Empty OPENAI_BASE_URL prevents fallback to default API endpoint

Confirm this is an issue with the Python library and not an underlying OpenAI API

This is an issue with the Python library

Describe the bug

I noticed a small issue in the base_url initialization logic: (

Lines 163 to 166 in 656e3ca

    
           if base_url is None: 
        
               base_url = os.environ.get("OPENAI_BASE_URL") 
        
           if base_url is None: 
        
               base_url = f"https://api.openai.com/v1"

)

if base_url is None:
    base_url = os.environ.get("OPENAI_BASE_URL")
if base_url is None:
    base_url = f"https://api.openai.com/v1"

If the environment variable OPENAI_BASE_URL is defined but empty (e.g., OPENAI_BASE_URL=""), then os.environ.get("OPENAI_BASE_URL") returns an empty string. As a result:

base_url becomes ""
the second condition (if base_url is None) is never triggered
the intended fallback "https://api.openai.com/v1" is skipped

An empty string is not a valid base URL, so this can lead to confusing behavior.

To Reproduce

export OPENAI_BASE_URL=""
run the following:

from openai import OpenAI

client = OpenAI()
client.models.list()

Trigger an "openai.APIConnectionError: Connection error" error

Code snippets

OS

macOS

Python version

Python 3.12.2

Library version

2.15.0

fix: treat empty OPENAI_BASE_URL as unset

fix: treat empty OPENAI_BASE_URL env var as unset

Good catch on the empty string edge case. The current logic:

if base_url is None:
    base_url = os.environ.get('OPENAI_BASE_URL')
if base_url is None:
    base_url = f'https://api.openai.com/v1'

...uses is None for both checks, but os.environ.get() returns an empty string '' (not None) when the variable is set but empty. Empty string is falsy but not None, so the fallback never triggers.

The fix should be:

if base_url is None:
    base_url = os.environ.get('OPENAI_BASE_URL') or None  # converts '' to None
if base_url is None:
    base_url = 'https://api.openai.com/v1'

Or equivalently:

base_url = base_url or os.environ.get('OPENAI_BASE_URL') or 'https://api.openai.com/v1'

Workaround: Unset the environment variable entirely (unset OPENAI_BASE_URL or del os.environ['OPENAI_BASE_URL']) rather than setting it to an empty string. The bug only triggers when OPENAI_BASE_URL is defined but empty — if it's not set at all, os.environ.get() returns None and the fallback works correctly.

This is addressed by #2939 — when OPENAI_BASE_URL is set to an empty string, it now falls back to the default API endpoint instead of constructing an invalid URL.

fix(client): treat empty OPENAI_BASE_URL as unset

I've submitted a fix for this in PR #2952. Uses or None to normalize empty env var strings, applied to both sync and async constructors.

fix: handle empty string in OPENAI_BASE_URL env var

This is a simple fix! I can submit a PR to handle the empty string case for OPENAI_BASE_URL.

fix(client): treat empty OPENAI_BASE_URL env var as unset

fix(client): treat empty OPENAI_BASE_URL as unset and fall back to de…

Opened #2988 for this.

The change only touches the environment fallback path: if OPENAI_BASE_URL is set to an empty string, the client now treats it the same as an unset value and falls back to the default API base URL. Explicit base_url arguments are left alone. I also added sync and async regressions for the empty-env case.

fix(client): treat empty OPENAI_BASE_URL as unset, falling back to de…

fix: treat empty OPENAI_BASE_URL same as None for default fallback

fix: treat empty OPENAI_BASE_URL env var as unset to restore default …

fix: treat empty OPENAI_BASE_URL env var as unset, fall back to default

A2ABench has an accepted answer for this imported thread.

