From 3b1e8c654c514b406c65fe4f018ebc44829ed33c Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 1 Oct 2026 17:10:41 -0700
Subject: [PATCH 01/24] Update pytest.yml

---
 .github/workflows/pytest.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/pytest.yml b/.github/workflows/pytest.yml
index 319bfea53..cefea6e6f 100644
--- a/.github/workflows/pytest.yml
+++ b/.github/workflows/pytest.yml
@@ -20,7 +20,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ['ubuntu-latest']
-        python-version: ['3.11', '3.12', '3.13', '3.14']
+        python-version: ['3.11', '3.12', '3.13', '3.14', '3.15']
     steps:
       - uses: actions/checkout@v6
       - name: Install uv

From 2c5cb6917f9bc39f314e60b6d18e8e533e3ca80b Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 14:47:27 -0700
Subject: [PATCH 02/24] Update pyproject.toml

---
 pyproject.toml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pyproject.toml b/pyproject.toml
index c71ebea26..42ae46a22 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,6 +26,7 @@ classifiers = [
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.14",
+    "Programming Language :: Python :: 3.15",
 ]
 keywords = ["actuarial", "reserving", "insurance", "chainladder", "IBNR"]
 dependencies = [

From 49e42a83cd3ddd23a1943eb8a72dac274a47534c Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 15:22:08 -0700
Subject: [PATCH 03/24] Update pyproject.toml

---
 pyproject.toml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pyproject.toml b/pyproject.toml
index 42ae46a22..08c3fb944 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -37,6 +37,7 @@ dependencies = [
     "matplotlib",  # Required for TriangleDisplay.heatmap()
     "dill",
     "patsy>=1.0.2",  # 1.0.1 breaks on pandas 3 default str dtype (np.issubdtype on StringDtype)
+    "numba>=0.68.0 ; python_version >= '3.15'",
 ]
 
 [project.urls]

From abd9d54ad6ab1d913a5821d3b736a86f3a0c2b48 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 15:33:16 -0700
Subject: [PATCH 04/24] Update pyproject.toml

---
 pyproject.toml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pyproject.toml b/pyproject.toml
index 08c3fb944..2ab1c67be 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,6 +50,7 @@ Repository = "https://github.com/casact/chainladder-python"
 [project.optional-dependencies]
 dev = [
     "lxml",
+    "lxml>=0.7.0 ; python_version >= '3.15'",
     "pytest",
     "pytest-cov",
     "pytest-xdist",
@@ -77,6 +78,7 @@ docs = [
 ]
 test = [
     "lxml",
+    "lxml>=0.7.0 ; python_version >= '3.15'",
     "nbmake",
     "pytest",
     "jinja2",

From 164e7291bce29773d93583eaf0ffa56c1bef4e3c Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 15:45:53 -0700
Subject: [PATCH 05/24] Update pyproject.toml

---
 pyproject.toml | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 2ab1c67be..f1c576697 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -37,7 +37,7 @@ dependencies = [
     "matplotlib",  # Required for TriangleDisplay.heatmap()
     "dill",
     "patsy>=1.0.2",  # 1.0.1 breaks on pandas 3 default str dtype (np.issubdtype on StringDtype)
-    "numba>=0.68.0 ; python_version >= '3.15'",
+    "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15
 ]
 
 [project.urls]
@@ -49,7 +49,7 @@ Repository = "https://github.com/casact/chainladder-python"
 
 [project.optional-dependencies]
 dev = [
-    "lxml",
+    "lxml ; python_version < '3.15'",
     "lxml>=0.7.0 ; python_version >= '3.15'",
     "pytest",
     "pytest-cov",
@@ -77,7 +77,7 @@ docs = [
     "statsmodels>=0.14.6"  # For docs example; <0.14.6 fails to import under pandas 3
 ]
 test = [
-    "lxml",
+    "lxml ; python_version < '3.15'",
     "lxml>=0.7.0 ; python_version >= '3.15'",
     "nbmake",
     "pytest",

From 3e47b97a76409601ada75ac0c51aaf6cb2e0272e Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 15:58:49 -0700
Subject: [PATCH 06/24] Update pyproject.toml

---
 pyproject.toml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index f1c576697..3c5defa71 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,7 +50,7 @@ Repository = "https://github.com/casact/chainladder-python"
 [project.optional-dependencies]
 dev = [
     "lxml ; python_version < '3.15'",
-    "lxml>=0.7.0 ; python_version >= '3.15'",
+    "lxml>=6.1.3 ; python_version >= '3.15'",
     "pytest",
     "pytest-cov",
     "pytest-xdist",
@@ -78,7 +78,7 @@ docs = [
 ]
 test = [
     "lxml ; python_version < '3.15'",
-    "lxml>=0.7.0 ; python_version >= '3.15'",
+    "lxml>=6.1.3 ; python_version >= '3.15'",
     "nbmake",
     "pytest",
     "jinja2",

