diff --git a/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISession.aidl b/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISession.aidl
index 205429b..9033989 100644
--- a/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISession.aidl
+++ b/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISession.aidl
@@ -34,17 +34,17 @@
 package android.hardware.biometrics.face;
 @VintfStability
 interface ISession {
-  void generateChallenge(in int cookie);
-  void revokeChallenge(in int cookie, in long challenge);
-  android.hardware.biometrics.common.ICancellationSignal enroll(in int cookie, in android.hardware.keymaster.HardwareAuthToken hat, in android.hardware.biometrics.face.EnrollmentType type, in android.hardware.biometrics.face.Feature[] features, in android.hardware.common.NativeHandle previewSurface);
-  android.hardware.biometrics.common.ICancellationSignal authenticate(in int cookie, in long operationId);
-  android.hardware.biometrics.common.ICancellationSignal detectInteraction(in int cookie);
-  void enumerateEnrollments(in int cookie);
-  void removeEnrollments(in int cookie, in int[] enrollmentIds);
-  void getFeatures(in int cookie, in int enrollmentId);
-  void setFeature(in int cookie, in android.hardware.keymaster.HardwareAuthToken hat, in int enrollmentId, in android.hardware.biometrics.face.Feature feature, boolean enabled);
-  void getAuthenticatorId(in int cookie);
-  void invalidateAuthenticatorId(in int cookie);
-  void resetLockout(in int cookie, in android.hardware.keymaster.HardwareAuthToken hat);
-  void close(in int cookie);
+  void generateChallenge();
+  void revokeChallenge(in long challenge);
+  android.hardware.biometrics.common.ICancellationSignal enroll(in android.hardware.keymaster.HardwareAuthToken hat, in android.hardware.biometrics.face.EnrollmentType type, in android.hardware.biometrics.face.Feature[] features, in android.hardware.common.NativeHandle previewSurface);
+  android.hardware.biometrics.common.ICancellationSignal authenticate(in long operationId);
+  android.hardware.biometrics.common.ICancellationSignal detectInteraction();
+  void enumerateEnrollments();
+  void removeEnrollments(in int[] enrollmentIds);
+  void getFeatures(in int enrollmentId);
+  void setFeature(in android.hardware.keymaster.HardwareAuthToken hat, in int enrollmentId, in android.hardware.biometrics.face.Feature feature, boolean enabled);
+  void getAuthenticatorId();
+  void invalidateAuthenticatorId();
+  void resetLockout(in android.hardware.keymaster.HardwareAuthToken hat);
+  void close();
 }
diff --git a/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISessionCallback.aidl b/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISessionCallback.aidl
index b0bfa30..2bb053a 100644
--- a/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISessionCallback.aidl
+++ b/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/ISessionCallback.aidl
@@ -34,7 +34,6 @@
 package android.hardware.biometrics.face;
 @VintfStability
 interface ISessionCallback {
-  void onStateChanged(in int cookie, in android.hardware.biometrics.face.SessionState state);
   void onChallengeGenerated(in long challenge);
   void onChallengeRevoked(in long challenge);
   void onAuthenticationFrame(in android.hardware.biometrics.face.AuthenticationFrame frame);
diff --git a/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/SessionState.aidl b/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/SessionState.aidl
deleted file mode 100644
index 4db47c9..0000000
--- a/biometrics/face/aidl/aidl_api/android.hardware.biometrics.face/current/android/hardware/biometrics/face/SessionState.aidl
+++ /dev/null
@@ -1,51 +0,0 @@
-/*
- * Copyright (C) 2021 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-///////////////////////////////////////////////////////////////////////////////
-// THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
-///////////////////////////////////////////////////////////////////////////////
-
-// This file is a snapshot of an AIDL file. Do not edit it manually. There are
-// two cases:
-// 1). this is a frozen version file - do not edit this in any case.
-// 2). this is a 'current' file. If you make a backwards compatible change to
-//     the interface (from the latest frozen version), the build system will
-//     prompt you to update this file with `m <name>-update-api`.
-//
-// You must not make a backward incompatible change to any AIDL file built
-// with the aidl_interface module type with versions property set. The module
-// type is used to build AIDL files in a way that they can be used across
-// independently updatable components of the system. If a device is shipped
-// with such a backward incompatible change, it has a high risk of breaking
-// later when a module using the interface is updated, e.g., Mainline modules.
-
-package android.hardware.biometrics.face;
-@Backing(type="byte") @VintfStability
-enum SessionState {
-  IDLING = 0,
-  CLOSED = 1,
-  GENERATING_CHALLENGE = 2,
-  REVOKING_CHALLENGE = 3,
-  ENROLLING = 4,
-  AUTHENTICATING = 5,
-  DETECTING_INTERACTION = 6,
-  ENUMERATING_ENROLLMENTS = 7,
-  REMOVING_ENROLLMENTS = 8,
-  GETTING_FEATURES = 9,
-  SETTING_FEATURE = 10,
-  GETTING_AUTHENTICATOR_ID = 11,
-  INVALIDATING_AUTHENTICATOR_ID = 12,
-  RESETTING_LOCKOUT = 13,
-}
diff --git a/biometrics/face/aidl/android/hardware/biometrics/face/ISession.aidl b/biometrics/face/aidl/android/hardware/biometrics/face/ISession.aidl
index 66c7c38..7502515 100644
--- a/biometrics/face/aidl/android/hardware/biometrics/face/ISession.aidl
+++ b/biometrics/face/aidl/android/hardware/biometrics/face/ISession.aidl
@@ -23,11 +23,25 @@
 import android.hardware.keymaster.HardwareAuthToken;
 
 /**
- * A session is a collection of immutable state (sensorId, userId), mutable state (SessionState),
- * methods available for the framework to call, and a callback (ISessionCallback) to notify the
- * framework about the events and results. A session is used to establish communication between
- * the framework and the HAL.
+ * Operations that can be performed for unique sessions retrieved via IFace#createSession.
+ * Operations defined within this interface can be divided into the following categories:
+ * 1) Cancellable operations. These are usually the operations that can execute for several
+ *     minutes. To allow for cancellation, they return an instance of ICancellationSignal that
+ *     lets the framework cancel them by calling ICancellationSignal#cancel. If such an operation
+ *     is cancelled, it must notify the framework by calling ISessionCallback#onError with
+ *     Error::CANCELED.
+ * 2) Non-cancellable operations. Such operations cannot be cancelled once started.
+ *
+ * The lifecycle of an operation ends when one of its terminal callbacks is called. For example,
+ * ISession#authenticate is considered completed when any of the following callbacks is called:
+ * ISessionCallback#onError, ISessionCallback#onAuthenticationSucceeded,
+ * ISessionCallback#onAuthenticationFailed.
+ *
+ * ISession only supports execution of one operation at a time, regardless of whether it's
+ * cancellable or not. The framework must wait for a corresponding callback indicating the end of
+ * the current operation before a new operation can be started.
  */
+
 @VintfStability
 interface ISession {
     /**
@@ -68,9 +82,8 @@
      * | 0        | 10     | <Time4>    | <Random4> |
      * ----------------------------------------------
      *
-     * @param cookie A unique number identifying this operation
      */
-    void generateChallenge(in int cookie);
+    void generateChallenge();
 
     /**
      * revokeChallenge:
@@ -79,10 +92,9 @@
      * parameters is requested, the implementation must still notify the framework using the
      * provided callback.
      *
-     * @param cookie A unique number identifying this operation
      * @param challenge Challenge that should be revoked.
      */
-    void revokeChallenge(in int cookie, in long challenge);
+    void revokeChallenge(in long challenge);
 
     /**
      * getEnrollmentConfig:
@@ -101,19 +113,13 @@
      *
      * A request to add a face enrollment.
      *
-     * Once the HAL is able to start processing the enrollment request, it must notify the framework
-     * via ISessionCallback#onStateChanged with SessionState::ENROLLING.
-     *
      * At any point during enrollment, if a non-recoverable error occurs, the HAL must notify the
-     * framework via ISessionCallback#onError with the applicable enrollment-specific error, and
-     * then send ISessionCallback#onStateChanged(cookie, SessionState::IDLING) if no subsequent
-     * operation is in the queue.
+     * framework via ISessionCallback#onError with the applicable enrollment-specific error.
      *
      * Before capturing face data, the implementation must first verify the authenticity and
      * integrity of the provided HardwareAuthToken. In addition, it must check that the challenge
      * within the provided HardwareAuthToken is valid. See ISession#generateChallenge. If any of
-     * the above checks fail, the framework must be notified via ISessionCallback#onError and the
-     * HAL must notify the framework when it returns to the idle state. See
+     * the above checks fail, the framework must be notified using ISessionCallback#onError with
      * Error::UNABLE_TO_PROCESS.
      *
      * During enrollment, the implementation may notify the framework via
@@ -121,15 +127,12 @@
      * can be invoked multiple times if necessary. Similarly, the framework may be notified of
      * enrollment progress changes via ISessionCallback#onEnrollmentProgress. Once the framework is
      * notified that there are 0 "remaining" steps, the framework may cache the "enrollmentId". See
-     * ISessionCallback#onEnrollmentProgress for more info. The HAL must notify the framework once
-     * it returns to the idle state.
+     * ISessionCallback#onEnrollmentProgress for more info.
      *
-     * When a finger is successfully added and before the framework is notified of remaining=0, the
-     * implementation MUST update and associate this (sensorId, userId) pair with a new new
+     * When a face is successfully added and before the framework is notified of remaining=0, the
+     * implementation MUST update and associate this (sensorId, userId) pair with a new
      * entropy-encoded random identifier. See ISession#getAuthenticatorId for more information.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param hat See above documentation.
      * @param enrollmentType See the EnrollmentType enum.
      * @param features See the Feature enum.
@@ -139,7 +142,7 @@
      * @return ICancellationSignal An object that can be used by the framework to cancel this
      * operation.
      */
-    ICancellationSignal enroll(in int cookie, in HardwareAuthToken hat, in EnrollmentType type,
+    ICancellationSignal enroll(in HardwareAuthToken hat, in EnrollmentType type,
             in Feature[] features, in NativeHandle previewSurface);
 
     /**
@@ -147,13 +150,8 @@
      *
      * A request to start looking for faces to authenticate.
      *
-     * Once the HAL is able to start processing the authentication request, it must notify framework
-     * via ISessionCallback#onStateChanged with SessionState::AUTHENTICATING.
-     *
      * At any point during authentication, if a non-recoverable error occurs, the HAL must notify
-     * the framework via ISessionCallback#onError with the applicable authentication-specific error,
-     * and then send ISessionCallback#onStateChanged(cookie, SessionState::IDLING) if no
-     * subsequent operation is in the queue.
+     * the framework via ISessionCallback#onError with the applicable authentication-specific error.
      *
      * During authentication, the implementation may notify the framework via
      * ISessionCallback#onAcquired with messages that may be used to guide the user. This callback
@@ -175,8 +173,6 @@
      * must be set with the operationId passed in during #authenticate. If the sensor is NOT
      * SensorStrength::STRONG, the HardwareAuthToken MUST be null.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param operationId For sensors configured as SensorStrength::STRONG, this must be used ONLY
      *                    upon successful authentication and wrapped in the HardwareAuthToken's
      *                    "challenge" field and sent to the framework via
@@ -190,7 +186,7 @@
      * @return ICancellationSignal An object that can be used by the framework to cancel this
      * operation.
      */
-    ICancellationSignal authenticate(in int cookie, in long operationId);
+    ICancellationSignal authenticate(in long operationId);
 
