diff --git a/app/Actions/Projects/BuildProjectBacklogPayload.php b/app/Actions/Projects/BuildProjectBacklogPayload.php
index eb71b01..bff6315 100644
--- a/app/Actions/Projects/BuildProjectBacklogPayload.php
+++ b/app/Actions/Projects/BuildProjectBacklogPayload.php
@@ -59,6 +59,7 @@ class BuildProjectBacklogPayload
             )->resolve(),
             'users' => UserResource::collection(
                 User::query()
+                    ->visibleToProject($project)
                     ->orderBy('name')
                     ->get(),
             )->resolve(),
diff --git a/app/Actions/Projects/BuildProjectTicketDetailPayload.php b/app/Actions/Projects/BuildProjectTicketDetailPayload.php
index 26b4511..25257cb 100644
--- a/app/Actions/Projects/BuildProjectTicketDetailPayload.php
+++ b/app/Actions/Projects/BuildProjectTicketDetailPayload.php
@@ -116,6 +116,7 @@ class BuildProjectTicketDetailPayload
             'ticketTypes' => TicketTypeResource::collection($project->ticketTypes()->get())->resolve(),
             'users' => UserResource::collection(
                 User::query()
+                    ->visibleToProject($project)
                     ->orderBy('name')
                     ->get(),
             )->resolve(),
diff --git a/app/Actions/Projects/BuildProjectTicketOptionsPayload.php b/app/Actions/Projects/BuildProjectTicketOptionsPayload.php
index a22aea1..7c6a307 100644
--- a/app/Actions/Projects/BuildProjectTicketOptionsPayload.php
+++ b/app/Actions/Projects/BuildProjectTicketOptionsPayload.php
@@ -38,6 +38,7 @@ class BuildProjectTicketOptionsPayload
             'ticketTypes' => TicketTypeResource::collection($project->ticketTypes()->get())->resolve(),
             'users' => UserResource::collection(
                 User::query()
+                    ->visibleToProject($project)
                     ->orderBy('name')
                     ->get(),
             )->resolve(),
diff --git a/app/Http/Controllers/Api/ProjectTicketController.php b/app/Http/Controllers/Api/ProjectTicketController.php
index 02409e5..337fda9 100644
--- a/app/Http/Controllers/Api/ProjectTicketController.php
+++ b/app/Http/Controllers/Api/ProjectTicketController.php
@@ -123,7 +123,8 @@ class ProjectTicketController extends ApiController
             ? "{$ticket->ticket_key} was updated."
             : 'No ticket changes were detected.';
 
-        return TicketResource::make($ticket->fresh()->load([
+        $canManageProject = $this->permissionService->allows($user, Permission::ProjectAdmin, $project);
+        $displayTicket = $ticket->fresh([
             'assignee',
             'author',
             'fieldValues.ticketFieldDefinition',
@@ -132,7 +133,23 @@ class ProjectTicketController extends ApiController
             'ticketStatus.boardColumn',
             'ticketType',
             'worklogEntries.actor',
-        ]))
+        ]) ?? $ticket->load([
+            'assignee',
+            'author',
+            'fieldValues.ticketFieldDefinition',
+            'fieldValues.userValue',
+            'ticketPriority',
+            'ticketStatus.boardColumn',
+            'ticketType',
+            'worklogEntries.actor',
+        ]);
+
+        if (! $project->show_author && ! $canManageProject) {
+            $displayTicket->setRelation('author', null);
+            $displayTicket->author_user_id = null;
+        }
+
+        return TicketResource::make($displayTicket)
             ->additional([
                 'meta' => [
                     'message' => $statusMessage,
diff --git a/app/Http/Controllers/Api/UserAssignedTicketController.php b/app/Http/Controllers/Api/UserAssignedTicketController.php
index c750955..cbd01cb 100644
--- a/app/Http/Controllers/Api/UserAssignedTicketController.php
+++ b/app/Http/Controllers/Api/UserAssignedTicketController.php
