample_thread_start_response(thread_id: &str, ephemeral: bool, model: &str) -
     }
 }
 
+fn sample_app_server_client_metadata() -> CodexAppServerClientMetadata {
+    CodexAppServerClientMetadata {
+        product_client_id: DEFAULT_ORIGINATOR.to_string(),
+        client_name: Some("codex-tui".to_string()),
+        client_version: Some("1.0.0".to_string()),
+        rpc_transport: AppServerRpcTransport::Stdio,
+        experimental_api_enabled: Some(true),
+    }
+}
+
+fn sample_runtime_metadata() -> CodexRuntimeMetadata {
+    CodexRuntimeMetadata {
+        codex_rs_version: "0.1.0".to_string(),
+        runtime_os: "macos".to_string(),
+        runtime_os_version: "15.3.1".to_string(),
+        runtime_arch: "aarch64".to_string(),
+    }
+}
+
 fn sample_thread_resume_response(thread_id: &str, ephemeral: bool, model: &str) -> ClientResponse {
+    sample_thread_resume_response_with_source(
+        thread_id,
+        ephemeral,
+        model,
+        AppServerSessionSource::Exec,
+    )
+}
+
+fn sample_thread_resume_response_with_source(
+    thread_id: &str,
+    ephemeral: bool,
+    model: &str,
+    source: AppServerSessionSource,
+) -> ClientResponse {
     ClientResponse::ThreadResume {
         request_id: RequestId::Integer(2),
         response: ThreadResumeResponse {
-            thread: sample_thread(thread_id, ephemeral),
+            thread: sample_thread_with_source(thread_id, ephemeral, source),
             model: model.to_string(),
             model_provider: "openai".to_string(),
             service_tier: None,
@@ -254,6 +303,77 @@ fn app_used_event_serializes_expected_shape() {
     );
 }
 
+#[test]
+fn compaction_event_serializes_expected_shape() {
+    let event = TrackEventRequest::Compaction(Box::new(CodexCompactionEventRequest {
+        event_type: "codex_compaction_event",
+        event_params: crate::events::codex_compaction_event_params(
+            CodexCompactionEvent {
+                thread_id: "thread-1".to_string(),
+                turn_id: "turn-1".to_string(),
+                trigger: CompactionTrigger::Auto,
+                reason: CompactionReason::ContextLimit,
+                implementation: CompactionImplementation::ResponsesCompact,
+                phase: CompactionPhase::MidTurn,
+                strategy: CompactionStrategy::Memento,
+                status: CompactionStatus::Completed,
+                error: None,
+                active_context_tokens_before: 120_000,
+                active_context_tokens_after: 18_000,
+                started_at: 100,
+                completed_at: 106,
+                duration_ms: Some(6543),
+            },
+            sample_app_server_client_metadata(),
+            sample_runtime_metadata(),
+            Some("user"),
+            /*subagent_source*/ None,
+            /*parent_thread_id*/ None,
+        ),
+    }));
+
+    let payload = serde_json::to_value(&event).expect("serialize compaction event");
+
+    assert_eq!(
+        payload,
+        json!({
+            "event_type": "codex_compaction_event",
+            "event_params": {
+                "thread_id": "thread-1",
+                "turn_id": "turn-1",
+                "app_server_client": {
+                    "product_client_id": DEFAULT_ORIGINATOR,
+                    "client_name": "codex-tui",
+                    "client_version": "1.0.0",
+                    "rpc_transport": "stdio",
+                    "experimental_api_enabled": true
+                },
+                "runtime": {
+                    "codex_rs_version": "0.1.0",
+                    "runtime_os": "macos",
+                    "runtime_os_version": "15.3.1",
+                    "runtime_arch": "aarch64"
+                },
+                "thread_source": "user",
+                "subagent_source": null,
+                "parent_thread_id": null,
+                "trigger": "auto",
+                "reason": "context_limit",
+                "implementation": "responses_compact",
+                "phase": "mid_turn",
+                "strategy": "memento",
+                "status": "completed",
+                "error": null,
+                "active_context_tokens_before": 120000,
+                "active_context_tokens_after": 18000,
+                "started_at": 100,
+                "completed_at": 106,
+                "duration_ms": 6543
+            }
+        })
+    );
+}
+
 #[test]
 fn app_used_dedupe_is_keyed_by_turn_and_connector() {
     let (sender, _receiver) = mpsc::channel(1);
@@ -449,6 +569,120 @@ async fn initialize_caches_client_and_thread_lifecycle_publishes_once_initialize
     assert_eq!(payload[0]["event_params"]["parent_thread_id"], json!(null));
 }
 
