diff --git a/components/history_embeddings/history_embeddings_service.cc b/components/history_embeddings/history_embeddings_service.cc
index e43a8d3d2526d2..5c44045300caee 100644
--- a/components/history_embeddings/history_embeddings_service.cc
+++ b/components/history_embeddings/history_embeddings_service.cc
@@ -423,8 +423,7 @@ void HistoryEmbeddingsService::OnQueryEmbeddingComputed(
           << (query_passages.empty() ? "(NONE)" : query_passages[0]) << "'";
 
   if (!succeeded) {
-    // Query embedding failed. Just return no search results.
-    std::move(callback).Run({});
+    std::move(callback).Run(std::move(result));
     return;
   }
 
diff --git a/components/history_embeddings/history_embeddings_service_unittest.cc b/components/history_embeddings/history_embeddings_service_unittest.cc
index 75a87af54c2537..4fa0e33f47860b 100644
--- a/components/history_embeddings/history_embeddings_service_unittest.cc
+++ b/components/history_embeddings/history_embeddings_service_unittest.cc
@@ -13,6 +13,7 @@
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/task/cancelable_task_tracker.h"
+#include "base/task/sequenced_task_runner.h"
 #include "base/test/bind.h"
 #include "base/test/metrics/histogram_tester.h"
 #include "base/test/scoped_feature_list.h"
@@ -53,6 +54,27 @@ base::FilePath GetTestFilePath(const std::string& file_name) {
       .AppendASCII(file_name);
 }
 
+class MockEmbedderWithDelay : public MockEmbedder {
+ public:
+  static constexpr base::TimeDelta kTimeout = base::Seconds(1);
+
+  MockEmbedderWithDelay() = default;
+  ~MockEmbedderWithDelay() override = default;
+
+  // Embedder:
+  void ComputePassagesEmbeddings(
+      passage_embeddings::PassagePriority priority,
+      std::vector<std::string> passages,
+      ComputePassagesEmbeddingsCallback callback) override {
+    base::SequencedTaskRunner::GetCurrentDefault()->PostDelayedTask(
+        FROM_HERE,
+        base::BindOnce(std::move(callback), std::move(passages),
+                       ComputeEmbeddingsForPassages(passages),
+                       passage_embeddings::ComputeEmbeddingsStatus::kSuccess),
+        kTimeout);
+  }
+};
+
 }  // namespace
 
 class HistoryEmbeddingsServicePublic : public HistoryEmbeddingsService {
@@ -79,6 +101,7 @@ class HistoryEmbeddingsServicePublic : public HistoryEmbeddingsService {
   using HistoryEmbeddingsService::OnPassagesEmbeddingsComputed;
   using HistoryEmbeddingsService::OnSearchCompleted;
   using HistoryEmbeddingsService::QueryIsFiltered;
+  using HistoryEmbeddingsService::RebuildAbsentEmbeddings;
 
   using HistoryEmbeddingsService::answerer_;
   using HistoryEmbeddingsService::embedder_metadata_;
@@ -116,7 +139,8 @@ class HistoryEmbeddingsServiceTest : public testing::Test {
         os_crypt_.get(), history_service_.get(),
         page_content_annotations_service_.get(),
         /*optimization_guide_decider=*/nullptr,
-        std::make_unique<MockEmbedder>(), std::make_unique<MockAnswerer>(),
+        std::make_unique<MockEmbedderWithDelay>(),
+        std::make_unique<MockAnswerer>(),
         std::make_unique<MockIntentClassifier>());
 
     ASSERT_TRUE(listener()->filter_words_hashes().empty());
@@ -204,7 +228,8 @@ class HistoryEmbeddingsServiceTest : public testing::Test {
                               false);
   }
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::TaskEnvironment task_environment_{
+      base::test::TaskEnvironment::TimeSource::MOCK_TIME};
 
   base::ScopedTempDir history_dir_;
   std::unique_ptr<os_crypt_async::OSCryptAsync> os_crypt_;
@@ -1016,7 +1041,6 @@ class AddSyncedVisitTask : public history::HistoryDBTask {
     history::VisitID visit_id = backend->AddSyncedVisit(
         url_, u"Title", /*hidden=*/false, visit_, std::nullopt, std::nullopt);
     EXPECT_NE(visit_id, history::kInvalidVisitID);
-    LOG(ERROR) << "Added visit!";
     return true;
   }
 
