diff --git a/CHANGELOG.md b/CHANGELOG.md
index 077e103..d84758b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,16 +8,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
-
 - `TokenChunker` for token-level chunking using tiktoken with a new `[tokens]` optional extra (closes #44)
-
 - Structured logging for ingest, query, and retriever stages, including timing and empty-ingest warnings (closes #41).
 - `RecursiveChunker.from_config()` for creating a chunker from pipeline configuration (closes #25).
 
 ### Fixed
+- Optimize `InMemoryRetriever.add()` to normalize only newly added vectors and avoid rebuilding the full matrix on every call (closes #27).
 - `TextFileLoader` and `MarkdownLoader` now convert Unicode decoding and unknown encoding errors to `LoaderError`, with configurable text decoding error handling (closes #24).
 - Validate chunker size and overlap parameters in `FixedSizeChunker` and `SentenceChunker` (closes #25).
 
+
 ## [0.3.0] - 2026-09-25
 
 ### Added
@@ -37,6 +37,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Enforce LF line endings with `.gitattributes` across platforms while keeping PNG files binary (closes #48).
 - `InMemoryRetriever.retrieve()` now returns an empty list for non-positive `top_k` values and raises `RetrieverError` for non-integer or boolean `top_k` values (closes #23).
 - `InMemoryRetriever` now raises `RetrieverError` for invalid vectors and dimension mismatches, validates complete batches before updating stored data, and treats empty batches as a no-op. Vector validation and normalization are shared with `FAISSRetriever` (closes #26).
+### Fixed
+- Optimize `InMemoryRetriever.add()` to normalize only newly added vectors and avoid rebuilding the full matrix on every call (closes #27).
 
 ## [0.2.0] - 2026-09-19
 
diff --git a/ragframework/retriever/in_memory.py b/ragframework/retriever/in_memory.py
index 104b38e..0d37340 100644
--- a/ragframework/retriever/in_memory.py
+++ b/ragframework/retriever/in_memory.py
@@ -25,6 +25,7 @@ class InMemoryRetriever(Retriever):
     def __init__(self) -> None:
         self._chunks: list[Chunk] = []
         self._matrix: np.ndarray[Any, Any] | None = None  # shape (N, dim)
+        self._matrix_blocks: list[np.ndarray[Any, Any]] = []
         self._dimension: int | None = None
 
     def add(self, chunks: list[Chunk]) -> None:
@@ -55,10 +56,9 @@ def add(self, chunks: list[Chunk]) -> None:
             vectors.append(vector)
 
         matrix = np.stack(vectors)
-        if self._matrix is not None:
-            matrix = np.concatenate((self._matrix, matrix))
+        self._matrix_blocks.append(matrix)
 
-        self._matrix = matrix
+        self._matrix = None
         self._dimension = expected_dimension
         self._chunks.extend(chunks)
         logger.debug(
@@ -77,13 +77,23 @@ def retrieve(self, query_embedding: list[float], top_k: int = 5) -> list[Chunk]:
         """
         if not isinstance(top_k, int) or isinstance(top_k, bool):
             raise RetrieverError("top_k must be an integer.")
-        if top_k <= 0 or not self._chunks or self._matrix is None:
+        if top_k <= 0 or not self._chunks:
             return []
         q = validate_vector(query_embedding, "Query embedding")
         if q.shape[0] != self._dimension:
             raise RetrieverError(
                 f"Query embedding has dimension {q.shape[0]}; expected {self._dimension}."
             )
+        if self._matrix is None:
+            if len(self._matrix_blocks) == 1:
+                # Reuse the existing array; do not create another copy.
+                self._matrix = self._matrix_blocks[0]
+            else:
+                # Consolidate all blocks into one cached matrix and replace the
+                # old block references so the original arrays can be released.
+                self._matrix = np.concatenate(self._matrix_blocks)
+                self._matrix_blocks = [self._matrix]
+
         scores: np.ndarray[Any, Any] = self._matrix @ q
         k = min(top_k, len(self._chunks))
         top_indices = np.argpartition(scores, -k)[-k:]
diff --git a/tests/test_document/test_chunkers.py b/tests/test_document/test_chunkers.py
index bc0ad00..1835688 100644
--- a/tests/test_document/test_chunkers.py
+++ b/tests/test_document/test_chunkers.py
@@ -3,6 +3,7 @@
 import builtins
 import sys
 import types
+from typing import Any
 
 import pytest
 
@@ -12,7 +13,6 @@
     RecursiveChunker,
     SentenceChunker,
 )
-from typing import Any
 
 
 def test_recursive_chunker_from_config():
diff --git a/tests/test_retriever/test_in_memory.py b/tests/test_retriever/test_in_memory.py
index 88fb664..86204e5 100644
--- a/tests/test_retriever/test_in_memory.py
+++ b/tests/test_retriever/test_in_memory.py
@@ -172,3 +172,75 @@ def test_bool_top_k_raises_retriever_error(self):
 
         with pytest.raises(RetrieverError, match="top_k must be an integer"):
             r.retrieve([1.0, 0.0], top_k=True)
+
+    def test_batched_add_matches_single_batch(self):
+        chunks = [
+            make_chunk("a", [1.0, 0.0]),
+            make_chunk("b", [0.0, 1.0]),
+            make_chunk("c", [1.0, 1.0]),
+            make_chunk("d", [-1.0, 0.0]),
+        ]
+
+        single_batch = InMemoryRetriever()
+        single_batch.add(chunks)
+
+        batched = InMemoryRetriever()
+        batched.add(chunks[:2])
+        batched.add(chunks[2:])
+
+        query = [1.0, 1.0]
+
+        single_results = single_batch.retrieve(query, top_k=4)
+        batched_results = batched.retrieve(query, top_k=4)
+
+        assert len(batched_results) == len(single_results)
+        assert batched_results[0].id == single_results[0].id
+
+def test_retrieve_consolidates_matrix_blocks_without_duplicate_storage():
+    retriever = InMemoryRetriever()
+
+    chunks = [
+        make_chunk("a", [1.0, 0.0]),
+        make_chunk("b", [0.0, 1.0]),
+        make_chunk("c", [1.0, 1.0]),
+    ]
+
+    retriever.add(chunks[:1])
+    retriever.add(chunks[1:])
+
+    assert len(retriever._matrix_blocks) == 2
+    assert retriever._matrix is None
+
+    retriever.retrieve([1.0, 1.0], top_k=3)
+
+    assert retriever._matrix is not None
+    assert len(retriever._matrix_blocks) == 1
+    assert retriever._matrix_blocks[0] is retriever._matrix
+
+def test_add_after_consolidation_preserves_all_results():
+    retriever = InMemoryRetriever()
+
+    first = [
+        make_chunk("a", [1.0, 0.0]),
+        make_chunk("b", [0.0, 1.0]),
+    ]
+    second = [
+        make_chunk("c", [1.0, 1.0]),
+    ]
+
+    retriever.add(first)
+    retriever.retrieve([1.0, 1.0], top_k=2)
+
+    assert len(retriever._matrix_blocks) == 1
+    assert retriever._matrix_blocks[0] is retriever._matrix
+
+    retriever.add(second)
+
+    assert retriever._matrix is None
+    assert len(retriever._matrix_blocks) == 2
+
+    results = retriever.retrieve([1.0, 1.0], top_k=3)
+
+    assert [chunk.id for chunk in results] == ["c", "b", "a"]
+    assert len(retriever._matrix_blocks) == 1
+    assert retriever._matrix_blocks[0] is retriever._matrix