diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index f134759d9..c9d385318 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -55,7 +55,7 @@ jobs:
 
         # if changing the below change the run-integration-tests versions and the check-deploy versions
         # Make sure that we are running the integration tests on the first and last versions of the matrix
-        python: ['3.11', '3.12', '3.13', '3.14']
+        python: ['3.11', '3.12', '3.13', '3.14', '3.15']
 
     runs-on: ${{ matrix.os }}
 
@@ -109,7 +109,7 @@ jobs:
           pytest -sv --cov-append --cov=. --cov-report xml tests/unit
       - name: Check for Secret availability
         id: secret-check
-        if: ${{ contains(fromJSON('["3.11"]'), matrix.python) || contains(fromJSON('["3.14"]'), matrix.python) }}
+        if: ${{ contains(fromJSON('["3.11"]'), matrix.python) || contains(fromJSON('["3.15"]'), matrix.python) }}
         # perform secret check & put boolean result as an output
         shell: bash
         run: |
@@ -126,7 +126,7 @@ jobs:
           fi
 
       - name: Download Failed Tests from Previous Attempt
-        if: ${{ github.run_attempt > 1 && (contains(fromJSON('["3.11"]'), matrix.python) || contains(fromJSON('["3.14"]'), matrix.python)) && steps.secret-check.outputs.secrets_available == 'true'}}
+        if: ${{ github.run_attempt > 1 && (contains(fromJSON('["3.11"]'), matrix.python) || contains(fromJSON('["3.15"]'), matrix.python)) && steps.secret-check.outputs.secrets_available == 'true'}}
         uses: actions/download-artifact@v4
         with:
           name: failed-tests-${{ matrix.os }}-${{ matrix.python }}
@@ -142,25 +142,25 @@ jobs:
         shell: bash
 
         # keep versions consistent with the first and last from the strategy matrix
-        if: ${{ (contains(fromJSON('["3.11"]'), matrix.python) || contains(fromJSON('["3.14"]'), matrix.python)) && steps.secret-check.outputs.secrets_available == 'true' && github.event_name != 'release'}}
+        if: ${{ (contains(fromJSON('["3.11"]'), matrix.python) || contains(fromJSON('["3.15"]'), matrix.python)) && steps.secret-check.outputs.secrets_available == 'true' && github.event_name != 'release'}}
         run: |
           # Set SYNAPSE_PROFILE based on OS and Python version
           if [ "${{ startsWith(matrix.os, 'ubuntu') }}" == "true" ]; then
             if [ "${{ matrix.python }}" == "3.11" ]; then
               export SYNAPSE_PROFILE="TestUbuntuMinimumPython"
-            elif [ "${{ matrix.python }}" == "3.14" ]; then
+            elif [ "${{ matrix.python }}" == "3.15" ]; then
               export SYNAPSE_PROFILE="TestUbuntuMaximumPython"
             fi
           elif [ "${{ startsWith(matrix.os, 'windows') }}" == "true" ]; then
             if [ "${{ matrix.python }}" == "3.11" ]; then
               export SYNAPSE_PROFILE="TestWindowsMinimumPython"
-            elif [ "${{ matrix.python }}" == "3.14" ]; then
+            elif [ "${{ matrix.python }}" == "3.15" ]; then
               export SYNAPSE_PROFILE="TestWindowsMaximumPython"
             fi
           elif [ "${{ startsWith(matrix.os, 'macos') }}" == "true" ]; then
             if [ "${{ matrix.python }}" == "3.11" ]; then
               export SYNAPSE_PROFILE="TestMacosMinimumPython"
-            elif [ "${{ matrix.python }}" == "3.14" ]; then
+            elif [ "${{ matrix.python }}" == "3.15" ]; then
               export SYNAPSE_PROFILE="TestMacosMaximumPython"
             fi
           fi
@@ -547,7 +547,7 @@ jobs:
         os: [ubuntu-24.04, macos-15-intel, windows-2022]
 
         # python versions should be consistent with the strategy matrix and the runs-integration-tests versions
-        python: ['3.11', '3.12', '3.13', '3.14']
+        python: ['3.11', '3.12', '3.13', '3.14', '3.15']
 
     runs-on: ${{ matrix.os }}
 
diff --git a/.github/workflows/validate-release.yml b/.github/workflows/validate-release.yml
index 04f4492d2..2d6bc1a31 100644
--- a/.github/workflows/validate-release.yml
+++ b/.github/workflows/validate-release.yml
@@ -16,7 +16,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.14'
+          python-version: '3.15'
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
diff --git a/CLAUDE.md b/CLAUDE.md
index a19452b19..4b1560669 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -6,7 +6,7 @@ Synapse Python Client — official Python SDK and CLI for Synapse (synapse.org),
 
