Mixpanel /decide and /flags Requests Failing
Quick answer
The /decide endpoint was decommissioned in August 2026. Upgrade the SDK to v2.45.0 or later and make sure proxies forward the Authorization header for /flags.
Most likely fix: Upgrade the SDK
How to fix it
Try these in order — the most common fix is first.
1. Upgrade the SDK
- Move to JavaScript SDK v2.45.0 or later
- Remove custom /decide proxy rules
Did this fix it?2. Fix the proxy
- Forward Authorization on /flags
- Strip the path prefix (docs reference /_mp/)
Did this fix it?
Symptoms
Failing /decide calls or 401 on /flags behind a proxy.
Why it happens
- Old SDK still calls /decide
- Proxy drops the Authorization header
- Proxy path prefix not stripped
This guide also covers
- mixpanel decide endpoint
- mixpanel flags 401
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