From 6eed77c1c1b6ee661a1ea71b0e29880e5ce4b7fd Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 17:05:51 -0700
Subject: [PATCH 07/24] Update pyproject.toml

---
 pyproject.toml | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index 3c5defa71..dbe019c1d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -33,11 +33,13 @@ dependencies = [
     "pandas >=2.3.3, !=3.0.4",
     "scikit-learn>1.4.2",
     "sparse>=0.18",
+    "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15
     "numpy>=2.0",
     "matplotlib",  # Required for TriangleDisplay.heatmap()
+    "contourpy >= 1.4.0 ; python_version >= '3.15'",  # Required for matplotlib
     "dill",
     "patsy>=1.0.2",  # 1.0.1 breaks on pandas 3 default str dtype (np.issubdtype on StringDtype)
-    "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15
+
 ]
 
 [project.urls]

From c0b2e2b694bc264b518b027faca81b8a84f54dd3 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 17:11:24 -0700
Subject: [PATCH 08/24] Update pyproject.toml

---
 pyproject.toml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index dbe019c1d..32fefc492 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -30,7 +30,8 @@ classifiers = [
 ]
 keywords = ["actuarial", "reserving", "insurance", "chainladder", "IBNR"]
 dependencies = [
-    "pandas >=2.3.3, !=3.0.4",
+    "pandas >=2.3.3, !=3.0.4 ; python_version < '3.15'",
+    "pandas >=3.0.6 ; python_version >= '3.15'",
     "scikit-learn>1.4.2",
     "sparse>=0.18",
     "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15

From fd8134d0ea1fb525569f95634baa29ba2d4f9690 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 17:17:52 -0700
Subject: [PATCH 09/24] Update pyproject.toml

---
 pyproject.toml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 32fefc492..895ff61eb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -36,8 +36,8 @@ dependencies = [
     "sparse>=0.18",
     "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15
     "numpy>=2.0",
-    "matplotlib",  # Required for TriangleDisplay.heatmap()
-    "contourpy >= 1.4.0 ; python_version >= '3.15'",  # Required for matplotlib
+    "matplotlib>=3.11.2",  # Required for TriangleDisplay.heatmap()
+    "contourpy>=1.4.0 ; python_version >= '3.15'",  # Required for matplotlib
     "dill",
     "patsy>=1.0.2",  # 1.0.1 breaks on pandas 3 default str dtype (np.issubdtype on StringDtype)
 

From 07946020dfaa97754f5e5fb08c5fe12e88f9f550 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 17:29:02 -0700
Subject: [PATCH 10/24] Update pyproject.toml

---
 pyproject.toml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index 895ff61eb..24ef54fab 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -70,7 +70,8 @@ docs = [
     "sphinx-rtd-theme",
     "nbsphinx",
     "numpydoc",
-    "jupyter-book<2.0",  # Pin to v1.x - v2 doesn't support autodoc/autosummary yet
+    "jupyter-book<2.0 ; python_version < '3.15'",  # Pin to v1.x - v2 doesn't support autodoc/autosummary yet
+    "jupyter-book>=2.0 ; python_version >= '3.15'",
     "sphinx-book-theme>=1.1.4,<1.2; python_version < '3.11'",
     "sphinx-book-theme>=1.2,<1.3; python_version >= '3.11'",
     "sphinx-togglebutton",

From e3a197854d5f5d76920a74e1577eab9392842473 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 17:33:05 -0700
Subject: [PATCH 11/24] Update pyproject.toml

---
 pyproject.toml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index 24ef54fab..aeaa56374 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,7 +35,8 @@ dependencies = [
     "scikit-learn>1.4.2",
     "sparse>=0.18",
     "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15
-    "numpy>=2.0",
+    "numpy>=2.0 ; python_version < '3.15'",
+    "numpy>=2.5.2 ; python_version >= '3.15'",
     "matplotlib>=3.11.2",  # Required for TriangleDisplay.heatmap()
     "contourpy>=1.4.0 ; python_version >= '3.15'",  # Required for matplotlib
     "dill",

From 67cfcfeae7210bba289c32144551d8a66e385eef Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 20:58:01 -0700
Subject: [PATCH 12/24] Update pyproject.toml