 ## Stack
 
-- Python 3.11–3.14 (`setup.cfg`: `python_requires = >=3.11, <3.15`)
+- Python 3.11–3.15 (`setup.cfg`: `python_requires = >=3.11, <3.16`)
 - HTTP: httpx (async), requests (sync/legacy)
 - Models: stdlib dataclasses (NOT Pydantic)
 - pandas (optional): `pandas>=1.5,<4.0` (`setup.cfg`, 4 places)
@@ -132,7 +132,7 @@ Code must work on every pandas version from 1.5 to 3.x. Use one code path that w
 - Integration tests use `--reruns 3` for flaky retries and `-n 4 --dist loadscope` for parallelism
 - Integration fixtures create per-worker Synapse projects; use `schedule_for_cleanup()` for teardown
 - Auth env vars: `SYNAPSE_AUTH_TOKEN` (bearer token), `SYNAPSE_PROFILE` (config file profile, default: `"default"`), `SYNAPSE_TOKEN_AWS_SSM_PARAMETER_NAME` (AWS SSM path)
-- CI runs integration tests only on Python 3.11 and 3.14 (oldest + newest) to limit Synapse server load
+- CI runs integration tests only on Python 3.11 and 3.15 (oldest + newest) to limit Synapse server load
 - CI job `test-pandas-versions` (`.github/workflows/build.yml`) runs the unit tests on older pandas versions: 1.5.3 on Python 3.11, 2.1.4 on Python 3.12, 2.2.3 on Python 3.13 (ubuntu only). The `package` job needs it. pandas < 2.2.2 requires `numpy<2`, so each matrix entry pins its own numpy version (1.26.4, 1.26.4, 2.5.4).
 
 ## Maintenance
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 06ecb2736..a16981469 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -93,7 +93,7 @@ copied to forks).
 #### Installing the Python Client in a virtual environment with pipenv
 Perform the following one-time steps to set up your local environment.
 
-1. This package uses Python, if you have not already, please install [pyenv](https://github.com/pyenv/pyenv#installation) to manage your Python versions. Versions supported by this package are all versions >=3.11 and <=3.14. If you do not install `pyenv` make sure that Python and `pip` are installed correctly and have been added to your PATH by running `python3 --version` and `pip3 --version`. If your installation was successful, your terminal will return the versions of Python and `pip` that you installed.  **Note**: If you have `pyenv` it will install a specific version of Python for you.
+1. This package uses Python, if you have not already, please install [pyenv](https://github.com/pyenv/pyenv#installation) to manage your Python versions. Versions supported by this package are all versions >=3.11 and <=3.15. If you do not install `pyenv` make sure that Python and `pip` are installed correctly and have been added to your PATH by running `python3 --version` and `pip3 --version`. If your installation was successful, your terminal will return the versions of Python and `pip` that you installed.  **Note**: If you have `pyenv` it will install a specific version of Python for you.
 
 2. Install `pipenv` by running `pip install pipenv`.
     - If you already have `pipenv` installed, ensure that the version is >=2023.9.8 to avoid compatibility issues.
@@ -271,18 +271,18 @@ When adding support for a new Python version or dropping support for an old vers
 
 #### Adding a new Python version
 
-When adding support for a new Python version (e.g., adding Python 3.15), update the following:
+When adding support for a new Python version (e.g., adding Python 3.16), update the following:
 
 **Code configuration files:**
 1. **`setup.cfg`**:
-   - Add the new version to the `classifiers` list under `[metadata]` (e.g., `Programming Language :: Python :: 3.15`)
-   - Update the `python_requires` constraint under `[options]` to include the new version (e.g., `>=3.11, <3.16`)
+   - Add the new version to the `classifiers` list under `[metadata]` (e.g., `Programming Language :: Python :: 3.16`)
+   - Update the `python_requires` constraint under `[options]` to include the new version (e.g., `>=3.11, <3.17`)
 
 2. **`pyproject.toml`**:
    - Update the `target-version` list in the `[tool.black]` section to include the new version if needed
 
 3. **`Dockerfile`**:
-   - Update the base image to use the new Python version (e.g., `FROM python:3.15-slim`)
+   - Update the base image to use the new Python version (e.g., `FROM python:3.16-slim`)
 
 **CI/CD configuration files:**
 1. **`.github/workflows/build.yml`**:
@@ -301,7 +301,7 @@ When dropping support for an old Python version (e.g., removing Python 3.11), up
 **Code configuration files:**
 1. **`setup.cfg`**:
    - Remove the old version from the `classifiers` list under `[metadata]`
-   - Update the `python_requires` constraint under `[options]` to reflect the new minimum version (e.g., `>=3.12, <3.15`)
+   - Update the `python_requires` constraint under `[options]` to reflect the new minimum version (e.g., `>=3.12, <3.16`)
 
