fix(capture): keep $release_id on minimized flag-called events

[posthog]

💡 Motivation and Context

Contract: capture — "Environment-sourced release identifier".

The spec states:

$release_id is a static, low-cardinality runtime identity property in the sense of the feature-flag-called-tracker minimal-event allowlist, so a minimized $feature_flag_called event SHALL retain it when the SDK stamped it.

with the acceptance scenario "A minimized flag-called event keeps the release id (@server)".

The sdk-specs compliance matrix for this SDK records the gap on the Capture row:

$release_id is not in _MINIMAL_FLAG_CALLED_EVENT_PROPERTIES, and the allowlist filter runs after the release-id stamp, so a minimized $feature_flag_called strips the property the capture spec says it SHALL retain.

Backwards compatibility: Backward-compatible — adding $release_id to the allowlist frozenset is a one-line additive change.

Remediation: Add "$release_id" to _MINIMAL_FLAG_CALLED_EVENT_PROPERTIES (it is a static, low-cardinality runtime identity property, exactly the category the allowlist already keeps $lib/$os for).

The spec proposal that introduced the requirement notes PHP and Ruby already behave this way and that Python needs this follow-up.

Changes

• Add "$release_id" to _MINIMAL_FLAG_CALLED_EVENT_PROPERTIES in posthog/client.py. The stamp in _enqueue() already runs before the allowlist filter, so no ordering change is needed.
• Replace test_minimal_flag_called_events_keep_their_strict_allowlist (which asserted the old, non-compliant stripping) with coverage that the release id survives minimization while everything outside the allowlist — caller properties and super properties — is still stripped, plus a case where the env var is unset.
• Add an end-to-end regression mirroring the spec scenario: a gated, non-experiment flag resolved through /flags emits a minimized $feature_flag_called carrying $release_id.
• Pin POSTHOG_RELEASE_ID in the minimization test mixin, so the exact-shape assertions no longer depend on whether the test runner happens to export the variable.

Why this is backwards-compatible

Purely additive: one more key is allowed through an existing filter. Nothing is removed or renamed, no public API or signature changes, no default changes, and events that never had a release id are byte-identical. $release_id only appears when POSTHOG_RELEASE_ID is set — which already caused the property to appear on every other event this SDK sends.

💚 How did you test it?

• Both new assertions fail on the pre-fix tree and pass after it.
• pytest posthog/test/test_release_id.py posthog/test/test_feature_flag_called_minimization.py — 48 passed.
• Full suite: pytest posthog/test — 4582 passed, 6 skipped, 52 subtests passed. The 8 failures are pre-existing AI-provider integration tests that require live OPENAI_API_KEY credentials and are unrelated to this change.
• ruff check / ruff format --check, mypy --no-site-packages | mypy-baseline filter (no issues in 298 files), python -W error -c "import posthog", and make public_api_check (snapshot up to date) all pass.

Follow-up work

Not in scope here, tracked as separate gaps on the same Capture row: the SDK still has no dynamic runtime opt-out API distinct from the constructor-time disabled switch (being addressed in #1047).

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

🤖 Agent context

Autonomy: Fully autonomous

Produced by the scheduled SDK-compliance workflow, which reads the compliance matrices in PostHog/sdk-specs and implements one well-scoped, backwards-compatible gap per run. This cell was picked over the other open gaps because the remediation is a single additive allowlist entry against an explicit SHALL with a named acceptance scenario, on a widely-used contract. No human directed the work; leaving it unassigned for the owning team to triage.

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Created with PostHog Desktop

🤖 Generated with Claude Code

[github-actions]

posthog-python Compliance Report

Date: 2026-10-13T06:10:47.834532+00:00
Duration: 259951ms

✅ All Tests Passed!

