diff --git a/test/Api.IntegrationTest/AdminConsole/Controllers/OrganizationUsersControllerAcceptInitTests.cs b/test/Api.IntegrationTest/AdminConsole/Controllers/OrganizationUsersControllerAcceptInitTests.cs
new file mode 100644
index 0000000000..4b079370c8
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+++ b/test/Api.IntegrationTest/AdminConsole/Controllers/OrganizationUsersControllerAcceptInitTests.cs
@@ -0,0 +1,309 @@
+using System.Net;
+using Bit.Api.AdminConsole.Models.Request.Organizations;
+using Bit.Api.IntegrationTest.Factories;
+using Bit.Api.IntegrationTest.Helpers;
+using Bit.Core.AdminConsole.Entities;
+using Bit.Core.Auth.Models.Business.Tokenables;
+using Bit.Core.Billing.Enums;
+using Bit.Core.Entities;
+using Bit.Core.Enums;
+using Bit.Core.Repositories;
+using Bit.Core.Tokens;
+using Xunit;
+
+namespace Bit.Api.IntegrationTest.AdminConsole.Controllers;
+
+/// <summary>
+/// Integration tests for the AcceptInit endpoint (POST /organizations/{orgId}/users/{organizationUserId}/accept-init).
+/// This endpoint is used when a user accepts an invitation to a pending organization, initializing the organization
+/// by setting its keys and status, accepting the user's invitation, and confirming the user as a member.
+/// </summary>
+public class OrganizationUsersControllerAcceptInitTests : IClassFixture<ApiApplicationFactory>, IAsyncLifetime
+{
+    private const string _mockEncryptedString = "2.AOs41Hd8OQiCPXjyJKCiDA==|O6OHgt2U2hJGBSNGnimJmg==|iD33s8B69C8JhYYhSa4V1tArjvLr8eEaGqOV7BRo5Jk=";
+    private const string _mockPublicKey = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAwMj7W00xS7H0NWasGn7PfEq8VfH3fa5XuZucsKxLLRAHHZk0xGRZJH2lFIznizv3GpF8vzhHhe9VpmMkrdIa5oWhwHpy+D7Z1QCQxuUXzvMKpa95GOntr89nN/mWKpk6abjgjmDcqFJ0lhDqkKnDfes+d8BBd5oEA8p41/Ykz7OfG7AiktVBpTQFW09MQh1NOvcLxVgiUUVRPwNRKrOeCekWDtOjZhASMETv3kI1ogvhHukOQ3ztDzrxvmwnLQ+cXl1EeD8gQnGDp3QLiJqxPgh2EdmANh4IzjRexoDn6BqhRGqLLIoLAbbkoiNrd6NYujrWW0N8KMMoVEXuJL2g4wIDAQAB";
+    private const string _mockEncryptedPrivateKey = "2.Ytudv+Qk3ET9hN8whqpuGg==|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|euhiXWXehYbFQhlAV6LIECSIPCIRaHbNdr9OI4cTPUM=";
+
+    private readonly HttpClient _client;
+    private readonly ApiApplicationFactory _factory;
+    private readonly LoginHelper _loginHelper;
+
+    private Organization _pendingOrganization = null!;
+    private User _invitedUser = null!;
+    private OrganizationUser _invitedOrgUser = null!;
+    private string _invitedUserEmail = null!;
+
+    public OrganizationUsersControllerAcceptInitTests(ApiApplicationFactory apiFactory)
+    {
+        _factory = apiFactory;
+        _client = _factory.CreateClient();
+        _loginHelper = new LoginHelper(_factory, _client);
+    }
+
+    public async Task InitializeAsync()
+    {
+        // Create a pending organization without keys
+        var organizationRepository = _factory.GetService<IOrganizationRepository>();
+        _pendingOrganization = new Organization
+        {
+            Name = "Pending Test Org",
+            BillingEmail = $"{Guid.NewGuid()}@example.com",
+            Plan = "Free",
+            PlanType = PlanType.Free,
+            Enabled = false,
+            Status = OrganizationStatusType.Pending,
+            PublicKey = null,
+            PrivateKey = null,
+            CreationDate = DateTime.UtcNow,
+            RevisionDate = DateTime.UtcNow
+        };
+        await organizationRepository.CreateAsync(_pendingOrganization);
+
+        // Create a user who will be invited to the pending organization
+        _invitedUserEmail = $"{Guid.NewGuid()}@example.com";
+        await _factory.LoginWithNewAccount(_invitedUserEmail);
+
+        var userRepository = _factory.GetService<IUserRepository>();
+        _invitedUser = await userRepository.GetByEmailAsync(_invitedUserEmail);
+
+        // Create organization user as invited (not yet accepted)
+        // Note: UserId should be NULL for invited users who haven't accepted yet
+        var organizationUserRepository = _factory.GetService<IOrganizationUserRepository>();
+        _invitedOrgUser = new OrganizationUser
+        {
+            OrganizationId = _pendingOrganization.Id,
+            UserId = null,  // NULL until they accept
+            Email = _invitedUserEmail,
+            Key = null,
+            Type = OrganizationUserType.Owner,
+            Status = OrganizationUserStatusType.Invited,