@@ -1080,4 +1104,173 @@ TEST_F(HistoryEmbeddingsServiceTest, SearchGetsIfUrlIsKnownToSync) {
   EXPECT_EQ(result.scored_url_rows[1].is_url_known_to_sync, true);
 }
 
+TEST_F(HistoryEmbeddingsServiceTest, CancelPreviousSearches) {
+  base::Time now = base::Time::Now();
+  AddTestHistoryPage("http://test1.com");
+  OnPassagesEmbeddingsComputed(UrlData(1, 1, now),
+                               {"test passage 1", "test passage 2"},
+                               {Embedding(std::vector<float>(768, 1.0f)),
+                                Embedding(std::vector<float>(768, 1.0f))},
+                               ComputeEmbeddingsStatus::kSuccess);
+  OverrideVisibilityScoresForTesting({
+      {"test passage 1", 0.99},
+      {"test passage 2", 0.99},
+  });
+  // Service uses the default .9 score threshold when neither the feature param
+  // nor the metadata thresholds are set.
+  SetMetadataScoreThreshold(0.01);
+
+  base::test::TestFuture<SearchResult> future1;
+  service_->Search(nullptr, "passage", {}, 3, /*skip_answering=*/true,
+                   future1.GetRepeatingCallback());
+
+  base::test::TestFuture<SearchResult> future2;
+  service_->Search(nullptr, "passage", {}, 3, /*skip_answering=*/true,
+                   future2.GetRepeatingCallback());
+
+  base::test::TestFuture<SearchResult> future3;
+  service_->Search(nullptr, "passage", {}, 3, /*skip_answering=*/true,
+                   future3.GetRepeatingCallback());
+
+  base::test::TestFuture<SearchResult> future4;
+  service_->Search(nullptr, "passage", {}, 3, /*skip_answering=*/true,
+                   future4.GetRepeatingCallback());
+
+  // The first query is processed.
+  // TODO(crbug.com/390241271): The first query should NOT be processed.
+  SearchResult result1 = future1.Take();
+  EXPECT_FALSE(result1.session_id.empty());
+  EXPECT_EQ(result1.query, "passage");
+  ASSERT_EQ(result1.scored_url_rows.size(), 1u);
+  EXPECT_EQ(result1.scored_url_rows[0].scored_url.url_id, 1);
+  EXPECT_EQ(result1.scored_url_rows[0].scored_url.visit_id, 1);
+  EXPECT_EQ(result1.scored_url_rows[0].scored_url.visit_time, now);
+
+  // The second query is skipped.
+  SearchResult result2 = future2.Take();
+  EXPECT_FALSE(result2.session_id.empty());
+  EXPECT_EQ(result2.query, "passage");
+  ASSERT_EQ(result2.scored_url_rows.size(), 0u);
+
+  // The third query is skipped.
+  SearchResult result3 = future3.Take();
+  EXPECT_FALSE(result3.session_id.empty());
+  EXPECT_EQ(result3.query, "passage");
+  ASSERT_EQ(result3.scored_url_rows.size(), 0u);
+
+  // The last query is processed.
+  SearchResult result4 = future4.Take();
+  EXPECT_FALSE(result4.session_id.empty());
+  EXPECT_EQ(result4.query, "passage");
+  ASSERT_EQ(result4.scored_url_rows.size(), 1u);
+  EXPECT_EQ(result4.scored_url_rows[0].scored_url.url_id, 1);
+  EXPECT_EQ(result4.scored_url_rows[0].scored_url.visit_id, 1);
+  EXPECT_EQ(result4.scored_url_rows[0].scored_url.visit_time, now);
+}
+
+TEST_F(HistoryEmbeddingsServiceTest, UseDatabaseBeforeEmbedder) {
+  base::test::TestFuture<UrlData> store_future;
+  service_->SetPassagesStoredCallbackForTesting(
+      store_future.GetRepeatingCallback());
+
+  base::Time now = base::Time::Now();
+  AddTestHistoryPage("http://test1.com");
+
+  // TODO(crbug.com/390241271): Enable erasing non-ascii characters.
+
+  {
+    // TODO(crbug.com/390241271): Test with an empty passage.
+    base::HistogramTester histogram_tester;
+    service_->ComputeAndStorePassageEmbeddings(
+        /*url_id=*/1,
+        /*visit_id=*/1,
+        /*visit_time=*/now + base::Seconds(1),
+        {
+            "test passage 1",
+            "test passage ß",
+            "ßßß",
+        });
+
+    UrlData url_data = store_future.Take();
+    ASSERT_EQ(url_data.passages.passages_size(), 3);
+    ASSERT_EQ(url_data.embeddings.size(), 3u);
