diff --git a/benchmarks/bench_scaling.py b/benchmarks/bench_scaling.py
new file mode 100644
index 0000000..5b395a8
--- /dev/null
+++ b/benchmarks/bench_scaling.py
@@ -0,0 +1,59 @@
+"""Benchmark how training scales with text size and merge count."""
+
+import time
+
+from complex_tokenization.fast_bpe_trainer import FastBPETrainer
+from complex_tokenization.graphs.settings import GraphSettings
+from complex_tokenization.graphs.units import utf8_clusters
+from complex_tokenization.graphs.words import words
+from complex_tokenization.trainer import Trainer
+
+
+def train_graph_bpe(texts, num_merges):
+    GraphSettings.ONLY_MINIMAL_MERGES = True
+    GraphSettings.MAX_MERGE_SIZE = 2
+    GraphSettings.USE_SINGLETONS = False
+    graphs = tuple(words(t, connected=False, units=utf8_clusters) for t in texts)
+    trainer = Trainer(graphs=graphs)
+    trainer.train(num_merges=num_merges)
+    return trainer.get_merges()
+
+
+def train_fast_bpe(texts, num_merges):
+    fast = FastBPETrainer(texts)
+    fast.train(num_merges=num_merges)
+    return fast.get_merges()
+
+
+BASE_TEXT = "the teacher teaches the thick thing about the theorem "
+
+
+def run():
+    print(f"\n{'='*80}")
+    print("Scaling Benchmark: Graph BPE vs Fast BPE")
+    print(f"{'='*80}")
+    print(f"{'Config':30s}  {'Graph BPE':>10s}  {'Fast BPE':>10s}  {'Speedup':>8s}")
+    print("-" * 80)
+
+    for num_texts in [10, 50, 100]:
+        for repeat in [10, 50]:
+            for num_merges in [50, 100, 200]:
+                texts = [BASE_TEXT * repeat] * num_texts
+                total_chars = sum(len(t) for t in texts)
+
+                start = time.perf_counter()
+                graph_merges = train_graph_bpe(texts, num_merges)
+                graph_time = time.perf_counter() - start
+
+                start = time.perf_counter()
+                fast_merges = train_fast_bpe(texts, num_merges)
+                fast_time = time.perf_counter() - start
+
+                speedup = graph_time / fast_time if fast_time > 0 else float('inf')
+                match = "ok" if graph_merges == fast_merges else "MISMATCH"
+                label = f"{num_texts}x{repeat}rep m={num_merges} ({total_chars:,}ch)"
+                print(f"{label:30s}  {graph_time:>9.3f}s  {fast_time:>9.3f}s  {speedup:>7.1f}x  {match}")
+
+
+if __name__ == "__main__":
+    run()
diff --git a/tests/test_scaling.py b/tests/test_scaling.py
new file mode 100644
index 0000000..f594f81
--- /dev/null
+++ b/tests/test_scaling.py
@@ -0,0 +1,27 @@
+"""Test that FastBPE scales well with larger inputs."""
+
+import time
+
+from complex_tokenization.fast_bpe_trainer import FastBPETrainer
+
+BASE = "the teacher teaches the thick thing about the theorem "
+
+
+class TestScaling:
+    def test_100k_chars_under_5s(self):
+        texts = [BASE * 50] * 100  # ~270k chars
+        start = time.perf_counter()
+        fast = FastBPETrainer(texts)
+        fast.train(num_merges=25)
+        elapsed = time.perf_counter() - start
+        assert elapsed < 5, f"FastBPE on 270k chars took {elapsed:.1f}s (limit: 5s)"
+        assert len(fast.merges) == 25
+
+    def test_merges_scale_with_data(self):
+        small = [BASE * 10] * 10
+        large = [BASE * 50] * 50
+        f_small = FastBPETrainer(small)
+        f_small.train(num_merges=50)
+        f_large = FastBPETrainer(large)
+        f_large.train(num_merges=50)
+        assert f_small.get_merges() == f_large.get_merges()