diff --git a/codex-rs/core/src/client.rs b/codex-rs/core/src/client.rs
index 48e42ee0..52c034eb 100644
--- a/codex-rs/core/src/client.rs
+++ b/codex-rs/core/src/client.rs
@@ -398,9 +398,15 @@ impl From<ResponseCompletedUsage> for TokenUsage {
     fn from(val: ResponseCompletedUsage) -> Self {
         TokenUsage {
             input_tokens: val.input_tokens,
-            cached_input_tokens: val.input_tokens_details.map(|d| d.cached_tokens),
+            cached_input_tokens: val
+                .input_tokens_details
+                .map(|d| d.cached_tokens)
+                .unwrap_or(0),
             output_tokens: val.output_tokens,
-            reasoning_output_tokens: val.output_tokens_details.map(|d| d.reasoning_tokens),
+            reasoning_output_tokens: val
+                .output_tokens_details
+                .map(|d| d.reasoning_tokens)
+                .unwrap_or(0),
             total_tokens: val.total_tokens,
         }
     }
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 172d4e0f..95e9a969 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -99,6 +99,7 @@ use crate::protocol::SessionConfiguredEvent;
 use crate::protocol::StreamErrorEvent;
 use crate::protocol::Submission;
 use crate::protocol::TaskCompleteEvent;
+use crate::protocol::TokenUsageInfo;
 use crate::protocol::TurnDiffEvent;
 use crate::protocol::WebSearchBeginEvent;
 use crate::rollout::RolloutRecorder;
@@ -261,6 +262,7 @@ struct State {
     pending_approvals: HashMap<String, oneshot::Sender<ReviewDecision>>,
     pending_input: Vec<ResponseInputItem>,
     history: ConversationHistory,
+    token_info: Option<TokenUsageInfo>,
 }
 
 /// Context for an initialized model agent
@@ -1767,15 +1769,23 @@ async fn try_run_turn(
                 response_id: _,
                 token_usage,
             } => {
-                if let Some(token_usage) = token_usage {
-                    sess.tx_event
-                        .send(Event {
-                            id: sub_id.to_string(),
-                            msg: EventMsg::TokenCount(token_usage),
-                        })
-                        .await
-                        .ok();
-                }
+                let info = {
+                    let mut st = sess.state.lock_unchecked();
+                    let info = TokenUsageInfo::new_or_append(
+                        &st.token_info,
+                        &token_usage,
+                        turn_context.client.get_model_context_window(),
+                    );
+                    st.token_info = info.clone();
+                    info
+                };
+                sess.tx_event
+                    .send(Event {
+                        id: sub_id.to_string(),
+                        msg: EventMsg::TokenCount(crate::protocol::TokenCountEvent { info }),
+                    })
+                    .await
+                    .ok();
 
                 let unified_diff = turn_diff_tracker.get_unified_diff();
                 if let Ok(Some(unified_diff)) = unified_diff {
@@ -2841,13 +2851,21 @@ async fn drain_to_completed(
                 response_id: _,
                 token_usage,
             }) => {
-                // some providers don't return token usage, so we default
-                // TODO: consider approximate token usage
-                let token_usage = token_usage.unwrap_or_default();
+                let info = {
+                    let mut st = sess.state.lock_unchecked();
+                    let info = TokenUsageInfo::new_or_append(
+                        &st.token_info,
+                        &token_usage,
+                        turn_context.client.get_model_context_window(),
+                    );
+                    st.token_info = info.clone();
+                    info
+                };
+
                 sess.tx_event
                     .send(Event {
                         id: sub_id.to_string(),
-                        msg: EventMsg::TokenCount(token_usage),
+                        msg: EventMsg::TokenCount(crate::protocol::TokenCountEvent { info }),
                     })
                     .await
                     .ok();
diff --git a/codex-rs/exec/src/event_processor_with_human_output.rs b/codex-rs/exec/src/event_processor_with_human_output.rs
index 0ee60b93..3c639ad2 100644
--- a/codex-rs/exec/src/event_processor_with_human_output.rs
+++ b/codex-rs/exec/src/event_processor_with_human_output.rs
@@ -189,8 +189,14 @@ impl EventProcessor for EventProcessorWithHumanOutput {
                 }
                 return CodexStatus::InitiateShutdown;
             }
-            EventMsg::TokenCount(token_usage) => {
-                ts_println!(self, "tokens used: {}", token_usage.blended_total());
+            EventMsg::TokenCount(ev) => {
+                if let Some(usage_info) = ev.info {
+                    ts_println!(
+                        self,
+                        "tokens used: {}",
+                        usage_info.total_token_usage.blended_total()
+                    );
+                }
             }
             EventMsg::AgentMessageDelta(AgentMessageDeltaEvent { delta }) => {
                 if !self.answer_started {
diff --git a/codex-rs/protocol/src/protocol.rs b/codex-rs/protocol/src/protocol.rs
index 2308b7d2..a422327d 100644
--- a/codex-rs/protocol/src/protocol.rs
+++ b/codex-rs/protocol/src/protocol.rs
@@ -417,9 +417,9 @@ pub enum EventMsg {
     /// Agent has completed all actions
     TaskComplete(TaskCompleteEvent),
 