+    ASSERT_EQ(url_data.passages.passages(0), "test passage 1");
+    ASSERT_EQ(url_data.embeddings[0].Dimensions(), 768u);
+    ASSERT_EQ(url_data.passages.passages(1), "test passage ß");
+    ASSERT_EQ(url_data.embeddings[1].Dimensions(), 768u);
+    ASSERT_EQ(url_data.passages.passages(2), "ßßß");
+    ASSERT_EQ(url_data.embeddings[2].Dimensions(), 768u);
+
+    // The cache wasn't used because there was no existing data.
+    histogram_tester.ExpectTotalCount(
+        "History.Embeddings.DatabaseCachedPassageTryCount", 1);
+    histogram_tester.ExpectBucketCount(
+        "History.Embeddings.DatabaseCachedPassageTryCount", 3, 1);
+    histogram_tester.ExpectTotalCount(
+        "History.Embeddings.DatabaseCachedPassageHitCount", 1);
+    histogram_tester.ExpectBucketCount(
+        "History.Embeddings.DatabaseCachedPassageHitCount", 0, 1);
+  }
+  {
+    // TODO(crbug.com/390241271): Test with an empty passage.
+    base::HistogramTester histogram_tester;
+    service_->ComputeAndStorePassageEmbeddings(
+        /*url_id=*/1,
+        /*visit_id=*/2,
+        /*visit_time=*/now + base::Minutes(1),
+        {
+            "test passage 1",
+            "test passage ßßß",
+            "ßßß",
+        });
+
+    UrlData url_data = store_future.Take();
+    ASSERT_EQ(url_data.passages.passages_size(), 3);
+    ASSERT_EQ(url_data.embeddings.size(), 3u);
+    ASSERT_EQ(url_data.passages.passages(0), "test passage 1");
+    ASSERT_EQ(url_data.embeddings[0].Dimensions(), 768u);
+    ASSERT_EQ(url_data.passages.passages(1), "test passage ßßß");
+    ASSERT_EQ(url_data.embeddings[1].Dimensions(), 768u);
+    ASSERT_EQ(url_data.passages.passages(2), "ßßß");
+    ASSERT_EQ(url_data.embeddings[2].Dimensions(), 768u);
+
+    // The cache was used because there was existing data.
+    histogram_tester.ExpectTotalCount(
+        "History.Embeddings.DatabaseCachedPassageTryCount", 1);
+    histogram_tester.ExpectBucketCount(
+        "History.Embeddings.DatabaseCachedPassageTryCount", 3, 1);
+    histogram_tester.ExpectTotalCount(
+        "History.Embeddings.DatabaseCachedPassageHitCount", 1);
+    histogram_tester.ExpectBucketCount(
+        "History.Embeddings.DatabaseCachedPassageHitCount", 2, 1);
+  }
+}
+
+TEST_F(HistoryEmbeddingsServiceTest, RebuildAbsentEmbeddings) {
+  base::HistogramTester histogram_tester;
+
+  base::test::TestFuture<UrlData> store_future;
+  service_->SetPassagesStoredCallbackForTesting(
+      store_future.GetRepeatingCallback());
+
+  // TODO(crbug.com/390241271): Enable erasing non-ascii characters.
+  // TODO(crbug.com/390241271): Test with an empty passage.
+
+  UrlData existing_url_data_1(1, 1, base::Time::Now());
+  existing_url_data_1.passages.add_passages("test passage 1");
+  existing_url_data_1.passages.add_passages("test passage ßßß");
+  existing_url_data_1.passages.add_passages("ßßß");
+  service_->RebuildAbsentEmbeddings({existing_url_data_1});
+
+  UrlData url_data = store_future.Take();
+  ASSERT_EQ(url_data.passages.passages_size(), 3);
+  ASSERT_EQ(url_data.embeddings.size(), 3u);
+  ASSERT_EQ(url_data.passages.passages(0), "test passage 1");
+  ASSERT_EQ(url_data.embeddings[0].Dimensions(), 768u);
+  ASSERT_EQ(url_data.passages.passages(1), "test passage ßßß");
+  ASSERT_EQ(url_data.embeddings[1].Dimensions(), 768u);
+  ASSERT_EQ(url_data.passages.passages(2), "ßßß");
+  ASSERT_EQ(url_data.embeddings[2].Dimensions(), 768u);
+}
+
 }  // namespace history_embeddings
diff --git a/components/history_embeddings/mock_embedder.cc b/components/history_embeddings/mock_embedder.cc
index a024aed4ea623b..73b07f408692a1 100644
--- a/components/history_embeddings/mock_embedder.cc
+++ b/components/history_embeddings/mock_embedder.cc
@@ -22,12 +22,6 @@ Embedding ComputeEmbeddingForPassage(const std::string& passage) {
   return embedding;
 }
 