121/121 tests passed

---

Capture_V1 Tests

✅ 95/95 tests passed

View Details

Test	Status	Duration
Endpoint And Method.Targets V1 Endpoint	✅	518ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	511ms
Required Headers.Has Authorization Bearer Header	✅	511ms
Required Headers.Has Content Type Json	✅	511ms
Required Headers.Has Posthog Sdk Info Format	✅	510ms
Required Headers.Has Posthog Attempt Header	✅	511ms
Required Headers.Has Posthog Request Id	✅	510ms
Required Headers.Has Posthog Request Timestamp	✅	510ms
Required Headers.Has User Agent	✅	510ms
Body Format.Body Has Created At And Batch	✅	510ms
Body Format.No Api Key In Body	✅	511ms
Body Format.No Sent At In Body	✅	510ms
Event Format.Event Has Required Root Fields	✅	510ms
Event Format.Event Uuid Is Valid	✅	511ms
Event Format.Event Timestamp Is Rfc3339	✅	510ms
Event Format.Non Utc Event Timestamp Is Converted To Utc	✅	515ms
Event Format.Distinct Id Is String	✅	511ms
Event Format.Distinct Id At Root Not Properties	✅	510ms
Event Format.Custom Properties Preserved	✅	510ms
Event Format.Set Properties Preserved	✅	510ms
Event Format.Set Once Properties Preserved	✅	511ms
Event Format.Groups Properties Preserved	✅	510ms
Event Format.Sdk Generates Uuid If Not Provided	✅	510ms
Event Format.Event Has Required Root Fields Batch	✅	514ms
Event Format.Event Uuid Is Valid Batch	✅	514ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	513ms
Event Format.Distinct Id Is String Batch	✅	514ms
Event Format.Distinct Id At Root Not Properties Batch	✅	514ms
Event Format.Custom Properties Preserved Batch	✅	514ms
Event Format.Set Properties Preserved Batch	✅	514ms
Event Format.Set Once Properties Preserved Batch	✅	514ms
Event Format.Groups Properties Preserved Batch	✅	514ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	514ms
Batch Behavior.Multiple Events In Single Batch	✅	517ms
Batch Behavior.Batch Envelope Smoke	✅	516ms
Batch Behavior.Flush With No Events Sends Nothing	✅	507ms
Batch Behavior.Flush At Triggers Batch	✅	1012ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	511ms
Deduplication.Generates Unique Uuids	✅	517ms
Deduplication.Different Events Same Content Different Uuids	✅	513ms
Deduplication.Preserves Uuid On Retry	✅	6520ms
Deduplication.Preserves Timestamp On Retry	✅	6520ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6522ms
Deduplication.No Duplicate Events In Batch	✅	519ms
Header Behavior On Retry.Attempt Header Starts At One	✅	510ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	13529ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	6516ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3021ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	6516ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	512ms
Response Format Validation.Success Response Has Ok For Each Event	✅	514ms
Response Format Validation.Success No Retry After When All Ok	✅	513ms
Response Format Validation.Success Retry After Present When Retry Events	✅	1516ms
Response Format Validation.Success No Retry After When Drop Only	✅	513ms
Response Format Validation.Response Echoes Request Id	✅	510ms
Retry Behavior.Retries On 408	✅	6520ms
Retry Behavior.Retries On 500	✅	6517ms
Retry Behavior.Retries On 503	✅	8519ms
Retry Behavior.Retries On 504	✅	6516ms
Retry Behavior.Retryable Errors Have Retry After	✅	3518ms
Retry Behavior.Respects Retry After On Retryable Error	✅	11523ms
Retry Behavior.Does Not Retry On 400	✅	2514ms
Retry Behavior.Does Not Retry On 401	✅	2514ms
Retry Behavior.Does Not Retry On 402	✅	2514ms
Retry Behavior.Does Not Retry On 413	✅	2514ms
Retry Behavior.Does Not Retry On 415	✅	2513ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	2514ms
Retry Behavior.Implements Backoff	✅	22536ms
Retry Behavior.Max Retries Respected	✅	22537ms
Partial Batch Handling.Handles 200 Full Success	✅	2514ms
Partial Batch Handling.Handles 200 With All Ok	✅	3515ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	3515ms
Partial Batch Handling.Does Not Retry Limited Events	✅	3517ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	6521ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	6522ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	6523ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	6522ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	6521ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	6521ms
Partial Batch Handling.Respects Retry After On Partial	✅	8519ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	3517ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	3520ms
Compression.Sends Gzip Content Encoding	✅	511ms
Compression.No Content Encoding When Disabled	✅	511ms
Compression.Compressed Body Is Decompressible	✅	510ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	2511ms
Event Options.Cookieless Mode Override	✅	511ms
Event Options.Disable Skew Correction Override	✅	509ms
Event Options.Process Person Profile Override	✅	511ms
Event Options.Product Tour Id Override	✅	510ms
Event Options.Unset Options Omitted	✅	511ms
Event Options.Options Override In Batch	✅	514ms
Geoip And Historical Migration.Geoip Disable Injected Into Properties	✅	510ms
Geoip And Historical Migration.Historical Migration Set In Body	✅	511ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	510ms

Capture_Ai Tests

✅ 5/5 tests passed

View Details

Test	Status	Duration
Routing.Capture Ai Posts To Ai Endpoint	✅	511ms
Routing.Capture Does Not Reroute Ai Named Events	✅	511ms
Identity.Capture Ai Event Has Uuid	✅	510ms
Identity.Capture Ai Keeps Supplied Uuid	✅	511ms
Timestamp Format.Non Utc Event Timestamp Is Converted To Utc	✅	510ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	12ms
Request Payload.Flags Request Uses V2 Query Param	✅	11ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	10ms
Request Payload.Flags Request Omits Authorization Header	✅	11ms
Request Payload.Token In Flags Body Matches Init	✅	11ms
Request Payload.Groups Round Trip	✅	11ms
Request Payload.Groups Default To Empty Object	✅	11ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	11ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	10ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	10ms
Request Lifecycle.No Flags Request On Init Alone	✅	4ms
Request Lifecycle.No Flags Request On Normal Capture	✅	510ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	14ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	10ms
Retry Behavior.Retries Flags On 502	✅	314ms
Retry Behavior.Retries Flags On 504	✅	313ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	513ms

Feature_Flags_Local_Evaluation Tests

✅ 4/4 tests passed

View Details

Test	Status	Duration
Versioned Boolean Matching.Matching Version Missing	✅	74ms
Versioned Boolean Matching.Matching Version 1	✅	70ms
Versioned Boolean Matching.Matching Version 2	✅	70ms
Versioned Boolean Matching.Version Only Reload 1 2 1 2 Missing	✅	36ms