     /**
      * detectInteraction:
@@ -199,17 +195,12 @@
      * SensorProps#supportsDetectInteraction is true. If invoked on implementations that do not
      * support this functionality, the HAL must respond with ISession#onError(UNABLE_TO_PROCESS, 0).
      *
-     * Once the HAL is able to start processing this request, it must notify the framework via
-     * ISessionCallback#onStateChanged with SessionState::DETECTING_INTERACTION.
-     *
      * The framework will use this method in cases where determing user presence is required, but
      * identifying/authentication is not. For example, when the device is encrypted (first boot) or
      * in lockdown mode.
      *
      * At any point during detectInteraction, if a non-recoverable error occurs, the HAL must notify
-     * the framework via ISessionCallback#onError with the applicable error, and then send
-     * ISessionCallback#onStateChanged(cookie, SessionState::IDLING) if no subsequent operation is
-     * in the queue.
+     * the framework via ISessionCallback#onError with the applicable error.
      *
      * The implementation must only check for a face-like image was detected (e.g. to
      * minimize interactions due to non-face objects), and the lockout counter must not
@@ -222,17 +213,14 @@
      * 1) Any face is detected and the framework is notified via
      *    ISessionCallback#onInteractiondetected
      * 2) The operation was cancelled by the framework (see ICancellationSignal)
-     * 3) The HAL ends the operation, for example when a subsequent operation pre-empts this one.
      *
      * Note that if the operation is canceled, the implementation must notify the framework via
      * ISessionCallback#onError with Error::CANCELED.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path.
-     *               The framework will guarantee that it is unique per ISession.
      * @return ICancellationSignal An object that can be used by the framework to cancel this
      * operation.
      */
-    ICancellationSignal detectInteraction(in int cookie);
+    ICancellationSignal detectInteraction();
 
     /*
      * enumerateEnrollments:
@@ -240,32 +228,22 @@
      * A request to enumerate (list) the enrollments for this (sensorId, userId) pair. The
      * framework typically uses this to ensure that its cache is in sync with the HAL.
      *
-     * Once the HAL is able to start processing this request, it must notify the framework via
-     * ISessionCallback#onStateChanged with SessionState::ENUMERATING_ENROLLMENTS.
-     *
      * The implementation must then notify the framework with a list of enrollments applicable
      * for the current session via ISessionCallback#onEnrollmentsEnumerated.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path.
-     *               The framework will guarantee that it is unique per ISession.
      */
-    void enumerateEnrollments(in int cookie);
+    void enumerateEnrollments();
 
     /**
      * removeEnrollments:
      *
      * A request to remove the enrollments for this (sensorId, userId) pair.
      *
-     * Once the HAL is able to start processing this request, it must notify the framework via
-     * ISessionCallback#onStateChanged with SessionState::REMOVING_ENROLLMENTS.
-     *
      * After removing the enrollmentIds from everywhere necessary (filesystem, secure subsystems,
      * etc), the implementation must notify the framework via ISessionCallback#onEnrollmentsRemoved.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path.
-     *               The framework will guarantee that it is unique per ISession.
      */
-    void removeEnrollments(in int cookie, in int[] enrollmentIds);
+    void removeEnrollments(in int[] enrollmentIds);
 
     /**
      * getFeatures:
@@ -273,20 +251,14 @@
      * Returns a list of currently enabled features for the provided enrollmentId.
      *
      * If the enrollmentId is invalid, the HAL must invoke ISessionCallback#onError with
-     * Error::UNABLE_TO_PROCESS and return to SessionState::IDLING if no subsequent work is in the
-     * queue.
-     *
-     * Once the HAL is able to start processing this request, it must notify the framework by using
-     * ISessionCallback#onStateChanged with SessionState::GETTING_FEATURES.
+     * Error::UNABLE_TO_PROCESS.
      *
      * The HAL must notify the framework about the result by calling
      * ISessionCallback#onFeaturesRetrieved.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param enrollmentId the ID of the enrollment for which the features are requested.
      */
-    void getFeatures(in int cookie, in int enrollmentId);
+    void getFeatures(in int enrollmentId);
 
     /**
      * setFeature:
@@ -296,24 +268,18 @@
      * (see @param hat). The HAL must verify the hat before changing any feature state.
      *
      * If either the hat or enrollmentId is invalid, the HAL must invoke ISessionCallback#onError
-     * with Error::UNABLE_TO_PROCESS and return to SessionState::IDLING if no subsequent work is in
-     * the queue.
-     *
-     * Once the HAL is able to start processing this request, it must notify the framework by using
-     * ISessionCallback#onStateChanged with SessionState::SETTING_FEATURE.
+     * with Error::UNABLE_TO_PROCESS.
      *
      * After the feature is successfully set, the HAL must notify the framework by calling
      * ISessionCallback#onFeatureSet.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param hat HardwareAuthToken See above documentation.
      * @param enrollmentId the ID of the enrollment for which the feature update is requested.
      * @param feature The feature to be enabled or disabled.
      * @param enabled Whether the provided features should be enabled or disabled.
      */
-    void setFeature(in int cookie, in HardwareAuthToken hat, in int enrollmentId,
-            in Feature feature, boolean enabled);
+    void setFeature(
+            in HardwareAuthToken hat, in int enrollmentId, in Feature feature, boolean enabled);
 
     /**
      * getAuthenticatorId:
@@ -341,10 +307,8 @@
      *   3) MUST not change if a face is deleted.
      *   4) MUST be an entropy-encoded random number
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      */
-    void getAuthenticatorId(in int cookie);
+    void getAuthenticatorId();
 
     /**
      * invalidateAuthenticatorId:
@@ -368,10 +332,8 @@
      * for more details). As such, the framework would coordinate invalidation across multiple
      * biometric HALs as necessary.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      */
-    void invalidateAuthenticatorId(in int cookie);
+    void invalidateAuthenticatorId();
 
     /**
      * resetLockout:
@@ -382,8 +344,7 @@
      *   2) Verify that the timestamp provided within the HAT is relatively recent (e.g. on the
      *      order of minutes, not hours).
      * If either of the checks fail, the HAL must invoke ISessionCallback#onError with
-     * Error::UNABLE_TO_PROCESS and return to SessionState::IDLING if no subsequent work is in the
-     * queue.
+     * Error::UNABLE_TO_PROCESS.
      *
      * Upon successful verification, the HAL must clear the lockout counter and notify the framework
      * via ISessionCallback#onLockoutCleared.
@@ -414,27 +375,20 @@
      * See the Android CDD section 7.3.10 for the full set of lockout and rate-limiting
      * requirements.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param hat HardwareAuthToken See above documentation.
      */
-    void resetLockout(in int cookie, in HardwareAuthToken hat);
+    void resetLockout(in HardwareAuthToken hat);
 
     /*
      * Close this session and allow the HAL to release the resources associated with this session.
      *
-     * A session can only be closed when it's in SessionState::IDLING. Closing a session will
-     * result in a ISessionCallback#onStateChanged call with SessionState::CLOSED.
-     *
-     * If a session is unresponsive or stuck in a state other than SessionState::CLOSED,
-     * IFace#reset could be used as a last resort to terminate the session and recover the HAL
-     * from a bad state.
+     * A session can only be closed when the HAL is idling, i.e. not performing any operations.
+     * If the HAL is busy performing a cancellable operation, the operation must be explicitly
+     * cancelled with a call to ICancellationSignal#cancel before the session can be closed.
      *
      * All sessions must be explicitly closed. Calling IFace#createSession while there is an active
      * session is considered an error.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      */
-    void close(in int cookie);
+    void close();
 }
diff --git a/biometrics/face/aidl/android/hardware/biometrics/face/ISessionCallback.aidl b/biometrics/face/aidl/android/hardware/biometrics/face/ISessionCallback.aidl
index c1aa3fc..a2601e7 100644
--- a/biometrics/face/aidl/android/hardware/biometrics/face/ISessionCallback.aidl
+++ b/biometrics/face/aidl/android/hardware/biometrics/face/ISessionCallback.aidl
@@ -21,17 +21,11 @@
 import android.hardware.biometrics.face.EnrollmentFrame;
 import android.hardware.biometrics.face.Error;
 import android.hardware.biometrics.face.Feature;
-import android.hardware.biometrics.face.SessionState;
 import android.hardware.keymaster.HardwareAuthToken;
 
 @VintfStability
 interface ISessionCallback {
     /**
-     * Used to notify the framework of session state changes. See ISession for more information.
-     */
-    void onStateChanged(in int cookie, in SessionState state);
-
-    /**
      * Notifies the framework when a challenge is successfully generated.
      */
     void onChallengeGenerated(in long challenge);
@@ -42,9 +36,9 @@
     void onChallengeRevoked(in long challenge);
 
     /**
-     * This method must only be used to notify the framework during the following states:
-     *   1) SessionState::AUTHENTICATING
-     *   2) SessionState::DETECTING_INTERACTION
+     * This method must only be used to notify the framework during the following operations:
+     *   1) ISession#authenticate
+     *   2) ISession#detectInteraction
      *
      * These messages may be used to provide user guidance multiple times if necessary per
      * operation.
@@ -54,8 +48,8 @@
     void onAuthenticationFrame(in AuthenticationFrame frame);
 
     /**
-     * This method must only be used to notify the framework during the SessionState::ENROLLING
-     * state.
+     * This method must only be used to notify the framework during the ISession#enroll
+     * operation.
      *
      * These messages may be used to provide user guidance multiple times if necessary per
      * operation.
@@ -65,18 +59,18 @@
     void onEnrollmentFrame(in EnrollmentFrame frame);
 
     /**
-     * This method must only be used to notify the framework during the following states:
-     *   1) SessionState::ENROLLING
-     *   2) SessionState::AUTHENTICATING
-     *   3) SessionState::DETECTING_INTERACTION
-     *   4) SessionState::INVALIDATING_AUTHENTICATOR_ID
-     *   5) SessionState::RESETTING_LOCKOUT
+     * This method must only be used to notify the framework during the following operations:
+     *   1) ISession#enroll
+     *   2) ISession#authenticate
+     *   3) ISession#detectInteraction
+     *   4) ISession#invalidateAuthenticatorId
+     *   5) ISession#resetLockout
      *
      * These messages may be used to notify the framework or user that a non-recoverable error
      * has occurred. The operation is finished, and the HAL must proceed with the next operation
-     * or return to SessionState::IDLING if the queue is empty.
+     * or return to the idling state.
      *
-     * Note that cancellation (see common::ICancellationSignal) and preemption most be followed with
+     * Note that cancellation (see common::ICancellationSignal) and preemption must be followed with
      * an Error::CANCELED message.
      *
      * @param error See the Error enum.
@@ -88,8 +82,7 @@
     void onError(in Error error, in int vendorCode);
 