+#[tokio::test]
+async fn compaction_event_ingests_custom_fact() {
+    let mut reducer = AnalyticsReducer::default();
+    let mut events = Vec::new();
+    let parent_thread_id =
+        codex_protocol::ThreadId::from_string("22222222-2222-2222-2222-222222222222")
+            .expect("valid parent thread id");
+
+    reducer
+        .ingest(
+            AnalyticsFact::Initialize {
+                connection_id: 7,
+                params: InitializeParams {
+                    client_info: ClientInfo {
+                        name: "codex-tui".to_string(),
+                        title: None,
+                        version: "1.0.0".to_string(),
+                    },
+                    capabilities: Some(InitializeCapabilities {
+                        experimental_api: false,
+                        opt_out_notification_methods: None,
+                    }),
+                },
+                product_client_id: DEFAULT_ORIGINATOR.to_string(),
+                runtime: sample_runtime_metadata(),
+                rpc_transport: AppServerRpcTransport::Websocket,
+            },
+            &mut events,
+        )
+        .await;
+    reducer
+        .ingest(
+            AnalyticsFact::Response {
+                connection_id: 7,
+                response: Box::new(sample_thread_resume_response_with_source(
+                    "thread-1",
+                    /*ephemeral*/ false,
+                    "gpt-5",
+                    AppServerSessionSource::SubAgent(SubAgentSource::ThreadSpawn {
+                        parent_thread_id,
+                        depth: 1,
+                        agent_path: None,
+                        agent_nickname: None,
+                        agent_role: None,
+                    }),
+                )),
+            },
+            &mut events,
+        )
+        .await;
+    events.clear();
+
+    reducer
+        .ingest(
+            AnalyticsFact::Custom(CustomAnalyticsFact::Compaction(Box::new(
+                CodexCompactionEvent {
+                    thread_id: "thread-1".to_string(),
+                    turn_id: "turn-compact".to_string(),
+                    trigger: CompactionTrigger::Manual,
+                    reason: CompactionReason::UserRequested,
+                    implementation: CompactionImplementation::Responses,
+                    phase: CompactionPhase::StandaloneTurn,
+                    strategy: CompactionStrategy::Memento,
+                    status: CompactionStatus::Failed,
+                    error: Some("context limit exceeded".to_string()),
+                    active_context_tokens_before: 131_000,
+                    active_context_tokens_after: 131_000,
+                    started_at: 100,
+                    completed_at: 101,
+                    duration_ms: Some(1200),
+                },
+            ))),
+            &mut events,
+        )
+        .await;
+
+    let payload = serde_json::to_value(&events).expect("serialize events");
+    assert_eq!(payload.as_array().expect("events array").len(), 1);
+    assert_eq!(payload[0]["event_type"], "codex_compaction_event");
+    assert_eq!(payload[0]["event_params"]["thread_id"], "thread-1");
+    assert_eq!(payload[0]["event_params"]["turn_id"], "turn-compact");
+    assert_eq!(
+        payload[0]["event_params"]["app_server_client"]["product_client_id"],
+        DEFAULT_ORIGINATOR
+    );
+    assert_eq!(
+        payload[0]["event_params"]["app_server_client"]["client_name"],
+        "codex-tui"
+    );
+    assert_eq!(
+        payload[0]["event_params"]["app_server_client"]["rpc_transport"],
+        "websocket"
+    );
+    assert_eq!(
+        payload[0]["event_params"]["runtime"]["codex_rs_version"],
+        "0.1.0"
+    );
+    assert_eq!(payload[0]["event_params"]["thread_source"], "subagent");
+    assert_eq!(
+        payload[0]["event_params"]["subagent_source"],
+        "thread_spawn"
+    );
+    assert_eq!(
+        payload[0]["event_params"]["parent_thread_id"],
+        "22222222-2222-2222-2222-222222222222"
+    );
+    assert_eq!(payload[0]["event_params"]["trigger"], "manual");
+    assert_eq!(payload[0]["event_params"]["reason"], "user_requested");
+    assert_eq!(payload[0]["event_params"]["implementation"], "responses");
+    assert_eq!(payload[0]["event_params"]["phase"], "standalone_turn");
+    assert_eq!(payload[0]["event_params"]["strategy"], "memento");
+    assert_eq!(payload[0]["event_params"]["status"], "failed");
+}
+
 #[test]
 fn subagent_thread_started_review_serializes_expected_shape() {
     let event = TrackEventRequest::ThreadInitialized(subagent_thread_started_event_request(