-    /// Token count event, sent periodically to report the number of tokens
-    /// used in the current session.
-    TokenCount(TokenUsage),
+    /// Usage update for the current session, including totals and last turn.
+    /// Optional means unknown — UIs should not display when `None`.
+    TokenCount(TokenCountEvent),
 
     /// Agent text output message
     AgentMessage(AgentMessageEvent),
@@ -521,12 +521,54 @@ pub struct TaskStartedEvent {
 #[derive(Debug, Clone, Deserialize, Serialize, Default)]
 pub struct TokenUsage {
     pub input_tokens: u64,
-    pub cached_input_tokens: Option<u64>,
+    pub cached_input_tokens: u64,
     pub output_tokens: u64,
-    pub reasoning_output_tokens: Option<u64>,
+    pub reasoning_output_tokens: u64,
     pub total_tokens: u64,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct TokenUsageInfo {
+    pub total_token_usage: TokenUsage,
+    pub last_token_usage: TokenUsage,
+    pub model_context_window: Option<u64>,
+}
+
+impl TokenUsageInfo {
+    pub fn new_or_append(
+        info: &Option<TokenUsageInfo>,
+        last: &Option<TokenUsage>,
+        model_context_window: Option<u64>,
+    ) -> Option<Self> {
+        if info.is_none() && last.is_none() {
+            return None;
+        }
+
+        let mut info = match info {
+            Some(info) => info.clone(),
+            None => Self {
+                total_token_usage: TokenUsage::default(),
+                last_token_usage: TokenUsage::default(),
+                model_context_window,
+            },
+        };
+        if let Some(last) = last {
+            info.append_last_usage(last);
+        }
+        Some(info)
+    }
+
+    pub fn append_last_usage(&mut self, last: &TokenUsage) {
+        self.total_token_usage.add_assign(last);
+        self.last_token_usage = last.clone();
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct TokenCountEvent {
+    pub info: Option<TokenUsageInfo>,
+}
+
 // Includes prompts, tools and space to call compact.
 const BASELINE_TOKENS: u64 = 12000;
 
@@ -536,7 +578,7 @@ impl TokenUsage {
     }
 
     pub fn cached_input(&self) -> u64 {
-        self.cached_input_tokens.unwrap_or(0)
+        self.cached_input_tokens
     }
 
     pub fn non_cached_input(&self) -> u64 {
@@ -554,7 +596,7 @@ impl TokenUsage {
     /// This will be off for the current turn and pending function calls.
     pub fn tokens_in_context_window(&self) -> u64 {
         self.total_tokens
-            .saturating_sub(self.reasoning_output_tokens.unwrap_or(0))
+            .saturating_sub(self.reasoning_output_tokens)
     }
 
