diff --git a/src/Http/Controllers/Api/AnnotationCandidateController.php b/src/Http/Controllers/Api/AnnotationCandidateController.php
index 301b387..1b73fd1 100644
--- a/src/Http/Controllers/Api/AnnotationCandidateController.php
+++ b/src/Http/Controllers/Api/AnnotationCandidateController.php
@@ -88,34 +88,47 @@ public function indexSimilar($id, $id2)
         $job = MaiaJob::findOrFail($id);
         $this->authorize('access', $job);
 
-        $feature = AnnotationCandidateFeatureVector::where('job_id', $id)
-            ->findOrFail($id2);
-
-        // Manually optimized query for the cosine distance. The nearestNeighbors()
-        // method of pgvector seems to compute the distances twice and returns lots
-        // of data that we don't need.
-        $ids = $feature->whereNotNull('vector')
-            ->where('id', '!=', $feature->id)
-            ->where('job_id', $id)
-            ->orderByRaw('vector <=> ?', [$feature->vector])
-            ->pluck('id');
-
-        $count = $ids->count();
-        if ($count === 0) {
+        $feature = AnnotationCandidateFeatureVector::findOrFail($id2);
+        $query = AnnotationCandidateFeatureVector::where('job_id', $id);
+        $hasFeatures = $query->clone()
+            ->whereNotNull('vector')
+            ->whereNot('id', $id2)
+            ->exists();
+
+        if (!$hasFeatures) {
             abort(Response::HTTP_NOT_FOUND);
         }
 
-        if ($count !== ($job->annotationCandidates()->count() - 1)) {
+        $yieldItems = function () use ($query, $feature, $job): \Generator {
+            // Manually optimized query for the cosine distance. The nearestNeighbors()
+            // method of pgvector seems to compute the distances twice and returns lots
+            // of data that we don't need.
+            $idsQuery = $query->clone()
+                ->whereNotNull('vector')
+                ->whereNot('id', $feature->id)
+                ->orderByRaw('vector <=> ?', [$feature->vector])
+                ->orderBy('id')
+                ->select('id');
+
+            foreach ($idsQuery->lazy() as $item) {
+                yield $item->id;
+            }
+
             // Add IDs of candidates without feature vectors at the end.
-            $ids = $ids->concat(
-                $job->annotationCandidates()
-                    ->whereNotIn('id', $ids)
-                    ->whereNot('id', $id2)
-                    ->pluck('id')
-            );
-        }
+            $remainingIdsQuery = $job->annotationCandidates()
+                ->whereNotIn('id', function ($query) use ($job) {
+                    $query->select('id')
+                        ->from('maia_annotation_candidate_feature_vectors')
+                        ->where('job_id', $job->id);
+                });
+
+            foreach ($remainingIdsQuery->lazyById() as $item) {
+                yield $item->id;
+            }
+        };
 
-        return $ids;
+        // Use a streamed response because there can be a lot of items.
+        return response()->streamJson($yieldItems());
     }
 
     /**
diff --git a/src/Http/Controllers/Api/TrainingProposalController.php b/src/Http/Controllers/Api/TrainingProposalController.php
index 86d5676..97d85e2 100644
--- a/src/Http/Controllers/Api/TrainingProposalController.php
+++ b/src/Http/Controllers/Api/TrainingProposalController.php
@@ -85,34 +85,47 @@ public function indexSimilar($id, $id2)
         $job = MaiaJob::findOrFail($id);
         $this->authorize('access', $job);
 
-        $feature = TrainingProposalFeatureVector::where('job_id', $id)
-            ->findOrFail($id2);
-
-        // Manually optimized query for the cosine distance. The nearestNeighbors()
-        // method of pgvector seems to compute the distances twice and returns lots
-        // of data that we don't need.
-        $ids = $feature->whereNotNull('vector')
-            ->where('id', '!=', $feature->id)
-            ->where('job_id', $id)
-            ->orderByRaw('vector <=> ?', [$feature->vector])
-            ->pluck('id');
-
-        $count = $ids->count();
-        if ($count === 0) {
+        $feature = TrainingProposalFeatureVector::findOrFail($id2);
+        $query = TrainingProposalFeatureVector::where('job_id', $id);
+        $hasFeatures = $query->clone()
+            ->whereNotNull('vector')
+            ->whereNot('id', $id2)
+            ->exists();
+
+        if (!$hasFeatures) {
             abort(Response::HTTP_NOT_FOUND);
         }
 
-        if ($count !== ($job->trainingProposals()->count() - 1)) {
-            // Add IDs of proposals without feature vectors at the end.
-            $ids = $ids->concat(
-                $job->trainingProposals()
-                    ->whereNotIn('id', $ids)
-                    ->whereNot('id', $id2)
-                    ->pluck('id')
-            );
-        }
+        $yieldItems = function () use ($query, $feature, $job): \Generator {
+            // Manually optimized query for the cosine distance. The nearestNeighbors()
+            // method of pgvector seems to compute the distances twice and returns lots
+            // of data that we don't need.
+            $idsQuery = $query->clone()
+                ->whereNotNull('vector')
+                ->whereNot('id', $feature->id)
+                ->orderByRaw('vector <=> ?', [$feature->vector])
+                ->orderBy('id')
+                ->select('id');
+
+            foreach ($idsQuery->lazy() as $item) {
+                yield $item->id;
+            }
+
+            // Add IDs of candidates without feature vectors at the end.
+            $remainingIdsQuery = $job->trainingProposals()
+                ->whereNotIn('id', function ($query) use ($job) {
+                    $query->select('id')
+                        ->from('maia_training_proposal_feature_vectors')
+                        ->where('job_id', $job->id);
+                });
+
+            foreach ($remainingIdsQuery->lazyById() as $item) {
+                yield $item->id;
+            }
+        };
 