+            AccessSecretsManager = false
+        };
+        await organizationUserRepository.CreateAsync(_invitedOrgUser);
+    }
+
+    public Task DisposeAsync()
+    {
+        _client.Dispose();
+        return Task.CompletedTask;
+    }
+
+    [Fact]
+    public async Task AcceptInit_WithValidData_InitializesOrganizationAndConfirmsUser()
+    {
+        // Arrange
+        await _loginHelper.LoginAsync(_invitedUserEmail);
+
+        var token = GenerateInviteToken(_invitedOrgUser, _invitedUser.Email);
+
+        var acceptInitRequest = new OrganizationUserAcceptInitRequestModel
+        {
+            Token = token,
+            Key = "test-user-key",
+            Keys = new OrganizationKeysRequestModel
+            {
+                PublicKey = _mockPublicKey,
+                EncryptedPrivateKey = _mockEncryptedPrivateKey
+            },
+            CollectionName = _mockEncryptedString
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync(
+            $"organizations/{_pendingOrganization.Id}/users/{_invitedOrgUser.Id}/accept-init",
+            acceptInitRequest);
+
+        // Assert
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        // Verify organization was initialized
+        var organizationRepository = _factory.GetService<IOrganizationRepository>();
+        var updatedOrganization = await organizationRepository.GetByIdAsync(_pendingOrganization.Id);
+
+        Assert.NotNull(updatedOrganization);
+        Assert.True(updatedOrganization.Enabled);
+        Assert.Equal(OrganizationStatusType.Created, updatedOrganization.Status);
+        Assert.Equal(_mockPublicKey, updatedOrganization.PublicKey);
+        Assert.Equal(_mockEncryptedPrivateKey, updatedOrganization.PrivateKey);
+
+        // Verify user was confirmed
+        var organizationUserRepository = _factory.GetService<IOrganizationUserRepository>();
+        var confirmedOrgUser = await organizationUserRepository.GetByIdAsync(_invitedOrgUser.Id);
+
+        Assert.NotNull(confirmedOrgUser);
+        Assert.Equal(OrganizationUserStatusType.Confirmed, confirmedOrgUser.Status);
+        Assert.Equal("test-user-key", confirmedOrgUser.Key);
+
+        // Verify default collection was created
+        var collectionRepository = _factory.GetService<ICollectionRepository>();
+        var collections = await collectionRepository.GetManyByOrganizationIdAsync(_pendingOrganization.Id);
+
+        Assert.Single(collections);
+        Assert.Equal(_mockEncryptedString, collections.First().Name);
+        Assert.Equal(_pendingOrganization.Id, collections.First().OrganizationId);
+
+        // Verify user has access to the collection
+        var (_, collectionAccess) = await organizationUserRepository.GetByIdWithCollectionsAsync(_invitedOrgUser.Id);
+        Assert.Single(collectionAccess);
+        Assert.Equal(collections.First().Id, collectionAccess.First().Id);
+        Assert.True(collectionAccess.First().Manage);
+        Assert.False(collectionAccess.First().ReadOnly);
+        Assert.False(collectionAccess.First().HidePasswords);
+    }
+
+    [Fact]
+    public async Task AcceptInit_WithoutCollectionName_InitializesOrganizationWithoutCreatingCollection()
+    {
+        // Arrange
+        await _loginHelper.LoginAsync(_invitedUserEmail);
+
+        var token = GenerateInviteToken(_invitedOrgUser, _invitedUser.Email);
+
+        var acceptInitRequest = new OrganizationUserAcceptInitRequestModel
+        {
+            Token = token,
+            Key = "test-user-key",
+            Keys = new OrganizationKeysRequestModel
+            {
+                PublicKey = _mockPublicKey,
+                EncryptedPrivateKey = _mockEncryptedPrivateKey
+            },
+            CollectionName = null
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync(
+            $"organizations/{_pendingOrganization.Id}/users/{_invitedOrgUser.Id}/accept-init",
+            acceptInitRequest);
+
+        // Assert
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        // Verify organization was initialized
+        var organizationRepository = _factory.GetService<IOrganizationRepository>();
+        var updatedOrganization = await organizationRepository.GetByIdAsync(_pendingOrganization.Id);
+
+        Assert.NotNull(updatedOrganization);
+        Assert.True(updatedOrganization.Enabled);
+        Assert.Equal(OrganizationStatusType.Created, updatedOrganization.Status);
