diff --git a/.changeset/tame-groups-open.md b/.changeset/tame-groups-open.md
new file mode 100644
index 000000000..8be60d1dd
--- /dev/null
+++ b/.changeset/tame-groups-open.md
@@ -0,0 +1,5 @@
+---
+"braintrust": patch
+---
+
+Preserve dataset filters as arrays of clauses when creating experiments, allowing the experiment to store the original unnormalized filter form.
diff --git a/js/src/logger.test.ts b/js/src/logger.test.ts
index 21231d8e0..2d1775c61 100644
--- a/js/src/logger.test.ts
+++ b/js/src/logger.test.ts
@@ -484,7 +484,7 @@ function mockInitGitMetadata() {
   ).mockResolvedValue([]);
 }
 
-test("init forwards dataset _internal_btql to experiment register", async () => {
+test("init preserves dataset _internal_btql before experiment register", async () => {
   const state = await _exportsForTestingOnly.simulateLoginForTests();
 
   try {
@@ -504,7 +504,6 @@ test("init forwards dataset _internal_btql to experiment register", async () =>
         },
       ],
     };
-
     let experimentRegisterBody: unknown;
     vi.spyOn(state.appConn(), "post_json")
       .mockResolvedValueOnce({
@@ -564,7 +563,7 @@ test("init forwards dataset _internal_btql to experiment register", async () =>
   }
 });
 
-test("dataset fetch forwards _internal_btql filter arrays to btql", async () => {
+test("dataset fetch normalizes _internal_btql filter arrays before btql", async () => {
   const state = await _exportsForTestingOnly.simulateLoginForTests();
 
   try {
@@ -584,6 +583,13 @@ test("dataset fetch forwards _internal_btql filter arrays to btql", async () =>
       ],
       limit: 5,
     };
+    const normalizedDatasetFilter = {
+      filter: {
+        op: "and",
+        children: datasetFilter.filter,
+      },
+      limit: 5,
+    };
 
     vi.spyOn(state.appConn(), "post_json").mockResolvedValue({
       project: {
@@ -623,7 +629,7 @@ test("dataset fetch forwards _internal_btql filter arrays to btql", async () =>
     expect(btqlBody).toEqual(
       expect.objectContaining({
         query: expect.objectContaining({
-          filter: datasetFilter.filter,
+          filter: normalizedDatasetFilter.filter,
           limit: 5,
         }),
       }),
diff --git a/js/src/logger.ts b/js/src/logger.ts
index 81da807fe..4903f6c7e 100644
--- a/js/src/logger.ts
+++ b/js/src/logger.ts
@@ -3510,6 +3510,35 @@ function getExperimentDatasetFilter({
   return isObject(datasetFilter) ? datasetFilter : undefined;
 }
 
+function normalizeInternalBtqlFilter(
+  internalBtql?: Record<string, unknown>,
+): Record<string, unknown> | undefined {
+  if (internalBtql === undefined) {
+    return undefined;
+  }
+
+  const filter = internalBtql["filter"];
+  if (!Array.isArray(filter)) {
+    return internalBtql;
+  }
+
+  const { filter: _filter, ...internalBtqlWithoutFilter } = internalBtql;
+  if (filter.length === 0) {
+    return internalBtqlWithoutFilter;
+  }
+
+  return {
+    ...internalBtqlWithoutFilter,
+    filter:
+      filter.length === 1
+        ? filter[0]
+        : {
+            op: "and",
+            children: filter,
+          },
+  };
+}
+
 function getInternalBtqlLimit(
   internalBtql?: Record<string, unknown>,
 ): number | undefined {
@@ -6087,8 +6116,11 @@ export class ObjectFetcher<RecordType> implements AsyncIterable<
     const internalLimit = getInternalBtqlLimit(this._internal_btql);
     const limit =
       batchSize !== undefined ? batchSize : (internalLimit ?? batchLimit);
+    const normalizedInternalBtql = normalizeInternalBtqlFilter(
+      this._internal_btql,
+    );
     const internalBtqlWithoutReservedQueryKeys = Object.fromEntries(
-      Object.entries(this._internal_btql ?? {}).filter(
+      Object.entries(normalizedInternalBtql ?? {}).filter(
         ([key]) =>
           key !== "cursor" &&
           key !== "limit" &&