@@ -18,10 +18,14 @@ class UserAssignedTicketController extends ApiController
     {
         $viewer = $this->authenticatedUser($request);
 
+        $assignedTickets = $this->listAssignedTicketsByVisibleProject->handle($viewer, $user);
+
         return response()->json([
-            'data' => $this->listAssignedTicketsByVisibleProject->handle($viewer, $user),
+            'data' => $assignedTickets,
             'meta' => [
-                'assignee' => UserResource::make($user)->resolve(),
+                'assignee' => $assignedTickets === []
+                    ? null
+                    : UserResource::make($user)->resolve(),
             ],
         ]);
     }
diff --git a/app/Models/User.php b/app/Models/User.php
index a1cc99d..b3dc0ba 100644
--- a/app/Models/User.php
+++ b/app/Models/User.php
@@ -3,9 +3,12 @@
 namespace App\Models;
 
 // use Illuminate\Contracts\Auth\MustVerifyEmail;
+use App\Actions\Permissions\PermissionService;
+use App\Enums\Permission;
 use Database\Factories\UserFactory;
 use Illuminate\Database\Eloquent\Attributes\Fillable;
 use Illuminate\Database\Eloquent\Attributes\Hidden;
+use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Database\Eloquent\Relations\HasMany;
@@ -76,4 +79,22 @@ class User extends Authenticatable
     {
         return $this->hasMany(Ticket::class, 'author_user_id');
     }
+
+    public function scopeVisibleToProject(Builder $query, Project $project): Builder
+    {
+        $permissionService = app(PermissionService::class);
+
+        $allowedUserIds = User::query()
+            ->select('id')
+            ->cursor()
+            ->filter(fn (User $candidate) => $permissionService->allows(
+                $candidate,
+                Permission::ProjectRead,
+                $project
+            ))
+            ->pluck('id')
+            ->all();
+
+        return $query->whereKey($allowedUserIds);
+    }
 }
diff --git a/docs/openapi/kanbangit-api.openapi.json b/docs/openapi/kanbangit-api.openapi.json
index 9a1a607..043b565 100644
--- a/docs/openapi/kanbangit-api.openapi.json
+++ b/docs/openapi/kanbangit-api.openapi.json
@@ -1643,7 +1643,7 @@
         }
       },
       "AssignedTicketsPayload": {
-        "description": "Tickets assigned to a user grouped by projects visible to the authenticated application key owner.",
+        "description": "Tickets assigned to a user grouped by projects visible to the authenticated application key owner. meta.assignee is null when no visible assigned tickets exist.",
         "content": {
           "application/json": {
             "schema": {
@@ -1844,7 +1844,14 @@
             "type": "object",
             "properties": {
               "assignee": {
-                "$ref": "#/components/schemas/User"
+                "anyOf": [
+                  {
+                    "$ref": "#/components/schemas/User"
+                  },
+                  {
+                    "type": "null"
+                  }
+                ]
               }
             },
             "required": ["assignee"]
diff --git a/tests/Feature/Api/AssignedTicketsApiTest.php b/tests/Feature/Api/AssignedTicketsApiTest.php
index 196f39e..0b7647f 100644
--- a/tests/Feature/Api/AssignedTicketsApiTest.php
+++ b/tests/Feature/Api/AssignedTicketsApiTest.php
@@ -77,4 +77,37 @@ class AssignedTicketsApiTest extends TestCase
             ->assertJsonCount(1, 'data.1.tickets')
             ->assertJsonCount(2, 'data');
     }
+
+    public function test_assignee_metadata_is_hidden_when_no_visible_assigned_tickets_exist(): void
+    {
+        $viewer = User::factory()->create();
+        $assignee = User::factory()->create([
+            'name' => 'Hidden User',
+        ]);
+
+        $visibleProject = Project::factory()->create([
+            'key' => 'VIS',
+            'name' => 'Visible project',
