diff --git a/backend/src/cyclone/store.py b/backend/src/cyclone/store.py
new file mode 100644
index 0000000..ed64c1d
--- /dev/null
+++ b/backend/src/cyclone/store.py
@@ -0,0 +1,68 @@
+"""In-memory batch store for parsed X12 files.
+
+Lives at module scope so route handlers and tests can import a single
+singleton. Single-process only — no cross-process coordination. Threading:
+a re-entrant lock guards every public method so FastAPI's threadpool
+request handlers can call them concurrently.
+"""
+
+from __future__ import annotations
+
+import threading
+from datetime import datetime, timezone
+from typing import Iterable, Literal
+
+from pydantic import BaseModel, ConfigDict, Field
+
+from cyclone.parsers.models import ParseResult
+from cyclone.parsers.models_835 import ParseResult835
+
+
+BatchKind = Literal["837p", "835"]
+
+
+class BatchRecord(BaseModel):
+    """One parsed file, with a stable uuid4 id and the full ParseResult."""
+
+    model_config = ConfigDict(extra="ignore")
+
+    id: str
+    kind: BatchKind
+    input_filename: str
+    parsed_at: str  # ISO 8601 UTC, e.g. "2026-06-19T12:00:00Z"
+    result: ParseResult | ParseResult835 = Field(discriminator=None)
+
+
+class InMemoryStore:
+    """Thread-safe list of BatchRecord, newest-first on `list`."""
+
+    def __init__(self) -> None:
+        self._batches: list[BatchRecord] = []
+        self._lock = threading.RLock()
+
+    def add(self, record: BatchRecord) -> None:
+        with self._lock:
+            self._batches.append(record)
+
+    def list(self, *, limit: int = 100) -> list[BatchRecord]:
+        with self._lock:
+            return list(reversed(self._batches[-limit:]))
+
+    def get(self, batch_id: str) -> BatchRecord | None:
+        with self._lock:
+            for b in self._batches:
+                if b.id == batch_id:
+                    return b
+            return None
+
+    def all(self) -> list[BatchRecord]:
+        with self._lock:
+            return list(self._batches)
+
+
+store = InMemoryStore()
+
+
+def utcnow_iso() -> str:
+    """ISO 8601 UTC timestamp, second precision, suffixed with 'Z'."""
+    return datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
diff --git a/backend/tests/test_store.py b/backend/tests/test_store.py
new file mode 100644
index 0000000..61ed276
--- /dev/null
+++ b/backend/tests/test_store.py
@@ -0,0 +1,124 @@
+"""Tests for the in-memory batch store."""
+
+from __future__ import annotations
+
+from decimal import Decimal
+
+from cyclone.parsers.models import (
+    BatchSummary,
+    BillingProvider,
+    ClaimHeader,
+    ClaimOutput,
+    Envelope,
+    Payer,
+    ParseResult,
+    Subscriber,
+    ValidationIssue,
+    ValidationReport,
+)
+from cyclone.parsers.models_835 import ClaimPayment
+from cyclone.store import BatchRecord, InMemoryStore, store
+
+
+# ---------------------------------------------------------------------------
+# Stubs (match real model field names)
+# ---------------------------------------------------------------------------
+
+
+def _make_claim(claim_id: str = "CLM-1") -> ClaimOutput:
+    """Minimal ClaimOutput stub. Real parser not needed here."""
+    return ClaimOutput(
+        claim_id=claim_id,
+        control_number="0001",
+        transaction_date="2026-06-19",
+        billing_provider=BillingProvider(
+            name="Test",
+            npi="1234567890",
+            tax_id=None,
+            address=None,
+        ),
+        subscriber=Subscriber(
+            first_name="Jane",
+            last_name="Doe",
+            member_id="M1",
+            dob=None,
+            gender=None,
+            address=None,
+        ),
+        payer=Payer(name="Test Payer", id="P1"),
+        claim=ClaimHeader(
+            claim_id=claim_id,
+            total_charge=Decimal("0.00"),
+            place_of_service="11",
+            facility_code_qualifier=None,
+            frequency_code="1",
+            provider_signature=None,
+            assignment=None,
+            release_of_info=None,
+            prior_auth=None,
+        ),
+        diagnoses=[],
+        service_lines=[],
+        validation=ValidationReport(passed=True, errors=[], warnings=[]),
+        raw_segments=[],
+    )
+
+
+def _make_result() -> ParseResult:
+    return ParseResult(
+        envelope=Envelope(
+            sender_id="SENDER",
+            receiver_id="RECEIVER",
+            control_number="0001",
+            transaction_date="2026-06-19",
+            transaction_time=None,
+            implementation_guide=None,
+        ),
+        claims=[_make_claim("CLM-1")],
+        summary=BatchSummary(
+            input_file="test.txt",
+            control_number="0001",
+            transaction_date="2026-06-19",
+            total_claims=1,
+            passed=1,
+            failed=0,
+            failed_claim_ids=[],
+            issues_by_rule={},
+            output_dir=None,
+        ),
+    )
+
+
+# ---------------------------------------------------------------------------
+# Task 1: BatchRecord + InMemoryStore
+# ---------------------------------------------------------------------------
+
+
+def test_module_singleton_store_exists():
+    """The module-level `store` should be importable and be an InMemoryStore."""
+    assert isinstance(store, InMemoryStore)
+
+
+def test_in_memory_store_starts_empty():
+    s = InMemoryStore()
+    assert s.list() == []
+
+
+def test_add_and_get_round_trip():
+    s = InMemoryStore()
+    result = _make_result()
+    rec = BatchRecord(
+        id="abc123",
+        kind="837p",
+        input_filename="test.txt",
+        parsed_at="2026-06-19T12:00:00Z",
+        result=result,
+    )
+    s.add(rec)
+    assert s.get("abc123") is rec
+    assert s.list() == [rec]
+
+
+def test_get_missing_returns_none():
+    s = InMemoryStore()
+    assert s.get("does-not-exist") is None