codex-rs/analytics/src/client.rs

@@ -178,6 +178,12 @@ impl AnalyticsEventsClient {
         )));
     }
 
+    pub fn track_compaction(&self, event: crate::facts::CodexCompactionEvent) {
+        self.record_fact(AnalyticsFact::Custom(CustomAnalyticsFact::Compaction(
+            Box::new(event),
+        )));
+    }
+
     pub fn track_plugin_installed(&self, plugin: PluginTelemetryMetadata) {
         self.record_fact(AnalyticsFact::Custom(
             CustomAnalyticsFact::PluginStateChanged(PluginStateChangedInput {

codex-rs/analytics/src/events.rs

@@ -1,4 +1,5 @@
 use crate::facts::AppInvocation;
+use crate::facts::CodexCompactionEvent;
 use crate::facts::InvocationType;
 use crate::facts::PluginState;
 use crate::facts::SubAgentThreadStartedInput;
@@ -37,6 +38,7 @@ pub(crate) enum TrackEventRequest {
     ThreadInitialized(ThreadInitializedEvent),
     AppMentioned(CodexAppMentionedEventRequest),
     AppUsed(CodexAppUsedEventRequest),
+    Compaction(Box<CodexCompactionEventRequest>),
     PluginUsed(CodexPluginUsedEventRequest),
     PluginInstalled(CodexPluginEventRequest),
     PluginUninstalled(CodexPluginEventRequest),
@@ -122,6 +124,35 @@ pub(crate) struct CodexAppUsedEventRequest {
     pub(crate) event_params: CodexAppMetadata,
 }
 
+#[derive(Serialize)]
+pub(crate) struct CodexCompactionEventParams {
+    pub(crate) thread_id: String,
+    pub(crate) turn_id: String,
+    pub(crate) app_server_client: CodexAppServerClientMetadata,
+    pub(crate) runtime: CodexRuntimeMetadata,
+    pub(crate) thread_source: Option<&'static str>,
+    pub(crate) subagent_source: Option<String>,
+    pub(crate) parent_thread_id: Option<String>,
+    pub(crate) trigger: crate::facts::CompactionTrigger,
+    pub(crate) reason: crate::facts::CompactionReason,
+    pub(crate) implementation: crate::facts::CompactionImplementation,
+    pub(crate) phase: crate::facts::CompactionPhase,
+    pub(crate) strategy: crate::facts::CompactionStrategy,
+    pub(crate) status: crate::facts::CompactionStatus,
+    pub(crate) error: Option<String>,
+    pub(crate) active_context_tokens_before: i64,
+    pub(crate) active_context_tokens_after: i64,
+    pub(crate) started_at: u64,
+    pub(crate) completed_at: u64,
+    pub(crate) duration_ms: Option<u64>,
+}
+
+#[derive(Serialize)]
+pub(crate) struct CodexCompactionEventRequest {
+    pub(crate) event_type: &'static str,
+    pub(crate) event_params: CodexCompactionEventParams,
+}
+
 #[derive(Serialize)]
 pub(crate) struct CodexPluginMetadata {
     pub(crate) plugin_id: Option<String>,
@@ -201,6 +232,37 @@ pub(crate) fn codex_plugin_metadata(plugin: PluginTelemetryMetadata) -> CodexPlu
     }
 }
 