---
 pyproject.toml | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index aeaa56374..97381cb30 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -71,8 +71,8 @@ docs = [
     "sphinx-rtd-theme",
     "nbsphinx",
     "numpydoc",
-    "jupyter-book<2.0 ; python_version < '3.15'",  # Pin to v1.x - v2 doesn't support autodoc/autosummary yet
-    "jupyter-book>=2.0 ; python_version >= '3.15'",
+    "jupyter-book<2.0",  # Pin to v1.x - v2 doesn't support autodoc/autosummary yet
+    "rpds-py>=2026.5.1 ; python_version >= '3.15'",  # needed by jupyter-book
     "sphinx-book-theme>=1.1.4,<1.2; python_version < '3.11'",
     "sphinx-book-theme>=1.2,<1.3; python_version >= '3.11'",
     "sphinx-togglebutton",
@@ -85,6 +85,7 @@ test = [
     "lxml ; python_version < '3.15'",
     "lxml>=6.1.3 ; python_version >= '3.15'",
     "nbmake",
+    "rpds-py>=2026.5.1 ; python_version >= '3.15'",  # needed by nbmake
     "pytest",
     "jinja2",
     "ipython",

From 42661fdbfd21e6cb3014ede6835a3e84115cac31 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 20:59:48 -0700
Subject: [PATCH 13/24] Update pyproject.toml

---
 pyproject.toml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index 97381cb30..8e167534c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,7 +32,8 @@ keywords = ["actuarial", "reserving", "insurance", "chainladder", "IBNR"]
 dependencies = [
     "pandas >=2.3.3, !=3.0.4 ; python_version < '3.15'",
     "pandas >=3.0.6 ; python_version >= '3.15'",
-    "scikit-learn>1.4.2",
+    "scikit-learn>1.4.2 ; python_version < '3.15'",
+    "scikit-learn>=1.9.1 ; python_version >= '3.15'",
     "sparse>=0.18",
     "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15
     "numpy>=2.0 ; python_version < '3.15'",

From 67df4b842ba39d7690a166f86dc5986ccd4288e0 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 21:09:50 -0700
Subject: [PATCH 14/24] Update pyproject.toml

---
 pyproject.toml | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 8e167534c..dfa4d13f6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -80,7 +80,8 @@ docs = [
     "ipython",
     "parso>=0.8",
     "polars",  # For docs examples
-    "statsmodels>=0.14.6"  # For docs example; <0.14.6 fails to import under pandas 3
+    "statsmodels>=0.14.6 ; python_version < '3.15'"  # For docs example; <0.14.6 fails to import under pandas 3
+    "statsmodels>=0.15.0 ; python_version >= '3.15'"  # For docs example; <0.14.6 fails to import under pandas 3
 ]
 test = [
     "lxml ; python_version < '3.15'",
@@ -94,7 +95,8 @@ test = [
     "polars",
     "pyarrow",
     "dask",
-    'statsmodels>=0.14.6'
+    "statsmodels>=0.14.6 ; python_version < '3.15'"
+    "statsmodels>=0.15.0 ; python_version >= '3.15'"
 ]
 performance = [
     "dask",  # For distributed computing

From cf041c3f5fbe2cc936c89f814ba86a2ad60eba12 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 21:12:40 -0700
Subject: [PATCH 15/24] Update pyproject.toml

---
 pyproject.toml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index dfa4d13f6..da88adda8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -80,7 +80,7 @@ docs = [
     "ipython",
     "parso>=0.8",
     "polars",  # For docs examples
-    "statsmodels>=0.14.6 ; python_version < '3.15'"  # For docs example; <0.14.6 fails to import under pandas 3
+    "statsmodels>=0.14.6 ; python_version < '3.15'",  # For docs example; <0.14.6 fails to import under pandas 3
     "statsmodels>=0.15.0 ; python_version >= '3.15'"  # For docs example; <0.14.6 fails to import under pandas 3
 ]
 test = [
@@ -95,7 +95,7 @@ test = [
     "polars",
     "pyarrow",
     "dask",
-    "statsmodels>=0.14.6 ; python_version < '3.15'"
+    "statsmodels>=0.14.6 ; python_version < '3.15'".
     "statsmodels>=0.15.0 ; python_version >= '3.15'"
 ]
 performance = [

From e6f9e33deee6b1322fe2d6ba33c60ad7a30e6a7f Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 21:13:04 -0700
Subject: [PATCH 16/24] Update pyproject.toml

---
 pyproject.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index da88adda8..2f992d154 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -95,7 +95,7 @@ test = [
     "polars",
     "pyarrow",
     "dask",
-    "statsmodels>=0.14.6 ; python_version < '3.15'".
+    "statsmodels>=0.14.6 ; python_version < '3.15'",
     "statsmodels>=0.15.0 ; python_version >= '3.15'"
 ]
 performance = [