+        ]);
+        $hiddenProject = Project::factory()->create([
+            'key' => 'HID',
+            'name' => 'Hidden project',
+        ]);
+
+        $this->syncProjectPermissions($visibleProject, $viewer, ['view']);
+
+        Ticket::factory()->create([
+            'assignee_user_id' => $assignee->id,
+            'project_id' => $hiddenProject->id,
+            'sequence_number' => 1,
+            'ticket_key' => 'HID-1',
+            'title' => 'Hidden ticket',
+        ]);
+
+        $this->withApplicationKey($viewer)
+            ->getJson(route('api.users.assigned-tickets', $assignee))
+            ->assertOk()
+            ->assertJsonPath('data', [])
+            ->assertJsonPath('meta.assignee', null);
+    }
 }
diff --git a/tests/Feature/Api/OpenApiDocumentationTest.php b/tests/Feature/Api/OpenApiDocumentationTest.php
index db2ae00..24418f2 100644
--- a/tests/Feature/Api/OpenApiDocumentationTest.php
+++ b/tests/Feature/Api/OpenApiDocumentationTest.php
@@ -83,5 +83,13 @@ class OpenApiDocumentationTest extends TestCase
         $this->assertArrayHasKey('UserGitConnectionRequest', $document['components']['schemas']);
         $this->assertArrayHasKey('AssignedTicketsPayloadEnvelope', $document['components']['schemas']);
         $this->assertArrayHasKey('AssignedTicketsProjectGroup', $document['components']['schemas']);
+
+        $assigneeSchema = $document['components']['schemas']['AssignedTicketsPayloadEnvelope']['properties']['meta']['properties']['assignee'] ?? null;
+
+        $this->assertIsArray($assigneeSchema);
+        $this->assertSame([
+            ['$ref' => '#/components/schemas/User'],
+            ['type' => 'null'],
+        ], $assigneeSchema['anyOf'] ?? null);
     }
 }
diff --git a/tests/Feature/Api/SettingsApiTest.php b/tests/Feature/Api/SettingsApiTest.php
index 110e656..9747a66 100644
--- a/tests/Feature/Api/SettingsApiTest.php
+++ b/tests/Feature/Api/SettingsApiTest.php
@@ -4,6 +4,7 @@ namespace Tests\Feature\Api;
 
 use App\Actions\ProjectTicketMetadata\InitializeProjectTicketMetadata;
 use App\Models\Project;
+use App\Models\Team;
 use App\Models\User;
 use Illuminate\Foundation\Testing\RefreshDatabase;
 use Illuminate\Support\Facades\Http;
@@ -149,6 +150,45 @@ class SettingsApiTest extends TestCase
             ->assertNoContent();
     }
 
+    public function test_project_payloads_only_return_users_who_can_view_the_project(): void
+    {
+        [$user, $project] = $this->projectContext();
+        $viewer = User::factory()->create(['name' => 'Visible User']);
+        User::factory()->create(['name' => 'Hidden User']);
+        $teamViewer = User::factory()->create(['name' => 'Team Viewer']);
+        $team = Team::factory()->create();
+
+        $this->syncProjectPermissions($project, $viewer, ['view']);
+        $team->users()->attach($teamViewer);
+        $this->syncProjectPermissions($project, $team, ['view']);
+
+        $ticket = $project->tickets()->firstOrCreate([
+            'sequence_number' => 1,
+        ], [
+            'ticket_key' => 'CORE-1',
+            'ticket_priority_id' => $project->ticketPriorities()->firstOrFail()->id,
+            'ticket_status_id' => $project->ticketStatuses()->firstOrFail()->id,
+            'ticket_type_id' => $project->ticketTypes()->where('is_parent', false)->firstOrFail()->id,
+            'title' => 'Scoped users ticket',
+        ]);
+
+        $this->withApplicationKey($user)
+            ->getJson(route('api.projects.backlog', $project))
+            ->assertOk()
+            ->assertJsonPath('data.users.0.name', $user->name)
+            ->assertJsonPath('data.users.1.name', 'Team Viewer')
+            ->assertJsonPath('data.users.2.name', 'Visible User')
+            ->assertJsonCount(3, 'data.users');
+
+        $this->withApplicationKey($user)