+pub(crate) fn codex_compaction_event_params(
+    input: CodexCompactionEvent,
+    app_server_client: CodexAppServerClientMetadata,
+    runtime: CodexRuntimeMetadata,
+    thread_source: Option<&'static str>,
+    subagent_source: Option<String>,
+    parent_thread_id: Option<String>,
+) -> CodexCompactionEventParams {
+    CodexCompactionEventParams {
+        thread_id: input.thread_id,
+        turn_id: input.turn_id,
+        app_server_client,
+        runtime,
+        thread_source,
+        subagent_source,
+        parent_thread_id,
+        trigger: input.trigger,
+        reason: input.reason,
+        implementation: input.implementation,
+        phase: input.phase,
+        strategy: input.strategy,
+        status: input.status,
+        error: input.error,
+        active_context_tokens_before: input.active_context_tokens_before,
+        active_context_tokens_after: input.active_context_tokens_after,
+        started_at: input.started_at,
+        completed_at: input.completed_at,
+        duration_ms: input.duration_ms,
+    }
+}
+
 pub(crate) fn codex_plugin_used_metadata(
     tracking: &TrackEventsContext,
     plugin: PluginTelemetryMetadata,
@@ -260,7 +322,7 @@ pub(crate) fn subagent_thread_started_event_request(
     }
 }
 
-fn subagent_source_name(subagent_source: &SubAgentSource) -> String {
+pub(crate) fn subagent_source_name(subagent_source: &SubAgentSource) -> String {
     match subagent_source {
         SubAgentSource::Review => "review".to_string(),
         SubAgentSource::Compact => "compact".to_string(),
@@ -270,7 +332,7 @@ fn subagent_source_name(subagent_source: &SubAgentSource) -> String {
     }
 }
 
-fn subagent_parent_thread_id(subagent_source: &SubAgentSource) -> Option<String> {
+pub(crate) fn subagent_parent_thread_id(subagent_source: &SubAgentSource) -> Option<String> {
     match subagent_source {
         SubAgentSource::ThreadSpawn {
             parent_thread_id, ..

codex-rs/analytics/src/facts.rs

@@ -64,6 +64,69 @@ pub struct SubAgentThreadStartedInput {
     pub created_at: u64,
 }
 
+#[derive(Clone, Copy, Debug, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum CompactionTrigger {
+    Manual,
+    Auto,
+}
+
+#[derive(Clone, Copy, Debug, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum CompactionReason {
+    UserRequested,
+    ContextLimit,
+    ModelDownshift,
+}
+
+#[derive(Clone, Copy, Debug, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum CompactionImplementation {
+    Responses,
+    ResponsesCompact,
+}
+
+#[derive(Clone, Copy, Debug, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum CompactionPhase {
+    StandaloneTurn,
+    PreTurn,
+    MidTurn,
+}
+
+#[derive(Clone, Copy, Debug, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum CompactionStrategy {
+    Memento,
+    PrefixCompaction,
+}
+
+#[derive(Clone, Copy, Debug, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum CompactionStatus {
+    Completed,
+    Failed,
+    Interrupted,
+}
+
+#[derive(Clone)]
+pub struct CodexCompactionEvent {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub trigger: CompactionTrigger,
+    pub reason: CompactionReason,
+    pub implementation: CompactionImplementation,
+    pub phase: CompactionPhase,
+    pub strategy: CompactionStrategy,
+    pub status: CompactionStatus,
+    pub error: Option<String>,
+    pub active_context_tokens_before: i64,
+    pub active_context_tokens_after: i64,
+    pub started_at: u64,
+    pub completed_at: u64,
+    pub duration_ms: Option<u64>,
+}
+
 #[allow(dead_code)]
 pub(crate) enum AnalyticsFact {
     Initialize {
@@ -90,6 +153,7 @@ pub(crate) enum AnalyticsFact {
 