-        return $ids;
+        // Use a streamed response because there can be a lot of items.
+        return response()->streamJson($yieldItems());
     }
 
     /**
diff --git a/tests/Http/Controllers/Api/AnnotationCandidateControllerTest.php b/tests/Http/Controllers/Api/AnnotationCandidateControllerTest.php
index 66a648c..5f25cb1 100644
--- a/tests/Http/Controllers/Api/AnnotationCandidateControllerTest.php
+++ b/tests/Http/Controllers/Api/AnnotationCandidateControllerTest.php
@@ -225,9 +225,20 @@ public function testIndexSimilarity()
             'vector' => range(0, 383),
         ]);
 
-        $this->getJson("/api/v1/maia-jobs/{$id}/annotation-candidates/similar-to/{$ac1->id}")
-            ->assertStatus(200)
-            ->assertExactJson([$ac3->id, $ac2->id]);
+        $response = $this->getJson("/api/v1/maia-jobs/{$id}/annotation-candidates/similar-to/{$ac1->id}")
+            ->assertStatus(200);
+
+        ob_start();
+        $response->sendContent();
+        $content = ob_get_clean();
+        $response = new TestResponse(
+            new Response($content,
+                $response->baseResponse->getStatusCode(),
+                $response->baseResponse->headers->all()
+            )
+        );
+
+        $response->assertExactJson([$ac3->id, $ac2->id]);
     }
 
     public function testIndexSimilarityMissing()
@@ -250,9 +261,20 @@ public function testIndexSimilarityMissing()
         $ac3 = AnnotationCandidateTest::create(['job_id' => $id]);
 
         $this->beEditor();
-        $this->getJson("/api/v1/maia-jobs/{$id}/annotation-candidates/similar-to/{$ac1->id}")
-            ->assertStatus(200)
-            ->assertExactJson([$ac2->id, $ac3->id]);
+        $response = $this->getJson("/api/v1/maia-jobs/{$id}/annotation-candidates/similar-to/{$ac1->id}")
+            ->assertStatus(200);
+
+        ob_start();
+        $response->sendContent();
+        $content = ob_get_clean();
+        $response = new TestResponse(
+            new Response($content,
+                $response->baseResponse->getStatusCode(),
+                $response->baseResponse->headers->all()
+            )
+        );
+
+        $response->assertExactJson([$ac2->id, $ac3->id]);
     }
 
     public function testIndexSimilarityEmpty()
diff --git a/tests/Http/Controllers/Api/TrainingProposalControllerTest.php b/tests/Http/Controllers/Api/TrainingProposalControllerTest.php
index c73403f..0bd04ad 100644
--- a/tests/Http/Controllers/Api/TrainingProposalControllerTest.php
+++ b/tests/Http/Controllers/Api/TrainingProposalControllerTest.php
@@ -207,9 +207,20 @@ public function testIndexSimilarity()
             'vector' => range(0, 383),
         ]);
 
-        $this->getJson("/api/v1/maia-jobs/{$id}/training-proposals/similar-to/{$tp1->id}")
-            ->assertStatus(200)
-            ->assertExactJson([$tp3->id, $tp2->id]);
+        $response = $this->getJson("/api/v1/maia-jobs/{$id}/training-proposals/similar-to/{$tp1->id}")
+            ->assertStatus(200);
+
+        ob_start();
+        $response->sendContent();
+        $content = ob_get_clean();
+        $response = new TestResponse(
+            new Response($content,
+                $response->baseResponse->getStatusCode(),
+                $response->baseResponse->headers->all()
+            )
+        );
+
+        $response->assertExactJson([$tp3->id, $tp2->id]);
     }
 
     public function testIndexSimilarityMissing()
@@ -232,9 +243,20 @@ public function testIndexSimilarityMissing()
         $tp3 = TrainingProposalTest::create(['job_id' => $id]);
 
         $this->beEditor();
-        $this->getJson("/api/v1/maia-jobs/{$id}/training-proposals/similar-to/{$tp1->id}")
-            ->assertStatus(200)
-            ->assertExactJson([$tp2->id, $tp3->id]);
+        $response = $this->getJson("/api/v1/maia-jobs/{$id}/training-proposals/similar-to/{$tp1->id}")
+            ->assertStatus(200);
+
+        ob_start();
+        $response->sendContent();
+        $content = ob_get_clean();
+        $response = new TestResponse(
+            new Response($content,
+                $response->baseResponse->getStatusCode(),
+                $response->baseResponse->headers->all()
+            )
+        );
+
+        $response->assertExactJson([$tp2->id, $tp3->id]);
     }
 
     public function testIndexSimilarityEmpty()