+            ->getJson(route('api.projects.tickets.show', [$project, $ticket]))
+            ->assertOk()
+            ->assertJsonPath('data.users.0.name', $user->name)
+            ->assertJsonPath('data.users.1.name', 'Team Viewer')
+            ->assertJsonPath('data.users.2.name', 'Visible User')
+            ->assertJsonCount(3, 'data.users');
+    }
+
     public function test_project_repositories_and_user_git_connections_are_available(): void
     {
         Http::preventStrayRequests();
diff --git a/tests/Feature/Api/TicketApiTest.php b/tests/Feature/Api/TicketApiTest.php
index 5185153..224eadd 100644
--- a/tests/Feature/Api/TicketApiTest.php
+++ b/tests/Feature/Api/TicketApiTest.php
@@ -81,6 +81,77 @@ class TicketApiTest extends TestCase
             ->assertJsonPath('data.ticket.story_points', 5);
     }
 
+    public function test_ticket_update_hides_author_for_non_admins_when_author_visibility_is_disabled(): void
+    {
+        $writer = User::factory()->create();
+        $author = User::factory()->create([
+            'name' => 'Author User',
+        ]);
+        $project = Project::factory()->create([
+            'key' => 'CORE',
+            'show_author' => false,
+        ]);
+
+        app(InitializeProjectTicketMetadata::class)->handle($project);
+
+        $priority = $project->ticketPriorities()->firstOrFail();
+        $status = $project->ticketStatuses()->firstOrFail();
+        $type = $project->ticketTypes()->where('is_parent', false)->firstOrFail();
+
+        $ticket = Ticket::factory()->create([
+            'author_user_id' => $author->id,
+            'project_id' => $project->id,
+            'sequence_number' => 1,
+            'ticket_key' => 'CORE-1',
+            'ticket_priority_id' => $priority->id,
+            'ticket_status_id' => $status->id,
+            'ticket_type_id' => $type->id,
+            'title' => 'API ticket',
+        ]);
+
+        $this->syncProjectPermissions($project, $writer, ['write', 'view']);
+
+        $this->withApplicationKey($writer)
+            ->patchJson(route('api.projects.tickets.update', [$project, $ticket]), [
+                'acceptance_criteria' => $ticket->acceptance_criteria,
+                'blocked_comment' => $ticket->blocked_comment,
+                'description' => $ticket->description,
+                'is_blocked' => $ticket->is_blocked,
+                'parent_ticket_id' => $ticket->parent_ticket_id,
+                'story_points' => $ticket->story_points,
+                'ticket_priority_id' => $priority->id,
+                'ticket_type_id' => $type->id,
+                'title' => 'Updated API ticket',
+            ])
+            ->assertOk()
+            ->assertJsonPath('data.author', null)
+            ->assertJsonPath('data.author_user_id', null);
+    }
+
+    public function test_ticket_options_only_return_project_visible_users(): void
+    {
+        [$user, $project] = $this->projectContext();
+        $projectViewer = User::factory()->create();
+        $outsider = User::factory()->create();
+
+        $this->syncProjectPermissions($project, $projectViewer, ['view']);
+
+        $response = $this->withApplicationKey($user)
+            ->getJson(route('api.projects.ticket-options', [
+                'project' => $project,
+                'source' => 'backlog',
+            ]))
+            ->assertOk();
+
+        $userIds = collect($response->json('data.users'))
+            ->pluck('id')
+            ->all();
+
+        $this->assertContains($user->id, $userIds);
+        $this->assertContains($projectViewer->id, $userIds);
+        $this->assertNotContains($outsider->id, $userIds);
+    }
+
     public function test_tickets_can_return_status_targets_and_move_statuses(): void
     {
         [$user, $project] = $this->projectContext();