feat: is_enabled() accepts a caller-supplied default_value (sdk-specs is-feature-enabled)

[posthog]

💡 Motivation and Context

The sdk-specs is-feature-enabled contract requires the boolean flag check to accept a caller-supplied boolean default:

• openspec/specs/is-feature-enabled/spec.md — Requirement: Canonical is-feature-enabled behavior: "The SDK SHALL accept a caller-supplied boolean default (defaultValue; parameter placement per platform idiom) and SHALL return it whenever the flag has no value: flags not loaded yet, a failed flags request, or no flag with that key in the loaded flags. A flag that has a value — including false and variant strings — always wins over the caller-supplied default."
• Same file, Server-side canonical signature lists defaultValue?: boolean alongside groups, personProperties, onlyEvaluateLocally, etc.
• Same file, scenarios "Enabled check resolves missing flags to the default" and "Enabled check prefers the flag value over the caller default".

What was out of compliance: FeatureFlagEvaluations.is_enabled(key) — the boolean check on the current, non-deprecated evaluate_flags() path — had no default parameter and hard-coded False for the no-value case. Callers had no way to make a missing flag, an empty evaluation, or a failed /flags request fall back to True.

Notably, the spec change that added this contract (sdk-specs#14 / #15) assumed the server SDKs already exposed it. posthog-python did not.

How this fixes it: is_enabled() gains default_value: bool = False, returned when the key is absent from the snapshot. A flag that has a value still wins, so a disabled flag returns False even with default_value=True.

The deprecated Client.feature_enabled() is intentionally not changed — it is already slated for removal in favor of evaluate_flags(...).is_enabled(key), so the contract is satisfied on the path callers are being steered toward.

💚 How did you test it?

• New tests in posthog/test/test_evaluate_flags.py covering the three spec scenarios: a missing flag returns the caller default (both False and True), a flag that has a value beats the default (disabled/boolean/variant), and a failed /flags request returns the default.
• uv run pytest posthog/test/test_evaluate_flags.py — 35 passed.
• ruff format --check ., ruff check ., mypy … | mypy-baseline filter — all clean.
• make public_api_snapshot regenerated references/public_api_snapshot.txt (the one changed signature line).

Behavior change / back-compat risk: none for existing callers. default_value defaults to False, which is exactly what is_enabled() returned before for missing flags. The only observable change is additive: passing default_value=True now returns True instead of False for a flag with no value. Public API surface grows by one optional parameter.

📝 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

Opened by the SDK Spec Compliance Enforcer loop, which audits posthog-python against the PostHog/sdk-specs contracts and files one focused PR per confirmed divergence.

• Tools: Claude Code (Bash, Read, Edit, Write, Grep/Glob) plus four parallel read-only Explore subagents, one per group of in-scope capabilities.
• This run audited ~22 both-scoped specs. Other candidate divergences were found and deliberately not included here to keep the PR focused, or skipped outright: the module-level get_feature_flag_payload tracking default was already filed as fix: don't send $feature_flag_called from module-level get_feature_flag_payload #794 and closed wontfix; the explicit-flush-bypasses-flush_interval gap is already open as fix: flush() delivers pending events without waiting out flush_interval #797; alias/group_identify missing-identifier validation and SizeLimitedDict's wholesale clear at capacity are behavior-changing and left for human triage.
• default_value was placed on FeatureFlagEvaluations.is_enabled() rather than the deprecated Client.feature_enabled(), since the spec allows platform-idiomatic parameter placement and modifying a deprecated surface adds churn without helping callers.

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Created with PostHog Code

[github-actions]

posthog-python Compliance Report

Date: 2026-07-30 08:00:44 UTC
Duration: 338834ms

✅ All Tests Passed!

