httpx Set Headers like Cookies in Client session for all

The Fix

Upgrade to version 0.7.2 or later.

Based on closed encode/httpx issue #149 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -20,7 +20,7 @@
 ```
 
-* `def __init__([auth], [cookies], [verify], [cert], [timeout], [pool_limits], [max_redirects], [app], [dispatch])`
+* `def __init__([auth], [headers], [cookies], [verify], [cert], [timeout], [pool_limits], [max_redirects], [app], [dispatch])`
 * `def .get(url, [params], [headers], [cookies], [auth], [stream], [allow_redirects], [verify], [cert], [timeout])`

repro.py

>> headers = Headers({"X-Auth-Token": "FooBarBazToken", "User-Agent": "python-myclient/0.2.1"})
>> session = Client(base_url="https://httpbin.org", headers=headers)

>> get_headers = session.get("/headers")

>> get_headers.json()
{'headers': {'Accept': '*/*',
  'Accept-Encoding': 'gzip, deflate',
  'Cookie': 'MyCookie=MyValue',
  'Host': 'httpbin.org',
  'User-Agent': 'python-myclient/0.2.1',
  'X-Auth-Token': 'FooBarBazToken'}}

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.7.2 or later.\nWhen NOT to use: Do not use this fix if you require headers to be set differently for individual requests.\n\n

Why This Fix Works in Production

Trigger: Users could not set headers for each request, impacting token-based authentication.
Mechanism: The BaseClient class did not support setting headers for requests
Why the fix works: Resolves #149 by adding `headers` as an argument to the `BaseClient` class, enabling users to set headers for each request. (first fixed release: 0.7.2).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

The BaseClient class did not support setting headers for requests
Production symptom (often without a traceback): Users could not set headers for each request, impacting token-based authentication.

Proof / Evidence

GitHub issue: #149
Fix PR: https://github.com/encode/httpx/pull/159
First fixed release: 0.7.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.55

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Indeed, yup! 👍 We've got a .cookies interface on there already, but we don't yet have a .headers interface.”

@lovelydinosaur · 2019-07-25 · source

“So there is a cookies= option! I missed it because I was searching so hard for headers. I'll update the OP.”

@StephenBrown2 · 2019-07-26 · source

Failure Signature (Search String)

Users could not set headers for each request, impacting token-based authentication.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Users could not set headers for each request, impacting token-based authentication.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Users could not set headers for each request, impacting token-based authentication.

Minimal Reproduction

repro.py

>> headers = Headers({"X-Auth-Token": "FooBarBazToken", "User-Agent": "python-myclient/0.2.1"})
>> session = Client(base_url="https://httpbin.org", headers=headers)

>> get_headers = session.get("/headers")

>> get_headers.json()
{'headers': {'Accept': '*/*',
  'Accept-Encoding': 'gzip, deflate',
  'Cookie': 'MyCookie=MyValue',
  'Host': 'httpbin.org',
  'User-Agent': 'python-myclient/0.2.1',
  'X-Auth-Token': 'FooBarBazToken'}}

What Broke

Users could not set headers for each request, impacting token-based authentication.

Why It Broke

The BaseClient class did not support setting headers for requests

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 0.7.2 or later.

When NOT to use: Do not use this fix if you require headers to be set differently for individual requests.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/encode/httpx/pull/159

First fixed release: 0.7.2

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not use this fix if you require headers to be set differently for individual requests.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
0.7.2	Fixed

Related Issues

No related fixes found.

Cluster: httpx:configuration-error All hubs All clusters

Related clusters: Data consistency Other Timeout

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

httpx Set Headers like Cookies in Client session for all requests (Fix)