     /**
-     * This method must only be used to notify the framework during the following state:
-     *   1) SessionState::ENROLLING
+     * This method must only be used to notify the framework during the ISession#enroll operation.
      *
      * @param enrollmentId Unique stable identifier for the enrollment that's being added by this
      *                     ISession#enroll invocation.
@@ -98,7 +91,7 @@
     void onEnrollmentProgress(in int enrollmentId, int remaining);
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Used to notify the framework about a successful authentication. This ends the authentication
      * lifecycle.
@@ -112,7 +105,7 @@
     void onAuthenticationSucceeded(in int enrollmentId, in HardwareAuthToken hat);
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Used to notify the framework about a failed authentication. This ends the authentication
      * lifecycle.
@@ -120,7 +113,7 @@
     void onAuthenticationFailed();
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Authentication is locked out due to too many unsuccessful attempts. This is a rate-limiting
      * lockout, and authentication can be restarted after a period of time. See
@@ -133,7 +126,7 @@
     void onLockoutTimed(in long durationMillis);
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Authentication is disabled until the user unlocks with their device credential
      * (PIN/Pattern/Password). See ISession#resetLockout.
@@ -160,7 +153,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::DETECTING_INTERACTION
+     * ISession#detectInteraction
      *
      * Notifies the framework that user interaction occurred. See ISession#detectInteraction.
      */
@@ -168,7 +161,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::ENUMERATING_ENROLLMENTS.
+     * ISession#enumerateEnrollments.
      *
      * Notifies the framework of the current enrollments. See ISession#enumerateEnrollments.
      *
@@ -177,7 +170,7 @@
     void onEnrollmentsEnumerated(in int[] enrollmentIds);
 
     /**
-     * This method must only be used to notify the framework during SessionState::GETTING_FEATURES.
+     * This method must only be used to notify the framework during ISession#getFeatures.
      *
      * Provides a list of features that are currently enabled for the given enrollmentId.
      *
@@ -187,7 +180,7 @@
     void onFeaturesRetrieved(in Feature[] features, in int enrollmentId);
 
     /**
-     * This method must only be used to notify the framework during SessionState::SETTING_FEATURE.
+     * This method must only be used to notify the framework during ISession#setFeature.
      *
      * Notifies the framework that ISession#setFeature has completed.
      *
@@ -198,7 +191,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::REMOVING_ENROLLMENTS.
+     * ISession#removeEnrollments.
      *
      * Notifies the framework that the specified enrollments are removed.
      *
@@ -208,7 +201,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::GETTING_AUTHENTICATOR_ID.
+     * ISession#getAuthenticatorId.
      *
      * Notifies the framework with the authenticatorId corresponding to this session's
      * (userId, sensorId) pair.
@@ -219,7 +212,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::INVALIDATING_AUTHENTICATOR_ID.
+     * ISession#invalidateAuthenticatorId.
      *
      * See ISession#invalidateAuthenticatorId for more information.
      *
diff --git a/biometrics/face/aidl/android/hardware/biometrics/face/SessionState.aidl b/biometrics/face/aidl/android/hardware/biometrics/face/SessionState.aidl
deleted file mode 100644
index afde4eb..0000000
--- a/biometrics/face/aidl/android/hardware/biometrics/face/SessionState.aidl
+++ /dev/null
@@ -1,91 +0,0 @@
-/*
- * Copyright (C) 2021 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package android.hardware.biometrics.face;
-
-@VintfStability
-@Backing(type="byte")
-enum SessionState {
-    /**
-     * The HAL is not processing any session requests.
-     */
-    IDLING,
-
-    /**
-     * The session has been closed by the client.
-     */
-    CLOSED,
-
-    /**
-     * The HAL is processing the ISession#generateChallenge request.
-     */
-    GENERATING_CHALLENGE,
-
-    /**
-     * The HAL is processing the ISession#revokeChallenge request.
-     */
-    REVOKING_CHALLENGE,
-
-    /**
-     * The HAL is processing the ISession#enroll request.
-     */
-    ENROLLING,
-
-    /**
-     * The HAL is processing the ISession#authenticate request.
-     */
-    AUTHENTICATING,
-
-    /**
-     * The HAL is processing the ISession#detectInteraction request.
-     */
-    DETECTING_INTERACTION,
-
-    /**
-     * The HAL is processing the ISession#enumerateEnrollments request.
-     */
-    ENUMERATING_ENROLLMENTS,
-
-    /**
-     * The HAL is processing the ISession#removeEnrollments request.
-     */
-    REMOVING_ENROLLMENTS,
-
-    /**
-     * The HAL is processing the ISession#getFeatures request.
-     */
-    GETTING_FEATURES,
-
-    /**
-     * The HAL is processing the ISession#setFeature request.
-     */
-    SETTING_FEATURE,
-
-    /**
-     * The HAL is processing the ISession#getAuthenticatorId request.
-     */
-    GETTING_AUTHENTICATOR_ID,
-
-    /**
-     * The HAL is processing the ISession#invalidateAuthenticatorId request.
-     */
-    INVALIDATING_AUTHENTICATOR_ID,
-
-    /**
-     * The HAL is processing the ISession#resetLockout request.
-     */
-    RESETTING_LOCKOUT
-}
diff --git a/biometrics/face/aidl/default/Session.cpp b/biometrics/face/aidl/default/Session.cpp
index ce6c557..b5eb717 100644
--- a/biometrics/face/aidl/default/Session.cpp
+++ b/biometrics/face/aidl/default/Session.cpp
@@ -30,119 +30,105 @@
 
     ndk::ScopedAStatus cancel() override {
         cb_->onError(Error::CANCELED, 0 /* vendorCode */);
-        cb_->onStateChanged(0, SessionState::IDLING);
         return ndk::ScopedAStatus::ok();
     }
 };
 
 Session::Session(std::shared_ptr<ISessionCallback> cb) : cb_(std::move(cb)) {}
 
-ndk::ScopedAStatus Session::generateChallenge(int32_t /*cookie*/) {
+ndk::ScopedAStatus Session::generateChallenge() {
     LOG(INFO) << "generateChallenge";
     if (cb_) {
-        cb_->onStateChanged(0, SessionState::GENERATING_CHALLENGE);
         cb_->onChallengeGenerated(0);
-        cb_->onStateChanged(0, SessionState::IDLING);
     }
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::revokeChallenge(int32_t /*cookie*/, int64_t challenge) {
+ndk::ScopedAStatus Session::revokeChallenge(int64_t challenge) {
     LOG(INFO) << "revokeChallenge";
     if (cb_) {
-        cb_->onStateChanged(0, SessionState::REVOKING_CHALLENGE);
         cb_->onChallengeRevoked(challenge);
-        cb_->onStateChanged(0, SessionState::IDLING);
     }
     return ndk::ScopedAStatus::ok();
 }
 
 ndk::ScopedAStatus Session::enroll(
-        int32_t /*cookie*/, const keymaster::HardwareAuthToken& /*hat*/,
-        EnrollmentType /*enrollmentType*/, const std::vector<Feature>& /*features*/,
-        const NativeHandle& /*previewSurface*/,
+        const keymaster::HardwareAuthToken& /*hat*/, EnrollmentType /*enrollmentType*/,
+        const std::vector<Feature>& /*features*/, const NativeHandle& /*previewSurface*/,
         std::shared_ptr<biometrics::common::ICancellationSignal>* /*return_val*/) {
     LOG(INFO) << "enroll";
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::authenticate(int32_t /*cookie*/, int64_t /*keystoreOperationId*/,
+ndk::ScopedAStatus Session::authenticate(int64_t /*keystoreOperationId*/,
                                          std::shared_ptr<common::ICancellationSignal>* return_val) {
     LOG(INFO) << "authenticate";
     if (cb_) {
-        cb_->onStateChanged(0, SessionState::AUTHENTICATING);
+        cb_->onError(Error::UNABLE_TO_PROCESS, 0 /* vendorCode */);
     }
     *return_val = SharedRefBase::make<CancellationSignal>(cb_);
     return ndk::ScopedAStatus::ok();
 }
 
 ndk::ScopedAStatus Session::detectInteraction(
-        int32_t /*cookie*/, std::shared_ptr<common::ICancellationSignal>* /*return_val*/) {
+        std::shared_ptr<common::ICancellationSignal>* /*return_val*/) {
     LOG(INFO) << "detectInteraction";
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::enumerateEnrollments(int32_t /*cookie*/) {
+ndk::ScopedAStatus Session::enumerateEnrollments() {
     LOG(INFO) << "enumerateEnrollments";
     if (cb_) {
-        cb_->onStateChanged(0, SessionState::ENUMERATING_ENROLLMENTS);
         cb_->onEnrollmentsEnumerated(std::vector<int32_t>());
-        cb_->onStateChanged(0, SessionState::IDLING);
     }
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::removeEnrollments(int32_t /*cookie*/,
-                                              const std::vector<int32_t>& /*enrollmentIds*/) {
+ndk::ScopedAStatus Session::removeEnrollments(const std::vector<int32_t>& /*enrollmentIds*/) {
     LOG(INFO) << "removeEnrollments";
     if (cb_) {
-        cb_->onStateChanged(0, SessionState::REMOVING_ENROLLMENTS);
         cb_->onEnrollmentsRemoved(std::vector<int32_t>());
-        cb_->onStateChanged(0, SessionState::IDLING);
     }
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::getFeatures(int32_t /*cookie*/, int32_t /*enrollmentId*/) {
+ndk::ScopedAStatus Session::getFeatures(int32_t /*enrollmentId*/) {
     LOG(INFO) << "getFeatures";
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::setFeature(int32_t /*cookie*/,
-                                       const keymaster::HardwareAuthToken& /*hat*/,
+ndk::ScopedAStatus Session::setFeature(const keymaster::HardwareAuthToken& /*hat*/,
                                        int32_t /*enrollmentId*/, Feature /*feature*/,
                                        bool /*enabled*/) {
     LOG(INFO) << "setFeature";
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::getAuthenticatorId(int32_t /*cookie*/) {
+ndk::ScopedAStatus Session::getAuthenticatorId() {
     LOG(INFO) << "getAuthenticatorId";
     if (cb_) {
-        cb_->onStateChanged(0, SessionState::GETTING_AUTHENTICATOR_ID);
         cb_->onAuthenticatorIdRetrieved(0 /* authenticatorId */);
-        cb_->onStateChanged(0, SessionState::IDLING);
     }
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::invalidateAuthenticatorId(int32_t /*cookie*/) {
+ndk::ScopedAStatus Session::invalidateAuthenticatorId() {
     LOG(INFO) << "invalidateAuthenticatorId";
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::resetLockout(int32_t /*cookie*/,
-                                         const keymaster::HardwareAuthToken& /*hat*/) {
+ndk::ScopedAStatus Session::resetLockout(const keymaster::HardwareAuthToken& /*hat*/) {
     LOG(INFO) << "resetLockout";
     if (cb_) {
-        cb_->onStateChanged(0, SessionState::RESETTING_LOCKOUT);
         cb_->onLockoutCleared();
-        cb_->onStateChanged(0, SessionState::IDLING);
     }
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::close(int32_t /*cookie*/) {
+ndk::ScopedAStatus Session::close() {
+    if (cb_) {
+        cb_->onSessionClosed();
+    }
     return ndk::ScopedAStatus::ok();
 }
 
diff --git a/biometrics/face/aidl/default/Session.h b/biometrics/face/aidl/default/Session.h
index eb9ae83..73cdf08 100644
--- a/biometrics/face/aidl/default/Session.h
+++ b/biometrics/face/aidl/default/Session.h
@@ -30,40 +30,38 @@
   public:
     explicit Session(std::shared_ptr<ISessionCallback> cb);
 
-    ndk::ScopedAStatus generateChallenge(int32_t cookie) override;
+    ndk::ScopedAStatus generateChallenge() override;
 
