diff --git a/backend/alembic/versions/e2d81e82ea5e_add_ai_chat_sessions_table.py b/backend/alembic/versions/e2d81e82ea5e_add_ai_chat_sessions_table.py
new file mode 100644
index 00000000..42d2264c
--- /dev/null
+++ b/backend/alembic/versions/e2d81e82ea5e_add_ai_chat_sessions_table.py
@@ -0,0 +1,46 @@
+"""add ai_chat_sessions table
+
+Revision ID: e2d81e82ea5e
+Revises: 1490781700bc
+Create Date: 2026-02-27 03:41:33.832260
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'e2d81e82ea5e'
+down_revision: Union[str, None] = '1490781700bc'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "ai_chat_sessions",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True),
+        sa.Column("user_id", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True),
+        sa.Column("account_id", UUID(as_uuid=True), sa.ForeignKey("accounts.id", ondelete="CASCADE"), nullable=False, index=True),
+        sa.Column("status", sa.String(20), nullable=False, server_default="active"),
+        sa.Column("current_phase", sa.String(20), nullable=False, server_default="scoping"),
+        sa.Column("flow_type", sa.String(20), nullable=False),
+        sa.Column("conversation_history", JSONB, nullable=False, server_default="[]"),
+        sa.Column("working_tree", JSONB, nullable=True),
+        sa.Column("tree_metadata", JSONB, nullable=False, server_default="{}"),
+        sa.Column("provider_used", sa.String(20), nullable=True),
+        sa.Column("message_count", sa.Integer, nullable=False, server_default="0"),
+        sa.Column("total_input_tokens", sa.Integer, nullable=False, server_default="0"),
+        sa.Column("total_output_tokens", sa.Integer, nullable=False, server_default="0"),
+        sa.Column("generated_tree_id", UUID(as_uuid=True), sa.ForeignKey("trees.id", ondelete="SET NULL"), nullable=True),
+        sa.Column("expires_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("ai_chat_sessions")
diff --git a/backend/app/models/__init__.py b/backend/app/models/__init__.py
index 3731740b..3748d9c8 100644
--- a/backend/app/models/__init__.py
+++ b/backend/app/models/__init__.py
@@ -28,6 +28,7 @@ from .maintenance_schedule import MaintenanceSchedule
 from .feedback import Feedback
 from .ai_conversation import AIConversation
 from .ai_usage import AIUsage
+from .ai_chat_session import AIChatSession
 
 __all__ = [
     "User",
@@ -67,4 +68,5 @@ __all__ = [
     "Feedback",
     "AIConversation",
     "AIUsage",
+    "AIChatSession",
 ]
diff --git a/backend/app/models/ai_chat_session.py b/backend/app/models/ai_chat_session.py
new file mode 100644
index 00000000..8fbde1c6
--- /dev/null
+++ b/backend/app/models/ai_chat_session.py
@@ -0,0 +1,88 @@
+"""AI Chat Builder session tracking.
+
+Stores conversational flow builder state across the multi-phase interview.
+Sessions expire after 24 hours.
+"""
+import uuid
+from datetime import datetime, timezone
+from typing import Optional, Any
+
+from sqlalchemy import String, DateTime, ForeignKey, Integer
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+from app.core.database import Base
+
+
+class AIChatSession(Base):
+    __tablename__ = "ai_chat_sessions"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    status: Mapped[str] = mapped_column(
+        String(20),
+        nullable=False,
+        default="active",
+        comment="active | completed | abandoned",
+    )
+    current_phase: Mapped[str] = mapped_column(
+        String(20),
+        nullable=False,
+        default="scoping",
+        comment="scoping | discovery | enrichment | review | generation",
+    )
+    flow_type: Mapped[str] = mapped_column(
+        String(20),
+        nullable=False,
+        comment="troubleshooting | procedural",
+    )
+    conversation_history: Mapped[list[dict[str, Any]]] = mapped_column(
+        JSONB, nullable=False, default=list
+    )
+    working_tree: Mapped[Optional[dict[str, Any]]] = mapped_column(
+        JSONB, nullable=True
+    )
+    tree_metadata: Mapped[dict[str, Any]] = mapped_column(
+        JSONB, nullable=False, default=dict
+    )
+    provider_used: Mapped[Optional[str]] = mapped_column(
+        String(20), nullable=True
+    )
+    message_count: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0
+    )
+    total_input_tokens: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0
+    )
+    total_output_tokens: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0
+    )
+    generated_tree_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("trees.id", ondelete="SET NULL"),
+        nullable=True,
+    )
+    expires_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc),
+        onupdate=lambda: datetime.now(timezone.utc),
+    )