From 4b632554c4f80668e01521af732f2c63ed934520 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 21:31:46 -0700
Subject: [PATCH 17/24] Update pyproject.toml

---
 pyproject.toml | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 2f992d154..a7d69367c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -80,8 +80,8 @@ docs = [
     "ipython",
     "parso>=0.8",
     "polars",  # For docs examples
-    "statsmodels>=0.14.6 ; python_version < '3.15'",  # For docs example; <0.14.6 fails to import under pandas 3
-    "statsmodels>=0.15.0 ; python_version >= '3.15'"  # For docs example; <0.14.6 fails to import under pandas 3
+    "statsmodels>=0.14.6",  # For docs example; <0.14.6 fails to import under pandas 3
+    "scipy>=0.18.1 ; python_version >= '3.15'"
 ]
 test = [
     "lxml ; python_version < '3.15'",
@@ -95,8 +95,8 @@ test = [
     "polars",
     "pyarrow",
     "dask",
-    "statsmodels>=0.14.6 ; python_version < '3.15'",
-    "statsmodels>=0.15.0 ; python_version >= '3.15'"
+    "statsmodels>=0.14.6",
+    "scipy>=0.18.1 ; python_version >= '3.15'"
 ]
 performance = [
     "dask",  # For distributed computing

From 98f4fb0af2f3d58fe36747442fab5c0e5165a4c2 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 21:34:44 -0700
Subject: [PATCH 18/24] Update pyproject.toml

---
 pyproject.toml | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index a7d69367c..2168815e2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -80,8 +80,8 @@ docs = [
     "ipython",
     "parso>=0.8",
     "polars",  # For docs examples
-    "statsmodels>=0.14.6",  # For docs example; <0.14.6 fails to import under pandas 3
-    "scipy>=0.18.1 ; python_version >= '3.15'"
+    "scipy>=0.18.1 ; python_version >= '3.15'",
+    "statsmodels>=0.14.6"  # For docs example; <0.14.6 fails to import under pandas 3
 ]
 test = [
     "lxml ; python_version < '3.15'",
@@ -95,8 +95,8 @@ test = [
     "polars",
     "pyarrow",
     "dask",
-    "statsmodels>=0.14.6",
-    "scipy>=0.18.1 ; python_version >= '3.15'"
+    "scipy>=0.18.1 ; python_version >= '3.15'",
+    "statsmodels>=0.14.6"
 ]
 performance = [
     "dask",  # For distributed computing

From 202ae71cd15cbcff80900a5c4dc5e99f60be1b77 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 22:10:26 -0700
Subject: [PATCH 19/24] Update pyproject.toml

---
 pyproject.toml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 2168815e2..38f7c67c6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -80,7 +80,7 @@ docs = [
     "ipython",
     "parso>=0.8",
     "polars",  # For docs examples
-    "scipy>=0.18.1 ; python_version >= '3.15'",
+    "scipy>=1.18.1 ; python_version >= '3.15'",
     "statsmodels>=0.14.6"  # For docs example; <0.14.6 fails to import under pandas 3
 ]
 test = [
@@ -95,7 +95,7 @@ test = [
     "polars",
     "pyarrow",
     "dask",
-    "scipy>=0.18.1 ; python_version >= '3.15'",
+    "scipy>=1.18.1 ; python_version >= '3.15'",
     "statsmodels>=0.14.6"
 ]
 performance = [

From 2ec10eef5eb01c7a961af8f461ff453829ca9c23 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 22:14:45 -0700
Subject: [PATCH 20/24] Update pyproject.toml

---
 pyproject.toml | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index 38f7c67c6..f3ad70c7d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -93,7 +93,6 @@ test = [
     "ipython",
     "pytest-cov",  # For coverage testing
     "polars",
-    "pyarrow",
     "dask",
     "scipy>=1.18.1 ; python_version >= '3.15'",
     "statsmodels>=0.14.6"

From 003ac1048c1e3d123f21ed0bfe8d7edabad5a852 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Thu, 8 Oct 2026 22:23:07 -0700
Subject: [PATCH 21/24] Update pyproject.toml

---
 pyproject.toml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pyproject.toml b/pyproject.toml
index f3ad70c7d..2d2158427 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -93,6 +93,8 @@ test = [
     "ipython",
     "pytest-cov",  # For coverage testing
     "polars",
+    "pyarrow ; python_version < '3.15'",
+    "pyarrow>=26.0.0 ; python_version >= '3.15'",
     "dask",
     "scipy>=1.18.1 ; python_version >= '3.15'",
     "statsmodels>=0.14.6"