 2. **`pyproject.toml`**:
    - Update the `target-version` list in the `[tool.black]` section to remove the old version
diff --git a/Dockerfile b/Dockerfile
index 99b8ffdaa..19d51d148 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM python:3.14-slim
+FROM python:3.15-slim
 RUN echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selections
 
 RUN apt-get update \
diff --git a/README.md b/README.md
index de9d91023..443392b97 100644
--- a/README.md
+++ b/README.md
@@ -78,7 +78,7 @@ flowchart TD
 Installation
 ------------
 
-We test the client on Python 3.11, 3.12, 3.13, and 3.14. It runs on Mac OS X, Linux, and Windows.
+We test the client on Python 3.11, 3.12, 3.13, 3.14, and 3.15. It runs on Mac OS X, Linux, and Windows.
 
 **Version 3.0 and later needs Python 3.10 or higher. Version 4.15.0 and later needs Python 3.11 or higher.**
 
diff --git a/docs/tutorials/installation.md b/docs/tutorials/installation.md
index ca4f2e932..2581f9978 100644
--- a/docs/tutorials/installation.md
+++ b/docs/tutorials/installation.md
@@ -21,7 +21,7 @@ The [synapseclient](https://pypi.python.org/pypi/synapseclient/) package is avai
 - conda: Please follow instructions [here](https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html) to manage environments:
 
 ```bash
-conda create -n synapseclient python=3.14
+conda create -n synapseclient python=3.15
 conda activate synapseclient
 
 # Here are a few ways to install the client. Choose the one that fits your use-case
@@ -43,8 +43,8 @@ to the `/usr/local/lib` directory. [See here](https://github.com/conda/conda/iss
 - pyenv: Use [virtualenv](https://virtualenv.pypa.io/en/latest/) to manage your python environment:
 
 ```bash
-pyenv install -v 3.14.0
-pyenv global 3.14.0
+pyenv install -v 3.15.0
+pyenv global 3.15.0
 python -m venv env
 source env/bin/activate
 
diff --git a/setup.cfg b/setup.cfg
index 3e9085626..4cc209800 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -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
     Operating System :: MacOS
     Operating System :: Microsoft :: Windows
     Operating System :: Unix
@@ -41,7 +42,7 @@ classifiers =
 zip_safe = False
 include_package_data = True
 packages = find:
-python_requires = >=3.11, <3.15
+python_requires = >=3.11, <3.16
 install_requires =
     requests>=2.34.0,<3.0
     urllib3>=2.8.0
diff --git a/synapseclient/core/download/download_functions.py b/synapseclient/core/download/download_functions.py
index 14d211f99..71d83d54f 100644
--- a/synapseclient/core/download/download_functions.py
+++ b/synapseclient/core/download/download_functions.py
@@ -973,7 +973,7 @@ def _ftp_report_hook(
                 destination=destination, file_handle_id=file_handle_id
             )
             range_header = (
-                {"Range": f"bytes={os.path.getsize(filename=temp_destination)}-"}
+                {"Range": f"bytes={os.path.getsize(temp_destination)}-"}
                 if os.path.exists(temp_destination)
                 else {}
             )
@@ -1103,7 +1103,7 @@ def _ftp_report_hook(
                 # Servers that respect the Range header return 206 Partial Content
                 if response.status_code == 206:
                     mode = "ab"
-                    previously_transferred = os.path.getsize(filename=temp_destination)
+                    previously_transferred = os.path.getsize(temp_destination)
                     to_be_transferred += previously_transferred
                     transferred += previously_transferred
                     increment_progress_bar_total(
diff --git a/tests/unit/synapseclient/core/unit_test_download.py b/tests/unit/synapseclient/core/unit_test_download.py
index 826a3c8dc..8b18a1798 100644
--- a/tests/unit/synapseclient/core/unit_test_download.py
+++ b/tests/unit/synapseclient/core/unit_test_download.py
@@ -986,9 +986,7 @@ async def test_download_end_early_retry(self, syn: Synapse) -> None:
 
             # assert getsize() called 2 times
             # once because exists()=True and another time because response status code = 206
-            assert [
-                call(filename=temp_destination)
-            ] * 2 == mocked_getsize.call_args_list
+            assert [call(temp_destination)] * 2 == mocked_getsize.call_args_list
 
             # assert shutil.move() called 1 time
             mocked_move.assert_called_once_with(temp_destination, destination)