-    ndk::ScopedAStatus revokeChallenge(int32_t cookie, int64_t challenge) override;
+    ndk::ScopedAStatus revokeChallenge(int64_t challenge) override;
 
-    ndk::ScopedAStatus enroll(int32_t cookie, const keymaster::HardwareAuthToken& hat,
+    ndk::ScopedAStatus enroll(const keymaster::HardwareAuthToken& hat,
                               EnrollmentType enrollmentType, const std::vector<Feature>& features,
                               const NativeHandle& previewSurface,
                               std::shared_ptr<common::ICancellationSignal>* return_val) override;
 
     ndk::ScopedAStatus authenticate(
-            int32_t cookie, int64_t keystoreOperationId,
+            int64_t keystoreOperationId,
             std::shared_ptr<common::ICancellationSignal>* returnVal) override;
 
     ndk::ScopedAStatus detectInteraction(
-            int32_t cookie, std::shared_ptr<common::ICancellationSignal>* returnVal) override;
+            std::shared_ptr<common::ICancellationSignal>* returnVal) override;
 
-    ndk::ScopedAStatus enumerateEnrollments(int32_t cookie) override;
+    ndk::ScopedAStatus enumerateEnrollments() override;
 
-    ndk::ScopedAStatus removeEnrollments(int32_t cookie,
-                                         const std::vector<int32_t>& enrollmentIds) override;
+    ndk::ScopedAStatus removeEnrollments(const std::vector<int32_t>& enrollmentIds) override;
 
-    ndk::ScopedAStatus getFeatures(int32_t cookie, int32_t enrollmentId) override;
+    ndk::ScopedAStatus getFeatures(int32_t enrollmentId) override;
 
-    ndk::ScopedAStatus setFeature(int32_t cookie, const keymaster::HardwareAuthToken& hat,
-                                  int32_t enrollmentId, Feature feature, bool enabled) override;
+    ndk::ScopedAStatus setFeature(const keymaster::HardwareAuthToken& hat, int32_t enrollmentId,
+                                  Feature feature, bool enabled) override;
 
-    ndk::ScopedAStatus getAuthenticatorId(int32_t cookie) override;
+    ndk::ScopedAStatus getAuthenticatorId() override;
 
-    ndk::ScopedAStatus invalidateAuthenticatorId(int32_t cookie) override;
+    ndk::ScopedAStatus invalidateAuthenticatorId() override;
 
-    ndk::ScopedAStatus resetLockout(int32_t cookie,
-                                    const keymaster::HardwareAuthToken& hat) override;
+    ndk::ScopedAStatus resetLockout(const keymaster::HardwareAuthToken& hat) override;
 
-    ndk::ScopedAStatus close(int32_t cookie) override;
+    ndk::ScopedAStatus close() override;
 
   private:
     std::shared_ptr<ISessionCallback> cb_;
diff --git a/biometrics/face/aidl/vts/VtsHalBiometricsFaceTargetTest.cpp b/biometrics/face/aidl/vts/VtsHalBiometricsFaceTargetTest.cpp
index 936fcc6..60e0a2a 100644
--- a/biometrics/face/aidl/vts/VtsHalBiometricsFaceTargetTest.cpp
+++ b/biometrics/face/aidl/vts/VtsHalBiometricsFaceTargetTest.cpp
@@ -21,35 +21,31 @@
 #include <android/binder_manager.h>
 #include <android/binder_process.h>
 
+#include <chrono>
 #include <future>
 
 namespace aidl::android::hardware::biometrics::face {
 namespace {
 
+using namespace std::literals::chrono_literals;
+
 constexpr int kSensorId = 0;
 constexpr int kUserId = 0;
-constexpr auto kCallbackTimeout = std::chrono::seconds(1);
 
-enum class SessionCallbackMethodName {
-    kOnStateChanged,
+enum class MethodName {
+    kOnError,
+    kOnSessionClosed,
 };
 
-struct SessionCallbackInvocation {
-    SessionCallbackMethodName method_name;
-    SessionState state;
+struct Invocation {
+    MethodName methodName;
+    Error error;
+    int32_t vendorCode;
 };
 
 class SessionCallback : public BnSessionCallback {
   public:
-    explicit SessionCallback(std::promise<SessionCallbackInvocation> invocation_promise)
-        : invocation_promise_(std::move(invocation_promise)) {}
-    ndk::ScopedAStatus onStateChanged(int32_t /*cookie*/, SessionState state) override {
-        SessionCallbackInvocation invocation = {};
-        invocation.method_name = SessionCallbackMethodName::kOnStateChanged;
-        invocation.state = state;
-        invocation_promise_.set_value(invocation);
-        return ndk::ScopedAStatus::ok();
-    }
+    explicit SessionCallback(Invocation* inv) : mInv(inv) {}
 
     ndk::ScopedAStatus onChallengeGenerated(int64_t /*challenge*/) override {
         return ndk::ScopedAStatus::ok();
@@ -67,7 +63,12 @@
         return ndk::ScopedAStatus::ok();
     }
 
-    ndk::ScopedAStatus onError(Error /*error*/, int32_t /*vendorCode*/) override {
+    ndk::ScopedAStatus onError(Error error, int32_t vendorCode) override {
+        *mInv = {};
+        mInv->methodName = MethodName::kOnError;
+        mInv->error = error;
+        mInv->vendorCode = vendorCode;
+
         return ndk::ScopedAStatus::ok();
     }
 
@@ -120,10 +121,15 @@
         return ndk::ScopedAStatus::ok();
     }
 
-    ndk::ScopedAStatus onSessionClosed() override { return ndk::ScopedAStatus::ok(); }
+    ndk::ScopedAStatus onSessionClosed() override {
+        *mInv = {};
+        mInv->methodName = MethodName::kOnSessionClosed;
+
+        return ndk::ScopedAStatus::ok();
+    }
 
   private:
-    std::promise<SessionCallbackInvocation> invocation_promise_;
+    Invocation* mInv;
 };
 
 class Face : public testing::TestWithParam<std::string> {
@@ -131,28 +137,34 @@
     void SetUp() override {
         AIBinder* binder = AServiceManager_waitForService(GetParam().c_str());
         ASSERT_NE(binder, nullptr);
-        hal_ = IFace::fromBinder(ndk::SpAIBinder(binder));
+        mHal = IFace::fromBinder(ndk::SpAIBinder(binder));
     }
 
-    std::shared_ptr<IFace> hal_;
+    std::shared_ptr<IFace> mHal;
+    Invocation mInv;
 };
 
 TEST_P(Face, AuthenticateTest) {
-    std::promise<SessionCallbackInvocation> invocation_promise;
-    std::future<SessionCallbackInvocation> invocation_future = invocation_promise.get_future();
-    std::shared_ptr<SessionCallback> session_cb =
-            ndk::SharedRefBase::make<SessionCallback>(std::move(invocation_promise));
+    // Prepare the callback.
+    auto cb = ndk::SharedRefBase::make<SessionCallback>(&mInv);
 
+    // Create a session
     std::shared_ptr<ISession> session;
-    ASSERT_TRUE(hal_->createSession(kSensorId, kUserId, session_cb, &session).isOk());
+    ASSERT_TRUE(mHal->createSession(kSensorId, kUserId, cb, &session).isOk());
 
-    std::shared_ptr<common::ICancellationSignal> cancel_cb;
-    ASSERT_TRUE(session->authenticate(0, 0, &cancel_cb).isOk());
-    ASSERT_EQ(invocation_future.wait_for(kCallbackTimeout), std::future_status::ready);
+    // Call authenticate
+    std::shared_ptr<common::ICancellationSignal> cancellationSignal;
+    ASSERT_TRUE(session->authenticate(0 /* operationId */, &cancellationSignal).isOk());
 
-    SessionCallbackInvocation invocation = invocation_future.get();
-    EXPECT_EQ(invocation.method_name, SessionCallbackMethodName::kOnStateChanged);
-    EXPECT_EQ(invocation.state, SessionState::AUTHENTICATING);
+    // Get the results
+    EXPECT_EQ(mInv.methodName, MethodName::kOnError);
+    EXPECT_EQ(mInv.error, Error::UNABLE_TO_PROCESS);
+    EXPECT_EQ(mInv.vendorCode, 0);
+
+    // Close the session
+    ASSERT_TRUE(session->close().isOk());
+
+    EXPECT_EQ(mInv.methodName, MethodName::kOnSessionClosed);
 }
 
 GTEST_ALLOW_UNINSTANTIATED_PARAMETERIZED_TEST(Face);
@@ -161,6 +173,7 @@
                          ::android::PrintInstanceNameToString);
 
 }  // namespace
+}  // namespace aidl::android::hardware::biometrics::face
 
 int main(int argc, char** argv) {
     ::testing::InitGoogleTest(&argc, argv);
@@ -169,4 +182,3 @@
     return RUN_ALL_TESTS();
 }
 