     /// Estimate the remaining user-controllable percentage of the model's context window.
@@ -579,6 +621,15 @@ impl TokenUsage {
         let remaining = effective_window.saturating_sub(used);
         ((remaining as f32 / effective_window as f32) * 100.0).clamp(0.0, 100.0) as u8
     }
+
+    /// In-place element-wise sum of token counts.
+    pub fn add_assign(&mut self, other: &TokenUsage) {
+        self.input_tokens += other.input_tokens;
+        self.cached_input_tokens += other.cached_input_tokens;
+        self.output_tokens += other.output_tokens;
+        self.reasoning_output_tokens += other.reasoning_output_tokens;
+        self.total_tokens += other.total_tokens;
+    }
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize)]
@@ -606,10 +657,11 @@ impl fmt::Display for FinalOutput {
                 String::new()
             },
             token_usage.output_tokens,
-            token_usage
-                .reasoning_output_tokens
-                .map(|r| format!(" (reasoning {r})"))
-                .unwrap_or_default()
+            if token_usage.reasoning_output_tokens > 0 {
+                format!(" (reasoning {})", token_usage.reasoning_output_tokens)
+            } else {
+                String::new()
+            }
         )
     }
 }
diff --git a/codex-rs/tui/src/bottom_pane/chat_composer.rs b/codex-rs/tui/src/bottom_pane/chat_composer.rs
index 528290fa..aead743d 100644
--- a/codex-rs/tui/src/bottom_pane/chat_composer.rs
+++ b/codex-rs/tui/src/bottom_pane/chat_composer.rs
@@ -1,4 +1,4 @@
-use codex_core::protocol::TokenUsage;
+use codex_core::protocol::TokenUsageInfo;
 use crossterm::event::KeyCode;
 use crossterm::event::KeyEvent;
 use crossterm::event::KeyEventKind;
@@ -63,12 +63,6 @@ struct AttachedImage {
     path: PathBuf,
 }
 
-struct TokenUsageInfo {
-    total_token_usage: TokenUsage,
-    last_token_usage: TokenUsage,
-    model_context_window: Option<u64>,
-}
-
 pub(crate) struct ChatComposer {
     textarea: TextArea,
     textarea_state: RefCell<TextAreaState>,
@@ -166,17 +160,8 @@ impl ChatComposer {
     /// Update the cached *context-left* percentage and refresh the placeholder
     /// text. The UI relies on the placeholder to convey the remaining
     /// context when the composer is empty.
-    pub(crate) fn set_token_usage(
-        &mut self,
-        total_token_usage: TokenUsage,
-        last_token_usage: TokenUsage,
-        model_context_window: Option<u64>,
-    ) {
-        self.token_usage_info = Some(TokenUsageInfo {
-            total_token_usage,
-            last_token_usage,
-            model_context_window,
-        });
+    pub(crate) fn set_token_usage(&mut self, token_info: Option<TokenUsageInfo>) {
+        self.token_usage_info = token_info;
     }
 
     /// Record the history metadata advertised by `SessionConfiguredEvent` so
@@ -1290,11 +1275,16 @@ impl WidgetRef for ChatComposer {
                         } else {
                             100
                         };
+                        let context_style = if percent_remaining < 20 {
+                            Style::default().fg(Color::Yellow)
+                        } else {
+                            Style::default().add_modifier(Modifier::DIM)
+                        };
                         hint.push("   ".into());
-                        hint.push(
-                            Span::from(format!("{percent_remaining}% context left"))
-                                .style(Style::default().add_modifier(Modifier::DIM)),
-                        );
+                        hint.push(Span::styled(
+                            format!("{percent_remaining}% context left"),
+                            context_style,
+                        ));
                     }
                 }
 
diff --git a/codex-rs/tui/src/bottom_pane/mod.rs b/codex-rs/tui/src/bottom_pane/mod.rs
index d5daea2e..88b3f096 100644
--- a/codex-rs/tui/src/bottom_pane/mod.rs
+++ b/codex-rs/tui/src/bottom_pane/mod.rs
@@ -5,7 +5,7 @@ use crate::app_event_sender::AppEventSender;
 use crate::tui::FrameRequester;
 use crate::user_approval_widget::ApprovalRequest;
 use bottom_pane_view::BottomPaneView;
-use codex_core::protocol::TokenUsage;
+use codex_core::protocol::TokenUsageInfo;
 use codex_file_search::FileMatch;
 use crossterm::event::KeyEvent;
 use ratatui::buffer::Buffer;
@@ -358,14 +358,8 @@ impl BottomPane {
 