+
+        // Verify user was confirmed
+        var organizationUserRepository = _factory.GetService<IOrganizationUserRepository>();
+        var confirmedOrgUser = await organizationUserRepository.GetByIdAsync(_invitedOrgUser.Id);
+
+        Assert.NotNull(confirmedOrgUser);
+        Assert.Equal(OrganizationUserStatusType.Confirmed, confirmedOrgUser.Status);
+
+        // Verify NO collection was created
+        var collectionRepository = _factory.GetService<ICollectionRepository>();
+        var collections = await collectionRepository.GetManyByOrganizationIdAsync(_pendingOrganization.Id);
+
+        Assert.Empty(collections);
+    }
+
+    [Fact]
+    public async Task AcceptInit_WithInvalidToken_ReturnsBadRequest()
+    {
+        // Arrange
+        await _loginHelper.LoginAsync(_invitedUserEmail);
+
+        var acceptInitRequest = new OrganizationUserAcceptInitRequestModel
+        {
+            Token = "invalid-token",
+            Key = "test-user-key",
+            Keys = new OrganizationKeysRequestModel
+            {
+                PublicKey = _mockPublicKey,
+                EncryptedPrivateKey = _mockEncryptedPrivateKey
+            },
+            CollectionName = _mockEncryptedString
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync(
+            $"organizations/{_pendingOrganization.Id}/users/{_invitedOrgUser.Id}/accept-init",
+            acceptInitRequest);
+
+        // Assert
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+
+        // Verify organization was NOT initialized
+        var organizationRepository = _factory.GetService<IOrganizationRepository>();
+        var organization = await organizationRepository.GetByIdAsync(_pendingOrganization.Id);
+
+        Assert.False(organization.Enabled);
+        Assert.Equal(OrganizationStatusType.Pending, organization.Status);
+        Assert.Null(organization.PublicKey);
+        Assert.Null(organization.PrivateKey);
+    }
+
+    [Fact]
+    public async Task AcceptInit_WithAlreadyEnabledOrganization_ReturnsBadRequest()
+    {
+        // Arrange
+        // Update the organization to be already enabled
+        var organizationRepository = _factory.GetService<IOrganizationRepository>();
+        _pendingOrganization.Enabled = true;
+        _pendingOrganization.Status = OrganizationStatusType.Created;
+        await organizationRepository.ReplaceAsync(_pendingOrganization);
+
+        await _loginHelper.LoginAsync(_invitedUserEmail);
+
+        var token = GenerateInviteToken(_invitedOrgUser, _invitedUser.Email);
+
+        var acceptInitRequest = new OrganizationUserAcceptInitRequestModel
+        {
+            Token = token,
+            Key = "test-user-key",
+            Keys = new OrganizationKeysRequestModel
+            {
+                PublicKey = _mockPublicKey,
+                EncryptedPrivateKey = _mockEncryptedPrivateKey
+            },
+            CollectionName = _mockEncryptedString
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync(
+            $"organizations/{_pendingOrganization.Id}/users/{_invitedOrgUser.Id}/accept-init",
+            acceptInitRequest);
+
+        // Assert
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task AcceptInit_WithoutAuthentication_ReturnsUnauthorized()
+    {
+        // Arrange - don't log in
+        var token = GenerateInviteToken(_invitedOrgUser, _invitedUser.Email);
+
+        var acceptInitRequest = new OrganizationUserAcceptInitRequestModel
+        {
+            Token = token,
+            Key = "test-user-key",
+            Keys = new OrganizationKeysRequestModel
+            {
+                PublicKey = _mockPublicKey,
+                EncryptedPrivateKey = _mockEncryptedPrivateKey
+            },
+            CollectionName = _mockEncryptedString
+        };
+
+        // Act
+        var response = await _client.PostAsJsonAsync(
+            $"organizations/{_pendingOrganization.Id}/users/{_invitedOrgUser.Id}/accept-init",
+            acceptInitRequest);
+
+        // Assert
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    private string GenerateInviteToken(OrganizationUser orgUser, string email)
+    {
+        var tokenFactory = _factory.GetService<IDataProtectorTokenFactory<OrgUserInviteTokenable>>();
+
+        var tokenable = new OrgUserInviteTokenable(orgUser);
+        return tokenFactory.Protect(tokenable);
+    }
+}