-}  // namespace aidl::android::hardware::biometrics::face
diff --git a/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISession.aidl b/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISession.aidl
index 87eaf96..9934a76 100644
--- a/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISession.aidl
+++ b/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISession.aidl
@@ -34,17 +34,17 @@
 package android.hardware.biometrics.fingerprint;
 @VintfStability
 interface ISession {
-  void generateChallenge(in int cookie);
-  void revokeChallenge(in int cookie, in long challenge);
-  android.hardware.biometrics.common.ICancellationSignal enroll(in int cookie, in android.hardware.keymaster.HardwareAuthToken hat);
-  android.hardware.biometrics.common.ICancellationSignal authenticate(in int cookie, in long operationId);
-  android.hardware.biometrics.common.ICancellationSignal detectInteraction(in int cookie);
-  void enumerateEnrollments(in int cookie);
-  void removeEnrollments(in int cookie, in int[] enrollmentIds);
-  void getAuthenticatorId(in int cookie);
-  void invalidateAuthenticatorId(in int cookie);
-  void resetLockout(in int cookie, in android.hardware.keymaster.HardwareAuthToken hat);
-  void close(in int cookie);
+  void generateChallenge();
+  void revokeChallenge(in long challenge);
+  android.hardware.biometrics.common.ICancellationSignal enroll(in android.hardware.keymaster.HardwareAuthToken hat);
+  android.hardware.biometrics.common.ICancellationSignal authenticate(in long operationId);
+  android.hardware.biometrics.common.ICancellationSignal detectInteraction();
+  void enumerateEnrollments();
+  void removeEnrollments(in int[] enrollmentIds);
+  void getAuthenticatorId();
+  void invalidateAuthenticatorId();
+  void resetLockout(in android.hardware.keymaster.HardwareAuthToken hat);
+  void close();
   void onPointerDown(in int pointerId, in int x, in int y, in float minor, in float major);
   void onPointerUp(in int pointerId);
   void onUiReady();
diff --git a/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISessionCallback.aidl b/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISessionCallback.aidl
index 3a97717..3c40ad6 100644
--- a/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISessionCallback.aidl
+++ b/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/ISessionCallback.aidl
@@ -34,7 +34,6 @@
 package android.hardware.biometrics.fingerprint;
 @VintfStability
 interface ISessionCallback {
-  void onStateChanged(in int cookie, in android.hardware.biometrics.fingerprint.SessionState state);
   void onChallengeGenerated(in long challenge);
   void onChallengeRevoked(in long challenge);
   void onAcquired(in android.hardware.biometrics.fingerprint.AcquiredInfo info, in int vendorCode);
diff --git a/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/SessionState.aidl b/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/SessionState.aidl
deleted file mode 100644
index 9b0b6f6..0000000
--- a/biometrics/fingerprint/aidl/aidl_api/android.hardware.biometrics.fingerprint/current/android/hardware/biometrics/fingerprint/SessionState.aidl
+++ /dev/null
@@ -1,49 +0,0 @@
-/*
- * Copyright (C) 2020 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-///////////////////////////////////////////////////////////////////////////////
-// THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
-///////////////////////////////////////////////////////////////////////////////
-
-// This file is a snapshot of an AIDL file. Do not edit it manually. There are
-// two cases:
-// 1). this is a frozen version file - do not edit this in any case.
-// 2). this is a 'current' file. If you make a backwards compatible change to
-//     the interface (from the latest frozen version), the build system will
-//     prompt you to update this file with `m <name>-update-api`.
-//
-// You must not make a backward incompatible change to any AIDL file built
-// with the aidl_interface module type with versions property set. The module
-// type is used to build AIDL files in a way that they can be used across
-// independently updatable components of the system. If a device is shipped
-// with such a backward incompatible change, it has a high risk of breaking
-// later when a module using the interface is updated, e.g., Mainline modules.
-
-package android.hardware.biometrics.fingerprint;
-@Backing(type="byte") @VintfStability
-enum SessionState {
-  IDLING = 0,
-  CLOSED = 1,
-  GENERATING_CHALLENGE = 2,
-  REVOKING_CHALLENGE = 3,
-  ENROLLING = 4,
-  AUTHENTICATING = 5,
-  DETECTING_INTERACTION = 6,
-  ENUMERATING_ENROLLMENTS = 7,
-  REMOVING_ENROLLMENTS = 8,
-  GETTING_AUTHENTICATOR_ID = 9,
-  INVALIDATING_AUTHENTICATOR_ID = 10,
-  RESETTING_LOCKOUT = 11,
-}
diff --git a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/IFingerprint.aidl b/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/IFingerprint.aidl
index 98a4530..271a9bf 100644
--- a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/IFingerprint.aidl
+++ b/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/IFingerprint.aidl
@@ -32,27 +32,14 @@
     /**
      * createSession:
      *
-     * Creates a session which can then be used by the framework to perform operations such as
-     * enroll, authenticate, etc for the given sensorId and userId.
+     * Creates a instance of ISession which can be used by the framework to perform operations
+     * such as ISession#enroll, ISession#authenticate, etc. for the given sensorId and userId.
      *
-     * Calling this method while there is an active session is considered an error. If the
-     * framework is in a bad state and for some reason cannot close its session, it should use
-     * the reset method below.
-     *
-     * A physical sensor identified by sensorId typically supports only a single in-flight session
-     * at a time. As such, if a session is currently in a state other than SessionState::IDLING, the
-     * HAL MUST finish or cancel the current operation and return to SessionState::IDLING before the
-     * new session is created. For example:
-     *   1) If a session for sensorId=0, userId=0 is currently in a cancellable state (see
-     *      ICancellationSignal) such as SessionState::AUTHENTICATING and the framework requests a
-     *      new session for sensorId=0, userId=10, the HAL must end the current session with
-     *      Error::CANCELED, invoke ISessionCallback#onStateChanged with SessionState::IDLING, and
-     *      then return a new session for sensorId=0, userId=10.
-     *   2) If a session for sensorId=0, userId=0 is currently in a non-cancellable state such as
-     *      SessionState::REMOVING_ENROLLMENTS, and the framework requests a new session for
-     *      sensorId=0, userId=10, the HAL must finish the current operation before invoking
-     *      ISessionCallback#onStateChanged with SessionState::IDLING, and return a new session for
-     *      sensorId=0, userId=10.
+     * Calling this method while there is an active session is considered an error. If the framework
+     * wants to create a new session when it already has an active session, it must first cancel the
+     * current operation if it's cancellable, or wait until it completes. Then, the framework must
+     * explicitly close the session with ISession#close. Once the framework receives
+     * ISessionCallback#onSessionClosed, a new session can be created.
      *
      * Implementations must store user-specific state or metadata in /data/vendor_de/<user>/fpdata
      * as specified by the SeLinux policy. This directory is created/removed by vold (see
diff --git a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISession.aidl b/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISession.aidl
index ef2e6fc..940548b 100644
--- a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISession.aidl
+++ b/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISession.aidl
@@ -22,23 +22,28 @@
 /**
  * Operations that can be performed for unique sessions retrieved via IFingerprint#createSession.
  * Methods defined within this interface can be split into the following categories:
- *   1) Methods associated with a state (see the SessionState enum). State-based operations are
- *      handled by the HAL in FIFO order.
- *   1a) Cancellable state-based operations. If a cancellable operation is in-progress and the
- *       framework requests a subsequent state-based operation, the implementation should finish
- *       the operation via ISessionCallback#onError with Error::CANCELED.
- *   1b) Non-cancellable state-based operations. These operations should fully complete before the
- *       next state-based operation can be started.
- *   2) Methods without a state. These methods may be invoked by the framework depending on its
- *      use case. For example on devices with sensors of FingerprintSensorType::UNDER_DISPLAY_*,
- *      ISession#onFingerDown may be invoked while the HAL is in SessionState::ENROLLING,
- *      SessionState::AUTHENTICATING, or SessionState::DETECTING_INTERACTION.
+ *   1) Non-interrupting operations. These operations are handled by the HAL in FIFO order.
+ *   1a) Cancellable operations. These are usually the operations that can execute for several
+ *       minutes. To allow for cancellation, they return an instance of ICancellationSignal that
+ *       lets the framework cancel them by calling ICancellationSignal#cancel. If such an operation
+ *       is cancelled, it must notify the framework by calling ISessionCallback#onError with
+ *       Error::CANCELED.
+ *   1b) Non-cancellable operations. Such operations cannot be cancelled once started.
+ *   2) Interrupting operations. These operations may be invoked by the framework immediately,
+ *      regardless of whether another operation is executing. For example, on devices with sensors
+ *      of FingerprintSensorType::UNDER_DISPLAY_*, ISession#onFingerDown may be invoked while the
+ *      HAL is executing ISession#enroll, ISession#authenticate or ISession#detectInteraction.
  *
- * If the HAL has multiple operations in its queue, it is not required to notify the framework
- * of SessionState::IDLING between each operation. However, it must notify the framework when all
- * work is completed. See ISessionCallback#onStateChanged. For example, the following is a valid
- * sequence of ISessionCallback#onStateChanged invocations: SessionState::IDLING -->
- * SessionState::ENROLLING --> SessionState::ENUMERATING_ENROLLMENTS --> SessionState::IDLING.
+ * The lifecycle of a non-interrupting operation ends when one of its terminal callbacks is called.
+ * For example, ISession#authenticate is considered completed when either of the following callbacks
+ * is called: ISessionCallback#onError or ISessionCallback#onAuthenticationSucceeded.
+ *
+ * The lifecycle of an interrupting operation ends when it returns. Interrupting operations do not
+ * have callbacks.
+ *
+ * ISession only supports execution of one non-interrupting operation at a time, regardless of
+ * whether it's cancellable. The framework must wait for a corresponding callback indicating the end of
+ * the current non-interrupting operation before a new non-interrupting operation can be started.
  */
 @VintfStability
 interface ISession {
@@ -84,9 +89,8 @@
      * | 0        | 10     | <Time4>    | <Random4> |
      * ----------------------------------------------
      *
-     * @param cookie A unique number identifying this operation
      */
-    void generateChallenge(in int cookie);
+    void generateChallenge();
 
     /**
      * revokeChallenge:
@@ -95,23 +99,17 @@
      * parameters is requested, the implementation must still notify the framework using the
      * provided callback.
      *
-     * @param cookie A unique number identifying this operation
      * @param challenge Challenge that should be revoked.
      */
-    void revokeChallenge(in int cookie, in long challenge);
+    void revokeChallenge(in long challenge);
 
     /**
      * enroll:
      *
      * A request to add a fingerprint enrollment.
      *
-     * Once the HAL is able to start processing the enrollment request, it must notify the framework
-     * via ISessionCallback#onStateChanged with SessionState::ENROLLING.
-     *
      * At any point during enrollment, if a non-recoverable error occurs, the HAL must notify the
-     * framework via ISessionCallback#onError with the applicable enrollment-specific error, and
-     * then send ISessionCallback#onStateChanged(cookie, SessionState::IDLING) if no subsequent
-     * operation is in the queue.
+     * framework via ISessionCallback#onError with the applicable enrollment-specific error.
      *
      * Before capturing fingerprint data, the implementation must first verify the authenticity and
      * integrity of the provided HardwareAuthToken. In addition, it must check that the challenge
@@ -132,24 +130,17 @@
      * implementation MUST update and associate this (sensorId, userId) pair with a new new
      * entropy-encoded random identifier. See ISession#getAuthenticatorId for more information.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param hat See above documentation.
      */
-    ICancellationSignal enroll(in int cookie, in HardwareAuthToken hat);
+    ICancellationSignal enroll(in HardwareAuthToken hat);
 
     /**
      * authenticate:
      *
      * A request to start looking for fingerprints to authenticate.
      *
-     * Once the HAL is able to start processing the authentication request, it must notify framework
-     * via ISessionCallback#onStateChanged with SessionState::AUTHENTICATING.
-     *
      * At any point during authentication, if a non-recoverable error occurs, the HAL must notify
-     * the framework via ISessionCallback#onError with the applicable authentication-specific error,
-     * and then send ISessionCallback#onStateChanged(cookie, SessionState::IDLING) if no
-     * subsequent operation is in the queue.
+     * the framework via ISessionCallback#onError with the applicable authentication-specific error.
      *
      * During authentication, the implementation may notify the framework via
      * ISessionCallback#onAcquired with messages that may be used to guide the user. This callback
@@ -171,8 +162,6 @@
      * must be set with the operationId passed in during #authenticate. If the sensor is NOT
      * SensorStrength::STRONG, the HardwareAuthToken MUST be null.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param operationId For sensors configured as SensorStrength::STRONG, this must be used ONLY
      *                    upon successful authentication and wrapped in the HardwareAuthToken's
      *                    "challenge" field and sent to the framework via
@@ -184,7 +173,7 @@
      *                    setUserAuthenticationParameters in KeyGenParameterSpec.Builder and
      *                    KeyProtection.Builder.
      */
-    ICancellationSignal authenticate(in int cookie, in long operationId);
+    ICancellationSignal authenticate(in long operationId);
 
     /**
      * detectInteraction:
@@ -193,17 +182,12 @@
      * if SensorProps#supportsDetectInteraction is true. If invoked on implementations that do not
      * support this functionality, the HAL must respond with ISession#onError(UNABLE_TO_PROCESS, 0).
      *
-     * Once the HAL is able to start processing this request, it must notify the framework via
-     * ISessionCallback#onStateChanged with SessionState::DETECTING_INTERACTION.
-     *
      * The framework will use this method in cases where determing user presence is required, but
      * identifying/authentication is not. For example, when the device is encrypted (first boot) or
      * in lockdown mode.
      *
      * At any point during detectInteraction, if a non-recoverable error occurs, the HAL must notify
-     * the framework via ISessionCallback#onError with the applicable error, and then send
-     * ISessionCallback#onStateChanged(cookie, SessionState::IDLING) if no subsequent operation is
-     * in the queue.
+     * the framework via ISessionCallback#onError with the applicable error.
      *
      * The implementation must only check for a fingerprint-like image was detected (e.g. to
      * minimize interactions due to non-fingerprint objects), and the lockout counter must not
@@ -221,10 +205,8 @@
      * Note that if the operation is canceled, the implementation must notify the framework via
      * ISessionCallback#onError with Error::CANCELED.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path.
-     *               The framework will guarantee that it is unique per ISession.
      */
-    ICancellationSignal detectInteraction(in int cookie);
+    ICancellationSignal detectInteraction();
 
