diff --git a/packages/eve/src/client/eve-agent-store.ts b/packages/eve/src/client/eve-agent-store.ts
index 9fc73a22d..9a224e3bc 100644
--- a/packages/eve/src/client/eve-agent-store.ts
+++ b/packages/eve/src/client/eve-agent-store.ts
@@ -173,6 +173,14 @@ export class EveAgentStore<TData> {
         signal: createAbortSignal(preparedInput.signal, abortController.signal),
       });
 
+      if (!this.#isCurrentOperation(operationId)) {
+        return;
+      }
+
+      // Eagerly notify listeners of the session ID before streaming begins.
+      this.#callbacks.onSessionChange?.(this.#session.state);
+      this.#publish();
+
       let sawEvent = false;
       for await (const event of response) {
         if (!this.#isCurrentOperation(operationId)) {
diff --git a/packages/eve/src/client/session.ts b/packages/eve/src/client/session.ts
index d839259ce..0754e3f99 100644
--- a/packages/eve/src/client/session.ts
+++ b/packages/eve/src/client/session.ts
@@ -72,6 +72,12 @@ export class ClientSession {
     const postResult = await this.#postTurn(payload, state);
     const { continuationToken, sessionId } = postResult;
 
+    // Eagerly surface the session ID so callers can read it from
+    // `session.state` before the event stream is consumed.
+    if (sessionId !== state.sessionId) {
+      this.#state = { ...state, sessionId };
+    }
+
     return new MessageResponse<TOutput>({
       continuationToken,
       createStream: () => this.#createEventStream(sessionId, continuationToken, state, payload),