-std::vector<Embedding> ComputeEmbeddingsForPassages(
-    const std::vector<std::string>& passages) {
-  return std::vector<Embedding>(passages.size(),
-                                ComputeEmbeddingForPassage(""));
-}
-
 }  // namespace
 
 MockEmbedder::MockEmbedder() = default;
@@ -49,4 +43,10 @@ void MockEmbedder::SetOnEmbedderReady(OnEmbedderReadyCallback callback) {
   std::move(callback).Run({kModelVersion, kOutputSize});
 }
 
+std::vector<Embedding> MockEmbedder::ComputeEmbeddingsForPassages(
+    const std::vector<std::string>& passages) {
+  return std::vector<Embedding>(passages.size(),
+                                ComputeEmbeddingForPassage(""));
+}
+
 }  // namespace history_embeddings
diff --git a/components/history_embeddings/mock_embedder.h b/components/history_embeddings/mock_embedder.h
index 4f5b6114e49ff6..52eb2ad2073c20 100644
--- a/components/history_embeddings/mock_embedder.h
+++ b/components/history_embeddings/mock_embedder.h
@@ -5,6 +5,9 @@
 #ifndef COMPONENTS_HISTORY_EMBEDDINGS_MOCK_EMBEDDER_H_
 #define COMPONENTS_HISTORY_EMBEDDINGS_MOCK_EMBEDDER_H_
 
+#include <string>
+#include <vector>
+
 #include "components/history_embeddings/embedder.h"
 
 namespace history_embeddings {
@@ -21,6 +24,10 @@ class MockEmbedder : public Embedder {
       ComputePassagesEmbeddingsCallback callback) override;
 
   void SetOnEmbedderReady(OnEmbedderReadyCallback callback) override;
+
+ protected:
+  std::vector<Embedding> ComputeEmbeddingsForPassages(
+      const std::vector<std::string>& passages);
 };
 
 }  // namespace history_embeddings