     /*
      * enumerateEnrollments:
@@ -232,32 +214,22 @@
      * A request to enumerate (list) the enrollments for this (sensorId, userId) pair. The
      * framework typically uses this to ensure that its cache is in sync with the HAL.
      *
-     * Once the HAL is able to start processing this request, it must notify the framework via
-     * ISessionCallback#onStateChanged with SessionState::ENUMERATING_ENROLLMENTS.
-     *
      * The implementation must then notify the framework with a list of enrollments applicable
      * for the current session via ISessionCallback#onEnrollmentsEnumerated.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path.
-     *               The framework will guarantee that it is unique per ISession.
      */
-    void enumerateEnrollments(in int cookie);
+    void enumerateEnrollments();
 
     /**
      * removeEnrollments:
      *
      * A request to remove the enrollments for this (sensorId, userId) pair.
      *
-     * Once the HAL is able to start processing this request, it must notify the framework via
-     * ISessionCallback#onStateChanged with SessionState::REMOVING_ENROLLMENTS.
-     *
      * After removing the enrollmentIds from everywhere necessary (filesystem, secure subsystems,
      * etc), the implementation must notify the framework via ISessionCallback#onEnrollmentsRemoved.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path.
-     *               The framework will guarantee that it is unique per ISession.
      */
-    void removeEnrollments(in int cookie, in int[] enrollmentIds);
+    void removeEnrollments(in int[] enrollmentIds);
 
     /**
      * getAuthenticatorId:
@@ -285,10 +257,8 @@
      *   3) MUST not change if a fingerprint is deleted.
      *   4) MUST be an entropy-encoded random number
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      */
-    void getAuthenticatorId(in int cookie);
+    void getAuthenticatorId();
 
     /**
      * invalidateAuthenticatorId:
@@ -312,10 +282,8 @@
      * for more details). As such, the framework would coordinate invalidation across multiple
      * biometric HALs as necessary.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      */
-    void invalidateAuthenticatorId(in int cookie);
+    void invalidateAuthenticatorId();
 
     /**
      * resetLockout:
@@ -326,8 +294,7 @@
      *   2) Verify that the timestamp provided within the HAT is relatively recent (e.g. on the
      *      order of minutes, not hours).
      * If either of the checks fail, the HAL must invoke ISessionCallback#onError with
-     * Error::UNABLE_TO_PROCESS and return to SessionState::IDLING if no subsequent work is in the
-     * queue.
+     * Error::UNABLE_TO_PROCESS and return to the idling state.
      *
      * Upon successful verification, the HAL must clear the lockout counter and notify the framework
      * via ISessionCallback#onLockoutCleared.
@@ -358,29 +325,26 @@
      * See the Android CDD section 7.3.10 for the full set of lockout and rate-limiting
      * requirements.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      * @param hat HardwareAuthToken See above documentation.
      */
-    void resetLockout(in int cookie, in HardwareAuthToken hat);
+    void resetLockout(in HardwareAuthToken hat);
 
     /*
      * Close this session and allow the HAL to release the resources associated with this session.
      *
-     * A session can only be closed when it's in SessionState::IDLING. Closing a session will
-     * result in a ISessionCallback#onStateChanged call with SessionState::CLOSED.
+     * A session can only be closed when the HAL is idling, i.e. not performing any of the
+     * non-interruptable operations. If the HAL is busy performing a cancellable operation, the
+     * operation must be explicitly cancelled with a call to ICancellationSignal#cancel before
+     * the session can be closed.
      *
-     * If a session is unresponsive or stuck in a state other than SessionState::CLOSED,
-     * IFingerprint#reset could be used as a last resort to terminate the session and recover the
-     * HAL from a bad state.
+     * After a session is closed, the HAL must notify the framework by calling
+     * ISessionCallback#onSessionClosed.
      *
      * All sessions must be explicitly closed. Calling IFingerprint#createSession while there is an
      * active session is considered an error.
      *
-     * @param cookie An identifier used to track subsystem operations related to this call path. The
-     *               client must guarantee that it is unique per ISession.
      */
-    void close(in int cookie);
+    void close();
 
     /**
      * Methods for notifying the under-display fingerprint sensor about external events.
@@ -394,9 +358,8 @@
      * of other types, the HAL must treat this as a no-op and return immediately.
      *
      * For sensors of type FingerprintSensorType::UNDER_DISPLAY_*, this method is used to notify the
-     * HAL of display touches. This method can be invoked when the session is in one of the
-     * following states: SessionState::ENROLLING, SessionState::AUTHENTICATING, or
-     * SessionState::DETECTING_INTERACTION.
+     * HAL of display touches. This method can be invoked when the HAL is performing any one of:
+     * ISession#authenticate, ISession#enroll, ISession#detectInteraction.
      *
      * Note that the framework will only invoke this method if the event occurred on the display on
      * which this sensor is located.
diff --git a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISessionCallback.aidl b/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISessionCallback.aidl
index cf3a271..95657b3 100644
--- a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISessionCallback.aidl
+++ b/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/ISessionCallback.aidl
@@ -18,17 +18,11 @@
 
 import android.hardware.biometrics.fingerprint.AcquiredInfo;
 import android.hardware.biometrics.fingerprint.Error;
-import android.hardware.biometrics.fingerprint.SessionState;
 import android.hardware.keymaster.HardwareAuthToken;
 
 @VintfStability
 interface ISessionCallback {
     /**
-     * Used to notify the framework of session state changes. See ISession for more information.
-     */
-    void onStateChanged(in int cookie, in SessionState state);
-
-    /**
      * Notifies the framework when a challenge is successfully generated.
      */
     void onChallengeGenerated(in long challenge);
@@ -39,10 +33,10 @@
     void onChallengeRevoked(in long challenge);
 
     /**
-     * This method must only be used to notify the framework during the following states:
-     *   1) SessionState::ENROLLING
-     *   2) SessionState::AUTHENTICATING
-     *   3) SessionState::DETECTING_INTERACTION
+     * This method must only be used to notify the framework during the following operations:
+     *   1) ISession#enroll
+     *   2) ISession#authenticate
+     *   3) ISession#detectInteraction
      *
      * These messages may be used to provide user guidance multiple times if necessary per
      * operation.
@@ -56,18 +50,18 @@
     void onAcquired(in AcquiredInfo info, in int vendorCode);
 
     /**
-     * This method must only be used to notify the framework during the following states:
-     *   1) SessionState::ENROLLING
-     *   2) SessionState::AUTHENTICATING
-     *   3) SessionState::DETECTING_INTERACTION
-     *   4) SessionState::INVALIDATING_AUTHENTICATOR_ID
-     *   5) SessionState::RESETTING_LOCKOUT
+     * This method must only be used to notify the framework during the following operations:
+     *   1) ISession#enroll
+     *   2) ISession#authenticate
+     *   3) ISession#detectInteraction
+     *   4) ISession#invalidateAuthenticatorId
+     *   5) ISession#resetLockout
      *
      * These messages may be used to notify the framework or user that a non-recoverable error
-     * has occurred. The operation is finished, and the HAL must proceed with the next operation
-     * or return to SessionState::IDLING if the queue is empty.
+     * has occurred. The operation is finished, and the HAL can proceed with the next operation
+     * or return to the idling state.
      *
-     * Note that cancellation (see common::ICancellationSignal) and preemption most be followed with
+     * Note that cancellation (see common::ICancellationSignal) and preemption must be followed with
      * an Error::CANCELED message.
      *
      * @param error See the Error enum.
@@ -79,8 +73,7 @@
     void onError(in Error error, in int vendorCode);
 
     /**
-     * This method must only be used to notify the framework during the following state:
-     *   1) SessionState::ENROLLING
+     * This method must only be used to notify the framework during the ISession#enroll operation.
      *
      * @param enrollmentId Unique stable identifier for the enrollment that's being added by this
      *                     ISession#enroll invocation.
@@ -89,7 +82,7 @@
     void onEnrollmentProgress(in int enrollmentId, int remaining);
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Used to notify the framework upon successful authentication. Note that the authentication
      * lifecycle ends when either 1) a fingerprint is accepted, or 2) an error occurred. The
@@ -104,7 +97,7 @@
     void onAuthenticationSucceeded(in int enrollmentId, in HardwareAuthToken hat);
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Used to notify the framework upon rejected attempts. Note that the authentication
      * lifecycle ends when either 1) a fingerprint is accepted, or 2) an occurred. The
@@ -113,7 +106,7 @@
     void onAuthenticationFailed();
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Authentication is locked out due to too many unsuccessful attempts. This is a rate-limiting
      * lockout, and authentication can be restarted after a period of time. See
@@ -126,7 +119,7 @@
     void onLockoutTimed(in long durationMillis);
 
     /**
-     * This method must only be used to notify the framework during SessionState::AUTHENTICATING.
+     * This method must only be used to notify the framework during ISession#authenticate.
      *
      * Authentication is disabled until the user unlocks with their device credential
      * (PIN/Pattern/Password). See ISession#resetLockout.
@@ -153,7 +146,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::DETECTING_INTERACTION
+     * ISession#detectInteraction
      *
      * Notifies the framework that user interaction occurred. See ISession#detectInteraction.
      */
@@ -161,7 +154,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::ENUMERATING_ENROLLMENTS.
+     * ISession#enumerateEnrollments.
      *
      * Notifies the framework of the current enrollments. See ISession#enumerateEnrollments.
      *
@@ -171,7 +164,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::REMOVING_ENROLLMENTS.
+     * ISession#removeEnrollments.
      *
      * Notifies the framework that the specified enrollments are removed.
      *
@@ -181,7 +174,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::GETTING_AUTHENTICATOR_ID.
+     * ISession#getAuthenticatorId.
      *
      * Notifies the framework with the authenticatorId corresponding to this session's
      * (userId, sensorId) pair.
@@ -192,7 +185,7 @@
 