     /// Update the *context-window remaining* indicator in the composer. This
     /// is forwarded directly to the underlying `ChatComposer`.
-    pub(crate) fn set_token_usage(
-        &mut self,
-        total_token_usage: TokenUsage,
-        last_token_usage: TokenUsage,
-        model_context_window: Option<u64>,
-    ) {
-        self.composer
-            .set_token_usage(total_token_usage, last_token_usage, model_context_window);
+    pub(crate) fn set_token_usage(&mut self, token_info: Option<TokenUsageInfo>) {
+        self.composer.set_token_usage(token_info);
         self.request_redraw();
     }
 
diff --git a/codex-rs/tui/src/chatwidget.rs b/codex-rs/tui/src/chatwidget.rs
index 65ecbf74..bee9d5e1 100644
--- a/codex-rs/tui/src/chatwidget.rs
+++ b/codex-rs/tui/src/chatwidget.rs
@@ -29,6 +29,7 @@ use codex_core::protocol::PatchApplyBeginEvent;
 use codex_core::protocol::StreamErrorEvent;
 use codex_core::protocol::TaskCompleteEvent;
 use codex_core::protocol::TokenUsage;
+use codex_core::protocol::TokenUsageInfo;
 use codex_core::protocol::TurnAbortReason;
 use codex_core::protocol::TurnDiffEvent;
 use codex_core::protocol::UserMessageEvent;
@@ -109,8 +110,7 @@ pub(crate) struct ChatWidget {
     active_exec_cell: Option<ExecCell>,
     config: Config,
     initial_user_message: Option<UserMessage>,
-    total_token_usage: TokenUsage,
-    last_token_usage: TokenUsage,
+    token_info: Option<TokenUsageInfo>,
     // Stream lifecycle controller
     stream: StreamController,
     running_commands: HashMap<String, RunningCommand>,
@@ -259,16 +259,10 @@ impl ChatWidget {
         self.maybe_send_next_queued_input();
     }
 
-    fn on_token_count(&mut self, token_usage: TokenUsage) {
-        self.total_token_usage = add_token_usage(&self.total_token_usage, &token_usage);
-        self.last_token_usage = token_usage;
-        self.bottom_pane.set_token_usage(
-            self.total_token_usage.clone(),
-            self.last_token_usage.clone(),
-            self.config.model_context_window,
-        );
+    pub(crate) fn set_token_info(&mut self, info: Option<TokenUsageInfo>) {
+        self.bottom_pane.set_token_usage(info.clone());
+        self.token_info = info;
     }
-
     /// Finalize any active exec as failed, push an error message into history,
     /// and stop/clear running UI state.
     fn finalize_turn_with_error_message(&mut self, message: String) {
@@ -659,8 +653,7 @@ impl ChatWidget {
                 initial_prompt.unwrap_or_default(),
                 initial_images,
             ),
-            total_token_usage: TokenUsage::default(),
-            last_token_usage: TokenUsage::default(),
+            token_info: None,
             stream: StreamController::new(config),
             running_commands: HashMap::new(),
             task_complete_pending: false,
@@ -712,8 +705,7 @@ impl ChatWidget {
                 initial_prompt.unwrap_or_default(),
                 initial_images,
             ),
-            total_token_usage: TokenUsage::default(),
-            last_token_usage: TokenUsage::default(),
+            token_info: None,
             stream: StreamController::new(config),
             running_commands: HashMap::new(),
             task_complete_pending: false,
@@ -1050,7 +1042,7 @@ impl ChatWidget {
             EventMsg::AgentReasoningSectionBreak(_) => self.on_reasoning_section_break(),
             EventMsg::TaskStarted(_) => self.on_task_started(),
             EventMsg::TaskComplete(TaskCompleteEvent { .. }) => self.on_task_complete(),
-            EventMsg::TokenCount(token_usage) => self.on_token_count(token_usage),
+            EventMsg::TokenCount(ev) => self.set_token_info(ev.info),
             EventMsg::Error(ErrorEvent { message }) => self.on_error(message),
             EventMsg::TurnAborted(ev) => match ev.reason {
                 TurnAbortReason::Interrupted => {
@@ -1157,9 +1149,16 @@ impl ChatWidget {
     }
 
     pub(crate) fn add_status_output(&mut self) {
+        let default_usage;
+        let usage_ref = if let Some(ti) = &self.token_info {
+            &ti.total_token_usage
+        } else {
+            default_usage = TokenUsage::default();
+            &default_usage
+        };
         self.add_to_history(history_cell::new_status_output(
             &self.config,
-            &self.total_token_usage,
+            usage_ref,
             &self.session_id,
         ));
     }
@@ -1352,8 +1351,11 @@ impl ChatWidget {
         self.submit_user_message(text.into());
     }
 