 pub(crate) enum CustomAnalyticsFact {
     SubAgentThreadStarted(SubAgentThreadStartedInput),
+    Compaction(Box<CodexCompactionEvent>),
     SkillInvoked(SkillInvokedInput),
     AppMentioned(AppMentionedInput),
     AppUsed(AppUsedInput),

codex-rs/analytics/src/lib.rs

@@ -6,6 +6,13 @@ mod reducer;
 pub use client::AnalyticsEventsClient;
 pub use events::AppServerRpcTransport;
 pub use facts::AppInvocation;
+pub use facts::CodexCompactionEvent;
+pub use facts::CompactionImplementation;
+pub use facts::CompactionPhase;
+pub use facts::CompactionReason;
+pub use facts::CompactionStatus;
+pub use facts::CompactionStrategy;
+pub use facts::CompactionTrigger;
 pub use facts::InvocationType;
 pub use facts::SkillInvocation;
 pub use facts::SubAgentThreadStartedInput;

codex-rs/analytics/src/reducer.rs

@@ -2,6 +2,7 @@ use crate::events::AppServerRpcTransport;
 use crate::events::CodexAppMentionedEventRequest;
 use crate::events::CodexAppServerClientMetadata;
 use crate::events::CodexAppUsedEventRequest;
+use crate::events::CodexCompactionEventRequest;
 use crate::events::CodexPluginEventRequest;
 use crate::events::CodexPluginUsedEventRequest;
 use crate::events::CodexRuntimeMetadata;
@@ -12,14 +13,18 @@ use crate::events::ThreadInitializedEvent;
 use crate::events::ThreadInitializedEventParams;
 use crate::events::TrackEventRequest;
 use crate::events::codex_app_metadata;
+use crate::events::codex_compaction_event_params;
 use crate::events::codex_plugin_metadata;
 use crate::events::codex_plugin_used_metadata;
 use crate::events::plugin_state_event_type;
+use crate::events::subagent_parent_thread_id;
+use crate::events::subagent_source_name;
 use crate::events::subagent_thread_started_event_request;
 use crate::events::thread_source_name;
 use crate::facts::AnalyticsFact;
 use crate::facts::AppMentionedInput;
 use crate::facts::AppUsedInput;
+use crate::facts::CodexCompactionEvent;
 use crate::facts::CustomAnalyticsFact;
 use crate::facts::PluginState;
 use crate::facts::PluginStateChangedInput;
@@ -40,6 +45,8 @@ use std::path::Path;
 #[derive(Default)]
 pub(crate) struct AnalyticsReducer {
     connections: HashMap<u64, ConnectionState>,
+    thread_connections: HashMap<String, u64>,
+    thread_metadata: HashMap<String, ThreadMetadataState>,
 }
 
 struct ConnectionState {
@@ -47,6 +54,35 @@ struct ConnectionState {
     runtime: CodexRuntimeMetadata,
 }
 