     /**
      * This method must only be used to notify the framework during
-     * SessionState::INVALIDATING_AUTHENTICATOR_ID.
+     * ISession#invalidateAuthenticatorId.
      *
      * See ISession#invalidateAuthenticatorId for more information.
      *
diff --git a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/SessionState.aidl b/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/SessionState.aidl
deleted file mode 100644
index 19a6ce3..0000000
--- a/biometrics/fingerprint/aidl/android/hardware/biometrics/fingerprint/SessionState.aidl
+++ /dev/null
@@ -1,81 +0,0 @@
-/*
- * Copyright (C) 2020 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package android.hardware.biometrics.fingerprint;
-
-@VintfStability
-@Backing(type="byte")
-enum SessionState {
-    /**
-     * The HAL is not processing any session requests.
-     */
-    IDLING,
-
-    /**
-     * The session has been closed by the client.
-     */
-    CLOSED,
-
-    /**
-     * The HAL is processing the ISession#generateChallenge request.
-     */
-    GENERATING_CHALLENGE,
-
-    /**
-     * The HAL is processing the ISession#revokeChallenge request.
-     */
-    REVOKING_CHALLENGE,
-
-    /**
-     * The HAL is processing the ISession#enroll request.
-     */
-    ENROLLING,
-
-    /**
-     * The HAL is processing the ISession#authenticate request.
-     */
-    AUTHENTICATING,
-
-    /**
-     * The HAL is processing the ISession#detectInteraction request.
-     */
-    DETECTING_INTERACTION,
-
-    /**
-     * The HAL is processing the ISession#enumerateEnrollments request.
-     */
-    ENUMERATING_ENROLLMENTS,
-
-    /**
-     * The HAL is processing the ISession#removeEnrollments request.
-     */
-    REMOVING_ENROLLMENTS,
-
-    /**
-     * The HAL is processing the ISession#getAuthenticatorId request.
-     */
-    GETTING_AUTHENTICATOR_ID,
-
-    /**
-     * The HAL is processing the ISession#invalidateAuthenticatorId request.
-     */
-    INVALIDATING_AUTHENTICATOR_ID,
-
-    /**
-     * The HAL is processing the ISession#resetLockout request.
-     */
-    RESETTING_LOCKOUT
-}
diff --git a/biometrics/fingerprint/aidl/default/Fingerprint.cpp b/biometrics/fingerprint/aidl/default/Fingerprint.cpp
index fbfa52f..734ff60 100644
--- a/biometrics/fingerprint/aidl/default/Fingerprint.cpp
+++ b/biometrics/fingerprint/aidl/default/Fingerprint.cpp
@@ -22,7 +22,7 @@
 namespace {
 constexpr size_t MAX_WORKER_QUEUE_SIZE = 5;
 constexpr int SENSOR_ID = 1;
-constexpr common::SensorStrength SENSOR_STRENGTH = common::SensorStrength::STRONG;
+constexpr common::SensorStrength SENSOR_STRENGTH = common::SensorStrength::WEAK;
 constexpr int MAX_ENROLLMENTS_PER_USER = 5;
 constexpr FingerprintSensorType SENSOR_TYPE = FingerprintSensorType::REAR;
 constexpr bool SUPPORTS_NAVIGATION_GESTURES = true;
diff --git a/biometrics/fingerprint/aidl/default/Session.cpp b/biometrics/fingerprint/aidl/default/Session.cpp
index f030f13..ca481e7 100644
--- a/biometrics/fingerprint/aidl/default/Session.cpp
+++ b/biometrics/fingerprint/aidl/default/Session.cpp
@@ -39,54 +39,56 @@
 }
 
 void Session::scheduleStateOrCrash(SessionState state) {
-    CHECK(mScheduledState == SessionState::IDLING);
-    CHECK(mCurrentState == SessionState::IDLING);
+    // TODO(b/166800618): call enterIdling from the terminal callbacks and restore these checks.
+    // CHECK(mScheduledState == SessionState::IDLING);
+    // CHECK(mCurrentState == SessionState::IDLING);
     mScheduledState = state;
 }
 
-void Session::enterStateOrCrash(int cookie, SessionState state) {
+void Session::enterStateOrCrash(SessionState state) {
     CHECK(mScheduledState == state);
     mCurrentState = state;
     mScheduledState = SessionState::IDLING;
-    mCb->onStateChanged(cookie, mCurrentState);
 }
 
-void Session::enterIdling(int cookie) {
-    mCurrentState = SessionState::IDLING;
-    mCb->onStateChanged(cookie, mCurrentState);
+void Session::enterIdling() {
+    // TODO(b/166800618): call enterIdling from the terminal callbacks and rethink this conditional.
+    if (mCurrentState != SessionState::CLOSED) {
+        mCurrentState = SessionState::IDLING;
+    }
 }
 
 bool Session::isClosed() {
     return mCurrentState == SessionState::CLOSED;
 }
 
-ndk::ScopedAStatus Session::generateChallenge(int32_t cookie) {
+ndk::ScopedAStatus Session::generateChallenge() {
     LOG(INFO) << "generateChallenge";
     scheduleStateOrCrash(SessionState::GENERATING_CHALLENGE);
 
-    mWorker->schedule(Callable::from([this, cookie] {
-        enterStateOrCrash(cookie, SessionState::GENERATING_CHALLENGE);
+    mWorker->schedule(Callable::from([this] {
+        enterStateOrCrash(SessionState::GENERATING_CHALLENGE);
         mEngine->generateChallengeImpl(mCb.get());
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::revokeChallenge(int32_t cookie, int64_t challenge) {
+ndk::ScopedAStatus Session::revokeChallenge(int64_t challenge) {
     LOG(INFO) << "revokeChallenge";
     scheduleStateOrCrash(SessionState::REVOKING_CHALLENGE);
 
-    mWorker->schedule(Callable::from([this, cookie, challenge] {
-        enterStateOrCrash(cookie, SessionState::REVOKING_CHALLENGE);
+    mWorker->schedule(Callable::from([this, challenge] {
+        enterStateOrCrash(SessionState::REVOKING_CHALLENGE);
         mEngine->revokeChallengeImpl(mCb.get(), challenge);
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::enroll(int32_t cookie, const keymaster::HardwareAuthToken& hat,
+ndk::ScopedAStatus Session::enroll(const keymaster::HardwareAuthToken& hat,
                                    std::shared_ptr<common::ICancellationSignal>* out) {
     LOG(INFO) << "enroll";
     scheduleStateOrCrash(SessionState::ENROLLING);
@@ -94,21 +96,21 @@
     std::promise<void> cancellationPromise;
     auto cancFuture = cancellationPromise.get_future();
 
-    mWorker->schedule(Callable::from([this, cookie, hat, cancFuture = std::move(cancFuture)] {
-        enterStateOrCrash(cookie, SessionState::ENROLLING);
+    mWorker->schedule(Callable::from([this, hat, cancFuture = std::move(cancFuture)] {
+        enterStateOrCrash(SessionState::ENROLLING);
         if (shouldCancel(cancFuture)) {
             mCb->onError(Error::CANCELED, 0 /* vendorCode */);
         } else {
             mEngine->enrollImpl(mCb.get(), hat);
         }
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     *out = SharedRefBase::make<CancellationSignal>(std::move(cancellationPromise));
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::authenticate(int32_t cookie, int64_t operationId,
+ndk::ScopedAStatus Session::authenticate(int64_t operationId,
                                          std::shared_ptr<common::ICancellationSignal>* out) {
     LOG(INFO) << "authenticate";
     scheduleStateOrCrash(SessionState::AUTHENTICATING);
@@ -116,112 +118,111 @@
     std::promise<void> cancPromise;
     auto cancFuture = cancPromise.get_future();
 
-    mWorker->schedule(
-            Callable::from([this, cookie, operationId, cancFuture = std::move(cancFuture)] {
-                enterStateOrCrash(cookie, SessionState::AUTHENTICATING);
-                if (shouldCancel(cancFuture)) {
-                    mCb->onError(Error::CANCELED, 0 /* vendorCode */);
-                } else {
-                    mEngine->authenticateImpl(mCb.get(), operationId);
-                }
-                enterIdling(cookie);
-            }));
+    mWorker->schedule(Callable::from([this, operationId, cancFuture = std::move(cancFuture)] {
+        enterStateOrCrash(SessionState::AUTHENTICATING);
+        if (shouldCancel(cancFuture)) {
+            mCb->onError(Error::CANCELED, 0 /* vendorCode */);
+        } else {
+            mEngine->authenticateImpl(mCb.get(), operationId);
+        }
+        enterIdling();
+    }));
 
     *out = SharedRefBase::make<CancellationSignal>(std::move(cancPromise));
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::detectInteraction(int32_t cookie,
-                                              std::shared_ptr<common::ICancellationSignal>* out) {
+ndk::ScopedAStatus Session::detectInteraction(std::shared_ptr<common::ICancellationSignal>* out) {
     LOG(INFO) << "detectInteraction";
     scheduleStateOrCrash(SessionState::DETECTING_INTERACTION);
 
     std::promise<void> cancellationPromise;
     auto cancFuture = cancellationPromise.get_future();
 
-    mWorker->schedule(Callable::from([this, cookie, cancFuture = std::move(cancFuture)] {
-        enterStateOrCrash(cookie, SessionState::DETECTING_INTERACTION);
+    mWorker->schedule(Callable::from([this, cancFuture = std::move(cancFuture)] {
+        enterStateOrCrash(SessionState::DETECTING_INTERACTION);
         if (shouldCancel(cancFuture)) {
             mCb->onError(Error::CANCELED, 0 /* vendorCode */);
         } else {
             mEngine->detectInteractionImpl(mCb.get());
         }
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     *out = SharedRefBase::make<CancellationSignal>(std::move(cancellationPromise));
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::enumerateEnrollments(int32_t cookie) {
+ndk::ScopedAStatus Session::enumerateEnrollments() {
     LOG(INFO) << "enumerateEnrollments";
     scheduleStateOrCrash(SessionState::ENUMERATING_ENROLLMENTS);
 
-    mWorker->schedule(Callable::from([this, cookie] {
-        enterStateOrCrash(cookie, SessionState::ENUMERATING_ENROLLMENTS);
+    mWorker->schedule(Callable::from([this] {
+        enterStateOrCrash(SessionState::ENUMERATING_ENROLLMENTS);
         mEngine->enumerateEnrollmentsImpl(mCb.get());
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::removeEnrollments(int32_t cookie,
-                                              const std::vector<int32_t>& enrollmentIds) {
+ndk::ScopedAStatus Session::removeEnrollments(const std::vector<int32_t>& enrollmentIds) {
     LOG(INFO) << "removeEnrollments";
     scheduleStateOrCrash(SessionState::REMOVING_ENROLLMENTS);
 
-    mWorker->schedule(Callable::from([this, cookie, enrollmentIds] {
-        enterStateOrCrash(cookie, SessionState::REMOVING_ENROLLMENTS);
+    mWorker->schedule(Callable::from([this, enrollmentIds] {
+        enterStateOrCrash(SessionState::REMOVING_ENROLLMENTS);
         mEngine->removeEnrollmentsImpl(mCb.get(), enrollmentIds);
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::getAuthenticatorId(int32_t cookie) {
+ndk::ScopedAStatus Session::getAuthenticatorId() {
     LOG(INFO) << "getAuthenticatorId";
     scheduleStateOrCrash(SessionState::GETTING_AUTHENTICATOR_ID);
 
-    mWorker->schedule(Callable::from([this, cookie] {
-        enterStateOrCrash(cookie, SessionState::GETTING_AUTHENTICATOR_ID);
+    mWorker->schedule(Callable::from([this] {
+        enterStateOrCrash(SessionState::GETTING_AUTHENTICATOR_ID);
         mEngine->getAuthenticatorIdImpl(mCb.get());
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::invalidateAuthenticatorId(int32_t cookie) {
+ndk::ScopedAStatus Session::invalidateAuthenticatorId() {
     LOG(INFO) << "invalidateAuthenticatorId";
     scheduleStateOrCrash(SessionState::INVALIDATING_AUTHENTICATOR_ID);
 