-    pub(crate) fn token_usage(&self) -> &TokenUsage {
-        &self.total_token_usage
+    pub(crate) fn token_usage(&self) -> TokenUsage {
+        self.token_info
+            .as_ref()
+            .map(|ti| ti.total_token_usage.clone())
+            .unwrap_or_default()
     }
 
     pub(crate) fn session_id(&self) -> Option<Uuid> {
@@ -1367,12 +1369,8 @@ impl ChatWidget {
     }
 
     pub(crate) fn clear_token_usage(&mut self) {
-        self.total_token_usage = TokenUsage::default();
-        self.bottom_pane.set_token_usage(
-            self.total_token_usage.clone(),
-            self.last_token_usage.clone(),
-            self.config.model_context_window,
-        );
+        self.token_info = None;
+        self.bottom_pane.set_token_usage(None);
     }
 
     pub fn cursor_pos(&self, area: Rect) -> Option<(u16, u16)> {
@@ -1405,34 +1403,6 @@ const EXAMPLE_PROMPTS: [&str; 6] = [
     "Improve documentation in @filename",
 ];
 
-fn add_token_usage(current_usage: &TokenUsage, new_usage: &TokenUsage) -> TokenUsage {
-    let cached_input_tokens = match (
-        current_usage.cached_input_tokens,
-        new_usage.cached_input_tokens,
-    ) {
-        (Some(current), Some(new)) => Some(current + new),
-        (Some(current), None) => Some(current),
-        (None, Some(new)) => Some(new),
-        (None, None) => None,
-    };
-    let reasoning_output_tokens = match (
-        current_usage.reasoning_output_tokens,
-        new_usage.reasoning_output_tokens,
-    ) {
-        (Some(current), Some(new)) => Some(current + new),
-        (Some(current), None) => Some(current),
-        (None, Some(new)) => Some(new),
-        (None, None) => None,
-    };
-    TokenUsage {
-        input_tokens: current_usage.input_tokens + new_usage.input_tokens,
-        cached_input_tokens,
-        output_tokens: current_usage.output_tokens + new_usage.output_tokens,
-        reasoning_output_tokens,
-        total_tokens: current_usage.total_tokens + new_usage.total_tokens,
-    }
-}
-
 // Extract the first bold (Markdown) element in the form **...** from `s`.
 // Returns the inner text if found; otherwise `None`.
 fn extract_first_bold(s: &str) -> Option<String> {
diff --git a/codex-rs/tui/src/chatwidget/tests.rs b/codex-rs/tui/src/chatwidget/tests.rs
index 555ce50d..dfcbbec7 100644
--- a/codex-rs/tui/src/chatwidget/tests.rs
+++ b/codex-rs/tui/src/chatwidget/tests.rs
@@ -221,8 +221,7 @@ fn make_chatwidget_manual() -> (
         active_exec_cell: None,
         config: cfg.clone(),
         initial_user_message: None,
-        total_token_usage: TokenUsage::default(),
-        last_token_usage: TokenUsage::default(),
+        token_info: None,
         stream: StreamController::new(cfg),
         running_commands: HashMap::new(),
         task_complete_pending: false,
diff --git a/codex-rs/tui/src/history_cell.rs b/codex-rs/tui/src/history_cell.rs
index 7e1cf25e..c8fb5923 100644
--- a/codex-rs/tui/src/history_cell.rs
+++ b/codex-rs/tui/src/history_cell.rs
@@ -966,9 +966,8 @@ pub(crate) fn new_status_output(
         "  • Input: ".into(),
         usage.non_cached_input().to_string().into(),
     ];
-    if let Some(cached) = usage.cached_input_tokens
-        && cached > 0
-    {
+    if usage.cached_input_tokens > 0 {
+        let cached = usage.cached_input_tokens;
         input_line_spans.push(format!(" (+ {cached} cached)").into());
     }
     lines.push(Line::from(input_line_spans));