111/111 tests passed

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Capture_V1 Tests

✅ 94/94 tests passed

View Details

Test	Status	Duration
Endpoint And Method.Targets V1 Endpoint	✅	518ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	1009ms
Required Headers.Has Authorization Bearer Header	✅	1009ms
Required Headers.Has Content Type Json	✅	1009ms
Required Headers.Has Posthog Sdk Info Format	✅	1009ms
Required Headers.Has Posthog Attempt Header	✅	1008ms
Required Headers.Has Posthog Request Id	✅	1008ms
Required Headers.Has Posthog Request Timestamp	✅	1010ms
Required Headers.Has User Agent	✅	1009ms
Body Format.Body Has Created At And Batch	✅	1009ms
Body Format.No Api Key In Body	✅	1008ms
Body Format.No Sent At In Body	✅	1009ms
Event Format.Event Has Required Root Fields	✅	1008ms
Event Format.Event Uuid Is Valid	✅	1009ms
Event Format.Event Timestamp Is Rfc3339	✅	1009ms
Event Format.Distinct Id Is String	✅	1009ms
Event Format.Distinct Id At Root Not Properties	✅	1008ms
Event Format.Custom Properties Preserved	✅	1009ms
Event Format.Set Properties Preserved	✅	1009ms
Event Format.Set Once Properties Preserved	✅	1008ms
Event Format.Groups Properties Preserved	✅	1009ms
Event Format.Sdk Generates Uuid If Not Provided	✅	1009ms
Event Format.Event Has Required Root Fields Batch	✅	1013ms
Event Format.Event Uuid Is Valid Batch	✅	1012ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	1011ms
Event Format.Distinct Id Is String Batch	✅	1013ms
Event Format.Distinct Id At Root Not Properties Batch	✅	1012ms
Event Format.Custom Properties Preserved Batch	✅	1013ms
Event Format.Set Properties Preserved Batch	✅	1012ms
Event Format.Set Once Properties Preserved Batch	✅	1012ms
Event Format.Groups Properties Preserved Batch	✅	1012ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	1013ms
Batch Behavior.Multiple Events In Single Batch	✅	1507ms
Batch Behavior.Batch Envelope Smoke	✅	1014ms
Batch Behavior.Flush With No Events Sends Nothing	✅	1005ms
Batch Behavior.Flush At Triggers Batch	✅	1508ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	1011ms
Deduplication.Generates Unique Uuids	✅	1507ms
Deduplication.Different Events Same Content Different Uuids	✅	1507ms
Deduplication.Preserves Uuid On Retry	✅	7515ms
Deduplication.Preserves Timestamp On Retry	✅	7513ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7511ms
Deduplication.No Duplicate Events In Batch	✅	1505ms
Header Behavior On Retry.Attempt Header Starts At One	✅	1009ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	14517ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	7514ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3517ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	7514ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	1005ms
Response Format Validation.Success Response Has Ok For Each Event	✅	1507ms
Response Format Validation.Success No Retry After When All Ok	✅	1507ms
Response Format Validation.Success Retry After Present When Retry Events	✅	2511ms
Response Format Validation.Success No Retry After When Drop Only	✅	1507ms
Response Format Validation.Response Echoes Request Id	✅	1009ms
Retry Behavior.Retries On 408	✅	7516ms
Retry Behavior.Retries On 500	✅	7512ms
Retry Behavior.Retries On 503	✅	9514ms
Retry Behavior.Retries On 504	✅	7513ms
Retry Behavior.Retryable Errors Have Retry After	✅	4507ms
Retry Behavior.Respects Retry After On Retryable Error	✅	12518ms
Retry Behavior.Does Not Retry On 400	✅	3503ms
Retry Behavior.Does Not Retry On 401	✅	3507ms
Retry Behavior.Does Not Retry On 402	✅	3509ms
Retry Behavior.Does Not Retry On 413	✅	3506ms
Retry Behavior.Does Not Retry On 415	✅	3508ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	3508ms
Retry Behavior.Implements Backoff	✅	23522ms
Retry Behavior.Max Retries Respected	✅	23531ms
Partial Batch Handling.Handles 200 Full Success	✅	2998ms
Partial Batch Handling.Handles 200 With All Ok	✅	4510ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	4508ms
Partial Batch Handling.Does Not Retry Limited Events	✅	4509ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	7509ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	7517ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	7512ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	7511ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	7509ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	7516ms
Partial Batch Handling.Respects Retry After On Partial	✅	9511ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	4507ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	4508ms
Compression.Sends Gzip Content Encoding	✅	1008ms
Compression.No Content Encoding When Disabled	✅	1008ms
Compression.Compressed Body Is Decompressible	✅	1010ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	3508ms
Event Options.Cookieless Mode Override	✅	1008ms
Event Options.Disable Skew Correction Override	✅	1008ms
Event Options.Process Person Profile Override	✅	1008ms
Event Options.Product Tour Id Override	✅	1008ms
Event Options.Unset Options Omitted	✅	1009ms
Event Options.Options Override In Batch	✅	1012ms
Geoip And Historical Migration.Geoip Disable Injected Into Properties	✅	1008ms
Geoip And Historical Migration.Historical Migration Set In Body	✅	1009ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	1009ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	1006ms
Request Payload.Flags Request Uses V2 Query Param	✅	1006ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	1007ms
Request Payload.Flags Request Omits Authorization Header	✅	1006ms
Request Payload.Token In Flags Body Matches Init	✅	1007ms
Request Payload.Groups Round Trip	✅	1007ms
Request Payload.Groups Default To Empty Object	✅	1006ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	1007ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	1006ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	1007ms
Request Lifecycle.No Flags Request On Init Alone	✅	503ms
Request Lifecycle.No Flags Request On Normal Capture	✅	1508ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	1010ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	1003ms
Retry Behavior.Retries Flags On 502	✅	1006ms
Retry Behavior.Retries Flags On 504	✅	1007ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	1509ms