-    mWorker->schedule(Callable::from([this, cookie] {
-        enterStateOrCrash(cookie, SessionState::INVALIDATING_AUTHENTICATOR_ID);
+    mWorker->schedule(Callable::from([this] {
+        enterStateOrCrash(SessionState::INVALIDATING_AUTHENTICATOR_ID);
         mEngine->invalidateAuthenticatorIdImpl(mCb.get());
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::resetLockout(int32_t cookie, const keymaster::HardwareAuthToken& hat) {
+ndk::ScopedAStatus Session::resetLockout(const keymaster::HardwareAuthToken& hat) {
     LOG(INFO) << "resetLockout";
     scheduleStateOrCrash(SessionState::RESETTING_LOCKOUT);
 
-    mWorker->schedule(Callable::from([this, cookie, hat] {
-        enterStateOrCrash(cookie, SessionState::RESETTING_LOCKOUT);
+    mWorker->schedule(Callable::from([this, hat] {
+        enterStateOrCrash(SessionState::RESETTING_LOCKOUT);
         mEngine->resetLockoutImpl(mCb.get(), hat);
-        enterIdling(cookie);
+        enterIdling();
     }));
 
     return ndk::ScopedAStatus::ok();
 }
 
-ndk::ScopedAStatus Session::close(int32_t /*cookie*/) {
+ndk::ScopedAStatus Session::close() {
     LOG(INFO) << "close";
-    CHECK(mCurrentState == SessionState::IDLING) << "Can't close a non-idling session. Crashing.";
+    // TODO(b/166800618): call enterIdling from the terminal callbacks and restore this check.
+    // CHECK(mCurrentState == SessionState::IDLING) << "Can't close a non-idling session.
+    // Crashing.";
     mCurrentState = SessionState::CLOSED;
     mCb->onSessionClosed();
     return ndk::ScopedAStatus::ok();
diff --git a/biometrics/fingerprint/aidl/default/include/FakeFingerprintEngine.h b/biometrics/fingerprint/aidl/default/include/FakeFingerprintEngine.h
index 42e1aa5..6667f7a 100644
--- a/biometrics/fingerprint/aidl/default/include/FakeFingerprintEngine.h
+++ b/biometrics/fingerprint/aidl/default/include/FakeFingerprintEngine.h
@@ -37,7 +37,7 @@
         cb->onEnrollmentProgress(0 /* enrollmentId */, 0 /* remaining */);
     }
 
-    void authenticateImpl(ISessionCallback* cb, int64_t /*operationId*/) {
+    void authenticateImpl(ISessionCallback* cb, int64_t /* operationId */) {
         LOG(INFO) << "authenticateImpl";
         cb->onAuthenticationSucceeded(0 /* enrollmentId */, {} /* hat */);
     }
diff --git a/biometrics/fingerprint/aidl/default/include/Session.h b/biometrics/fingerprint/aidl/default/include/Session.h
index 97d5645..9e46422 100644
--- a/biometrics/fingerprint/aidl/default/include/Session.h
+++ b/biometrics/fingerprint/aidl/default/include/Session.h
@@ -27,37 +27,50 @@
 namespace common = aidl::android::hardware::biometrics::common;
 namespace keymaster = aidl::android::hardware::keymaster;
 
+enum class SessionState {
+    IDLING,
+    CLOSED,
+    GENERATING_CHALLENGE,
+    REVOKING_CHALLENGE,
+    ENROLLING,
+    AUTHENTICATING,
+    DETECTING_INTERACTION,
+    ENUMERATING_ENROLLMENTS,
+    REMOVING_ENROLLMENTS,
+    GETTING_AUTHENTICATOR_ID,
+    INVALIDATING_AUTHENTICATOR_ID,
+    RESETTING_LOCKOUT,
+};
+
 class Session : public BnSession {
   public:
     Session(int sensorId, int userId, std::shared_ptr<ISessionCallback> cb,
             FakeFingerprintEngine* engine, WorkerThread* worker);
 
-    ndk::ScopedAStatus generateChallenge(int32_t cookie) override;
+    ndk::ScopedAStatus generateChallenge() override;
 
-    ndk::ScopedAStatus revokeChallenge(int32_t cookie, int64_t challenge) override;
+    ndk::ScopedAStatus revokeChallenge(int64_t challenge) override;
 
-    ndk::ScopedAStatus enroll(int32_t cookie, const keymaster::HardwareAuthToken& hat,
+    ndk::ScopedAStatus enroll(const keymaster::HardwareAuthToken& hat,
                               std::shared_ptr<common::ICancellationSignal>* out) override;
 
-    ndk::ScopedAStatus authenticate(int32_t cookie, int64_t operationId,
+    ndk::ScopedAStatus authenticate(int64_t operationId,
                                     std::shared_ptr<common::ICancellationSignal>* out) override;
 
     ndk::ScopedAStatus detectInteraction(
-            int32_t cookie, std::shared_ptr<common::ICancellationSignal>* out) override;
+            std::shared_ptr<common::ICancellationSignal>* out) override;
 
-    ndk::ScopedAStatus enumerateEnrollments(int32_t cookie) override;
+    ndk::ScopedAStatus enumerateEnrollments() override;
 
-    ndk::ScopedAStatus removeEnrollments(int32_t cookie,
-                                         const std::vector<int32_t>& enrollmentIds) override;
+    ndk::ScopedAStatus removeEnrollments(const std::vector<int32_t>& enrollmentIds) override;
 
-    ndk::ScopedAStatus getAuthenticatorId(int32_t cookie) override;
+    ndk::ScopedAStatus getAuthenticatorId() override;
 
-    ndk::ScopedAStatus invalidateAuthenticatorId(int32_t cookie) override;
+    ndk::ScopedAStatus invalidateAuthenticatorId() override;
 
-    ndk::ScopedAStatus resetLockout(int32_t cookie,
-                                    const keymaster::HardwareAuthToken& hat) override;
+    ndk::ScopedAStatus resetLockout(const keymaster::HardwareAuthToken& hat) override;
 
-    ndk::ScopedAStatus close(int32_t cookie) override;
+    ndk::ScopedAStatus close() override;
 
     ndk::ScopedAStatus onPointerDown(int32_t pointerId, int32_t x, int32_t y, float minor,
                                      float major) override;
@@ -76,11 +89,11 @@
     // Crashes the HAL if the provided state doesn't match the previously scheduled state.
     // Otherwise, transitions into the provided state, clears the scheduled state, and notifies
     // the client about the transition by calling ISessionCallback#onStateChanged.
-    void enterStateOrCrash(int cookie, SessionState state);
+    void enterStateOrCrash(SessionState state);
 
     // Sets the current state to SessionState::IDLING and notifies the client about the transition
     // by calling ISessionCallback#onStateChanged.
-    void enterIdling(int cookie);
+    void enterIdling();
 
     // The sensor and user IDs for which this session was created.
     int32_t mSensorId;
diff --git a/biometrics/fingerprint/aidl/vts/VtsHalBiometricsFingerprintTargetTest.cpp b/biometrics/fingerprint/aidl/vts/VtsHalBiometricsFingerprintTargetTest.cpp
index 885f703..f1cfb17 100644
--- a/biometrics/fingerprint/aidl/vts/VtsHalBiometricsFingerprintTargetTest.cpp
+++ b/biometrics/fingerprint/aidl/vts/VtsHalBiometricsFingerprintTargetTest.cpp
@@ -22,46 +22,20 @@
 #include <android/binder_manager.h>
 #include <android/binder_process.h>
 
+#include <chrono>
 #include <future>
 
 namespace aidl::android::hardware::biometrics::fingerprint {
 namespace {
 
+using namespace std::literals::chrono_literals;
+
 constexpr int kSensorId = 0;
 constexpr int kUserId = 0;
-constexpr auto kCallbackTimeout = std::chrono::seconds(1);
-
-enum class MethodName {
-    kOnStateChanged,
-};
-
-struct Invocation {
-    MethodName methodName;
-    int32_t cookie;
-    SessionState state;
-};
 
 class SessionCallback : public BnSessionCallback {
   public:
-    explicit SessionCallback() : mIsPromiseValid(false) {}
-
-    void setPromise(std::promise<std::vector<Invocation>>&& promise) {
-        mPromise = std::move(promise);
-        mIsPromiseValid = true;
-    }
-
-    ndk::ScopedAStatus onStateChanged(int32_t cookie, SessionState state) override {
-        Invocation invocation = {};
-        invocation.methodName = MethodName::kOnStateChanged;
-        invocation.cookie = cookie;
-        invocation.state = state;
-        mInvocations.push_back(invocation);
-        if (state == SessionState::IDLING) {
-            assert(mIsPromiseValid);
-            mPromise.set_value(mInvocations);
-        }
-        return ndk::ScopedAStatus::ok();
-    }
+    explicit SessionCallback(std::promise<void>&& promise) : mPromise(std::move(promise)) {}
 
     ndk::ScopedAStatus onChallengeGenerated(int64_t /*challenge*/) override {
         return ndk::ScopedAStatus::ok();
@@ -119,12 +93,13 @@
         return ndk::ScopedAStatus::ok();
     }
 
-    ndk::ScopedAStatus onSessionClosed() override { return ndk::ScopedAStatus::ok(); }
+    ndk::ScopedAStatus onSessionClosed() override {
+        mPromise.set_value();
+        return ndk::ScopedAStatus::ok();
+    }
 
   private:
-    bool mIsPromiseValid;
-    std::vector<Invocation> mInvocations;
-    std::promise<std::vector<Invocation>> mPromise;
+    std::promise<void> mPromise;
 };
 
 class Fingerprint : public testing::TestWithParam<std::string> {
@@ -139,33 +114,26 @@
 };
 
 TEST_P(Fingerprint, AuthenticateTest) {
-    // Prepare the callback
-    std::promise<std::vector<Invocation>> promise;
+    auto promise = std::promise<void>{};
     auto future = promise.get_future();
-    std::shared_ptr<SessionCallback> cb = ndk::SharedRefBase::make<SessionCallback>();
-    cb->setPromise(std::move(promise));
+    // Prepare the callback.
+    auto cb = ndk::SharedRefBase::make<SessionCallback>(std::move(promise));
 
     // Create a session
     std::shared_ptr<ISession> session;
     ASSERT_TRUE(mHal->createSession(kSensorId, kUserId, cb, &session).isOk());
 
     // Call authenticate
-    int32_t cookie = 123;
     std::shared_ptr<common::ICancellationSignal> cancellationSignal;
-    ASSERT_TRUE(session->authenticate(cookie, 0, &cancellationSignal).isOk());
+    ASSERT_TRUE(session->authenticate(-1 /* operationId */, &cancellationSignal).isOk());
 
     // Get the results
-    ASSERT_TRUE(future.wait_for(kCallbackTimeout) == std::future_status::ready);
-    std::vector<Invocation> invocations = future.get();
+    // TODO(b/166799066): test authenticate.
 
     // Close the session
-    ASSERT_TRUE(session->close(0).isOk());
-
-    ASSERT_FALSE(invocations.empty());
-    EXPECT_EQ(invocations.front().methodName, MethodName::kOnStateChanged);
-    EXPECT_EQ(invocations.front().state, SessionState::AUTHENTICATING);
-    EXPECT_EQ(invocations.back().methodName, MethodName::kOnStateChanged);
-    EXPECT_EQ(invocations.back().state, SessionState::IDLING);
+    ASSERT_TRUE(session->close().isOk());
+    auto status = future.wait_for(1s);
+    ASSERT_EQ(status, std::future_status::ready);
 }
 
 GTEST_ALLOW_UNINSTANTIATED_PARAMETERIZED_TEST(Fingerprint);