+#[derive(Clone)]
+struct ThreadMetadataState {
+    thread_source: Option<&'static str>,
+    subagent_source: Option<String>,
+    parent_thread_id: Option<String>,
+}
+
+impl ThreadMetadataState {
+    fn from_session_source(session_source: &SessionSource) -> Self {
+        let (subagent_source, parent_thread_id) = match session_source {
+            SessionSource::SubAgent(subagent_source) => (
+                Some(subagent_source_name(subagent_source)),
+                subagent_parent_thread_id(subagent_source),
+            ),
+            SessionSource::Cli
+            | SessionSource::VSCode
+            | SessionSource::Exec
+            | SessionSource::Mcp
+            | SessionSource::Custom(_)
+            | SessionSource::Unknown => (None, None),
+        };
+        Self {
+            thread_source: thread_source_name(session_source),
+            subagent_source,
+            parent_thread_id,
+        }
+    }
+}
+
 impl AnalyticsReducer {
     pub(crate) async fn ingest(&mut self, input: AnalyticsFact, out: &mut Vec<TrackEventRequest>) {
         match input {
@@ -81,6 +117,9 @@ impl AnalyticsReducer {
                 CustomAnalyticsFact::SubAgentThreadStarted(input) => {
                     self.ingest_subagent_thread_started(input, out);
                 }
+                CustomAnalyticsFact::Compaction(input) => {
+                    self.ingest_compaction(*input, out);
+                }
                 CustomAnalyticsFact::SkillInvoked(input) => {
                     self.ingest_skill_invoked(input, out).await;
                 }
@@ -254,27 +293,74 @@ impl AnalyticsReducer {
             _ => return,
         };
         let thread_source: SessionSource = thread.source.into();
+        let thread_id = thread.id;
         let Some(connection_state) = self.connections.get(&connection_id) else {
             return;
         };
+        let thread_metadata = ThreadMetadataState::from_session_source(&thread_source);
+        self.thread_connections
+            .insert(thread_id.clone(), connection_id);
+        self.thread_metadata
+            .insert(thread_id.clone(), thread_metadata.clone());
         out.push(TrackEventRequest::ThreadInitialized(
             ThreadInitializedEvent {
                 event_type: "codex_thread_initialized",
                 event_params: ThreadInitializedEventParams {
-                    thread_id: thread.id,
+                    thread_id,
                     app_server_client: connection_state.app_server_client.clone(),
                     runtime: connection_state.runtime.clone(),
                     model,
                     ephemeral: thread.ephemeral,
-                    thread_source: thread_source_name(&thread_source),
+                    thread_source: thread_metadata.thread_source,
                     initialization_mode,
-                    subagent_source: None,
-                    parent_thread_id: None,
+                    subagent_source: thread_metadata.subagent_source,
+                    parent_thread_id: thread_metadata.parent_thread_id,
                     created_at: u64::try_from(thread.created_at).unwrap_or_default(),
                 },
             },
         ));
     }
+
+    fn ingest_compaction(&mut self, input: CodexCompactionEvent, out: &mut Vec<TrackEventRequest>) {
+        let Some(connection_id) = self.thread_connections.get(&input.thread_id) else {
+            tracing::warn!(
+                thread_id = %input.thread_id,
+                turn_id = %input.turn_id,
+                "dropping compaction analytics event: missing thread connection metadata"
+            );
+            return;
+        };
+        let Some(connection_state) = self.connections.get(connection_id) else {
+            tracing::warn!(
+                thread_id = %input.thread_id,
+                turn_id = %input.turn_id,
+                connection_id,
+                "dropping compaction analytics event: missing connection metadata"
+            );
+            return;
+        };
+        let Some(thread_metadata) = self.thread_metadata.get(&input.thread_id) else {
+            tracing::warn!(
+                thread_id = %input.thread_id,
+                turn_id = %input.turn_id,
+                "dropping compaction analytics event: missing thread lifecycle metadata"
+            );
+            return;
+        };
+        out.push(TrackEventRequest::Compaction(Box::new(
+            CodexCompactionEventRequest {
+                event_type: "codex_compaction_event",
+                event_params: codex_compaction_event_params(
+                    input,
+                    connection_state.app_server_client.clone(),
+                    connection_state.runtime.clone(),
+                    thread_metadata.thread_source,
+                    thread_metadata.subagent_source.clone(),
+                    thread_metadata.parent_thread_id.clone(),
+                ),
+            },
+        )));
+    }
 }
 
 pub(crate) fn skill_id_for_local_skill(