diff --git a/backend/app/alembic/versions/38f0e8c8dc92_alter_unique_constraint_assistant_table.py b/backend/app/alembic/versions/38f0e8c8dc92_alter_unique_constraint_assistant_table.py
new file mode 100644
index 00000000..046aafbc
--- /dev/null
+++ b/backend/app/alembic/versions/38f0e8c8dc92_alter_unique_constraint_assistant_table.py
@@ -0,0 +1,47 @@
+"""Alter unique constraint assistant table
+
+Revision ID: 38f0e8c8dc92
+Revises: 5a59c6c29a82
+Create Date: 2025-08-20 15:02:39.151977
+
+"""
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel.sql.sqltypes
+
+
+# revision identifiers, used by Alembic.
+revision = "38f0e8c8dc92"
+down_revision = "5a59c6c29a82"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index("ix_openai_assistant_assistant_id", table_name="openai_assistant")
+    op.create_index(
+        op.f("ix_openai_assistant_assistant_id"),
+        "openai_assistant",
+        ["assistant_id"],
+        unique=False,
+    )
+    op.create_unique_constraint(
+        "uq_project_assistant_id", "openai_assistant", ["project_id", "assistant_id"]
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_constraint("uq_project_assistant_id", "openai_assistant", type_="unique")
+    op.drop_index(
+        op.f("ix_openai_assistant_assistant_id"), table_name="openai_assistant"
+    )
+    op.create_index(
+        "ix_openai_assistant_assistant_id",
+        "openai_assistant",
+        ["assistant_id"],
+        unique=True,
+    )
+    # ### end Alembic commands ###
diff --git a/backend/app/crud/assistants.py b/backend/app/crud/assistants.py
index 6a8e8e5b..62478aa5 100644
--- a/backend/app/crud/assistants.py
+++ b/backend/app/crud/assistants.py
@@ -173,8 +173,19 @@ def create_assistant(
 ) -> Assistant:
     verify_vector_store_ids_exist(openai_client, assistant.vector_store_ids)
 
+    assistant.assistant_id = assistant.assistant_id or str(uuid.uuid4())
+
+    existing = get_assistant_by_id(session, assistant.assistant_id, project_id)
+    if existing:
+        logger.error(
+            f"[create_assistant] Assistant with ID {mask_string(assistant.assistant_id)} already exists. | project_id: {project_id}"
+        )
+        raise HTTPException(
+            status_code=409,
+            detail=f"Assistant with ID {assistant.assistant_id} already exists.",
+        )
+
     assistant = Assistant(
-        assistant_id=str(uuid.uuid4()),
         **assistant.model_dump(exclude_unset=True),
         project_id=project_id,
         organization_id=organization_id,
diff --git a/backend/app/models/assistants.py b/backend/app/models/assistants.py
index b97e25b1..a67ae6be 100644
--- a/backend/app/models/assistants.py
+++ b/backend/app/models/assistants.py
@@ -3,13 +3,17 @@
 
 from sqlalchemy import Column, String, Text
 from sqlalchemy.dialects.postgresql import ARRAY
-from sqlmodel import Field, Relationship, SQLModel
+from sqlmodel import Field, Relationship, SQLModel, UniqueConstraint
 
 from app.core.util import now
 
 
 class AssistantBase(SQLModel):
-    assistant_id: str = Field(index=True, unique=True)
+    __table_args__ = (
+        UniqueConstraint("project_id", "assistant_id", name="uq_project_assistant_id"),
+    )
+
+    assistant_id: str = Field(index=True)
     name: str
     instructions: str = Field(sa_column=Column(Text, nullable=False))
     model: str
@@ -45,6 +49,12 @@ class AssistantCreate(SQLModel):
     instructions: str = Field(
         description="Instructions for the assistant", min_length=10
     )
+    assistant_id: str | None = Field(
+        default=None,
+        description="Unique identifier for the assistant",
+        min_length=3,
+        max_length=50,
+    )
     model: str = Field(
         default="gpt-4o",
         description="Model name for the assistant",
diff --git a/backend/app/tests/crud/test_assistants.py b/backend/app/tests/crud/test_assistants.py
index 322eed77..227fdb31 100644
--- a/backend/app/tests/crud/test_assistants.py
+++ b/backend/app/tests/crud/test_assistants.py
@@ -157,6 +157,74 @@ def test_create_assistant_success(self, mock_vector_store_ids_exist, db: Session
         assert result.temperature == assistant_create.temperature
         assert result.max_num_results == assistant_create.max_num_results
 
+    @patch("app.crud.assistants.verify_vector_store_ids_exist")
+    def test_create_assistant_with_id_success(
+        self, mock_vector_store_ids_exist, db: Session
+    ):
+        """Assistant is created with a specific ID when vector store IDs are valid"""
+        project = get_project(db)
+        assistant_create = AssistantCreate(
+            name="Test Assistant",
+            instructions="Test instructions",
+            model="gpt-4o",
+            vector_store_ids=["vs_1", "vs_2"],
+            temperature=0.7,
+            max_num_results=10,
+            assistant_id="test_assistant_id",
+        )
+        client = OpenAI(api_key="test_key")
+        mock_vector_store_ids_exist.return_value = None
+        result = create_assistant(
+            db, client, assistant_create, project.id, project.organization_id
+        )
+
+        assert result.name == assistant_create.name
+        assert result.instructions == assistant_create.instructions
+        assert result.model == assistant_create.model
+        assert result.vector_store_ids == assistant_create.vector_store_ids
+        assert result.temperature == assistant_create.temperature
+        assert result.max_num_results == assistant_create.max_num_results
+        assert result.assistant_id == assistant_create.assistant_id
+
+    @patch("app.crud.assistants.verify_vector_store_ids_exist")
+    def test_create_assistant_duplicate_assistant_id(
+        self, mock_vector_store_ids_exist, db: Session
+    ):
+        """Creating an assistant with a duplicate assistant_id should raise 409 Conflict"""
+        project = get_project(db)
+
+        assistant_id = "duplicate_id"
+        assistant_create_1 = AssistantCreate(
+            name="Assistant One",
+            instructions="First assistant instructions",
+            model="gpt-4o",
+            vector_store_ids=[],
+            assistant_id=assistant_id,
+        )
+        client = OpenAI(api_key="test_key")
+        mock_vector_store_ids_exist.return_value = None
+        create_assistant(
+            db, client, assistant_create_1, project.id, project.organization_id
+        )
+
+        assistant_create_2 = AssistantCreate(
+            name="Assistant Two",
+            instructions="Second assistant instructions",
+            model="gpt-4o",
+            vector_store_ids=[],
+            assistant_id=assistant_id,
+        )
+
+        with pytest.raises(HTTPException) as exc_info:
+            create_assistant(
+                db, client, assistant_create_2, project.id, project.organization_id
+            )
+
+        assert exc_info.value.status_code == 409
+        assert f"Assistant with ID {assistant_id} already exists." in str(
+            exc_info.value.detail
+        )
+
     @patch("app.crud.assistants.verify_vector_store_ids_exist")
     def test_create_assistant_vector_store_invalid(
         self, mock_vector_store_ids_exist, db: Session