Thread: https://a2abench-api.web.app/q/cmmpna7jk00ij1401e8s5i6jg
Accepted at: 2026-03-25T17:11:11.235Z
Accepted answer agent: ai village
Answer preview: "No matching threads were found for this query."

fix: handle empty OPENAI_BASE_URL fallback to default endpoint (fixes o…

Proposed Comprehensive Fix

I can confirm this bug affects both sync and async clients (src/openai/_client.py) and applies to not just OPENAI_BASE_URL but also potentially other empty-string environment variables. The Bedrock provider (src/openai/providers/bedrock.py) already handles this correctly using a _normalize_optional_string() helper.

Affected Locations (4 places in `_client.py`):

Sync client - line 306: base_url = os.environ.get("OPENAI_BASE_URL")
Async client - line 1066: base_url = os.environ.get("OPENAI_BASE_URL")
The bug also affects self._base_url_was_default tracking (lines 307 and 1067):
- Currently self._base_url_was_default = provider_runtime is None and base_url is None
- This incorrectly marks "" as user-provided instead of falling through to default

Proposed Fix Code:

Add a shared helper function in src/openai/_utils/_utils.py (or at top of _client.py):

def _get_env(name: str) -> str | None:
    """Get an environment variable, treating empty strings as unset."""
    value = os.environ.get(name)
    return value if value else None

Then replace all occurrences in src/openai/_client.py:

Line 305-310 (sync client):

if provider_runtime is not None:
    base_url = provider_runtime.base_url
elif base_url is None:
    base_url = _get_env("OPENAI_BASE_URL")
self._base_url_was_default = provider_runtime is None and base_url is None
self._data_residency = data_residency
if base_url is None:
    base_url = MTLS_API_BASE_URL if x509_identity is not None else "https://api.openai.com/v1"

Line 1065-1070 (async client):

if provider_runtime is not None:
    base_url = provider_runtime.base_url
elif base_url is None:
    base_url = _get_env("OPENAI_BASE_URL")
self._base_url_was_default = provider_runtime is None and base_url is None
self._data_residency = data_residency
if base_url is None:
    base_url = MTLS_API_BASE_URL if x509_identity is not None else "https://api.openai.com/v1"

This pattern matches what already exists in src/openai/providers/bedrock.py:30-35:

def _normalize_optional_string(value: str | None) -> str | None:
    if value is None:
        return None
    value = value.strip()
    return value or None

A more thorough fix would also apply this normalization to:

OPENAI_API_KEY (line 253, 1013)
OPENAI_ADMIN_KEY (line 263, 1023)
OPENAI_ORG_ID (line 279, 1039)
OPENAI_PROJECT_ID (line 283, 1043)
OPENAI_WEBHOOK_SECRET (line 287, 1047)
AZURE_OPENAI_ENDPOINT, AZURE_OPENAI_API_KEY, etc. in lib/azure.py

Using .strip() is also important for handling whitespace-only environment variable values which would also cause confusing failures.

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Empty OPENAI_BASE_URL prevents fallback to default API endpoint #2927

Confirm this is an issue with the Python library and not an underlying OpenAI API

Describe the bug

To Reproduce

Code snippets

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Python version

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Proposed Comprehensive Fix

Affected Locations (4 places in `_client.py`):

Proposed Fix Code:

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	if base_url is None:
	base_url = os.environ.get("OPENAI_BASE_URL")
	if base_url is None:
	base_url = f"https://api.openai.com/v1"

Empty OPENAI_BASE_URL prevents fallback to default API endpoint #2927

Description

Confirm this is an issue with the Python library and not an underlying OpenAI API

Describe the bug

To Reproduce

Code snippets

OS

Python version

Library version

Activity

xXMrNidaXx commented on Mar 8, 2026

giulio-leone commented on Mar 9, 2026

mvanhorn commented on Mar 10, 2026

passionworkeer commented on Mar 14, 2026

theamodhshetty commented on Mar 19, 2026

khalidsaidi commented on Mar 25, 2026

dajiaohuang commented on Sep 25, 2026

Proposed Comprehensive Fix

Affected Locations (4 places in _client.py):

Proposed Fix Code:

Metadata

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Labels

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Development

Issue actions

Affected Locations (4 places in `_client.py`):