From 0eaea9b65c3c73d52a45b2674ab802d3fea29717 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Fri, 9 Oct 2026 23:37:55 -0700
Subject: [PATCH 22/24] Update base.py

---
 chainladder/core/base.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/chainladder/core/base.py b/chainladder/core/base.py
index ac89fc131..adf91389c 100644
--- a/chainladder/core/base.py
+++ b/chainladder/core/base.py
@@ -699,7 +699,9 @@ def valuation(self):
         val_array = val_array[:, None]
         s = slice(None, -1) if ddims[-1] == 9999 else slice(None, None)
         val_array = (
-            val_array.astype("datetime64[M]") + ddim_arr[s][None, :] + 1
+            val_array.astype("datetime64[M]")
+            + ddim_arr[s][None, :].astype("timedelta64[M]")
+            + np.timedelta64(1, "M")
         ).astype(__dt64_dtype__) - np.timedelta64(1, __dt64_unit__)
         if ddims[-1] == 9999:
             ult = np.repeat(np.datetime64(options.ULT_VAL), val_array.shape[0])[:, None]

From 00a7053bb7a981ded73c47f64998942adc859091 Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Fri, 9 Oct 2026 23:55:57 -0700
Subject: [PATCH 23/24] Update pyproject.toml

---
 pyproject.toml | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 2d2158427..bb2f195c2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,17 +32,17 @@ keywords = ["actuarial", "reserving", "insurance", "chainladder", "IBNR"]
 dependencies = [
     "pandas >=2.3.3, !=3.0.4 ; python_version < '3.15'",
     "pandas >=3.0.6 ; python_version >= '3.15'",
-    "scikit-learn>1.4.2 ; python_version < '3.15'",
+    "scikit-learn>1.7.0 ; python_version < '3.15'",
     "scikit-learn>=1.9.1 ; python_version >= '3.15'",
     "sparse>=0.18",
     "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15
-    "numpy>=2.0 ; python_version < '3.15'",
+    "numpy>=2.3 ; python_version < '3.15'",
     "numpy>=2.5.2 ; python_version >= '3.15'",
-    "matplotlib>=3.11.2",  # Required for TriangleDisplay.heatmap()
+    "matplotlib ; python_version < '3.15'",  # Required for TriangleDisplay.heatmap()
+    "matplotlib>=3.11.2 ; python_version >= '3.15'",
     "contourpy>=1.4.0 ; python_version >= '3.15'",  # Required for matplotlib
     "dill",
     "patsy>=1.0.2",  # 1.0.1 breaks on pandas 3 default str dtype (np.issubdtype on StringDtype)
-
 ]
 
 [project.urls]
@@ -81,7 +81,7 @@ docs = [
     "parso>=0.8",
     "polars",  # For docs examples
     "scipy>=1.18.1 ; python_version >= '3.15'",
-    "statsmodels>=0.14.6"  # For docs example; <0.14.6 fails to import under pandas 3
+    "statsmodels>=0.14.6",  # For docs example; <0.14.6 fails to import under pandas 3
 ]
 test = [
     "lxml ; python_version < '3.15'",
@@ -97,7 +97,7 @@ test = [
     "pyarrow>=26.0.0 ; python_version >= '3.15'",
     "dask",
     "scipy>=1.18.1 ; python_version >= '3.15'",
-    "statsmodels>=0.14.6"
+    "statsmodels>=0.14.6",
 ]
 performance = [
     "dask",  # For distributed computing

From 1f6823ce408fe45caf6901e406aa358655d219dc Mon Sep 17 00:00:00 2001
From: henrydingliu <106109320+henrydingliu@users.noreply.github.com>
Date: Sat, 10 Oct 2026 00:02:32 -0700
Subject: [PATCH 24/24] Update pyproject.toml

---
 pyproject.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index bb2f195c2..fcc67a87b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,7 +32,7 @@ keywords = ["actuarial", "reserving", "insurance", "chainladder", "IBNR"]
 dependencies = [
     "pandas >=2.3.3, !=3.0.4 ; python_version < '3.15'",
     "pandas >=3.0.6 ; python_version >= '3.15'",
-    "scikit-learn>1.7.0 ; python_version < '3.15'",
+    "scikit-learn>=1.7.0 ; python_version < '3.15'",
     "scikit-learn>=1.9.1 ; python_version >= '3.15'",
     "sparse>=0.18",
     "numba>=0.68.0 ; python_version >= '3.15'",  # numba is needed for sparse. however, sparse does not have a version that officially support python 3.15