💡 Motivation and Context

Capture v1 sends processing options (process_person_profile, cookieless_mode, disable_skew_correction, product_tour_id) in a per-event options object. Until now the SDK only filled it from legacy $ properties, coerced the values, and gave callers no way to set options directly. posthog-go and posthog-rs v1 already take per-event options and send them as given.

New options argument on capture, capture_ai, set, set_once, group_identify, alias and capture_exception, on Client, AsyncPosthog and the module-level functions. For example: posthog.capture("signed_up", distinct_id=..., options={"cookieless_mode": True}).

Behavior changes:

• Options are sent as given. The SDK checks neither keys nor value types; PostHog validates them. Unknown keys pass through. A value that is not a dict is logged as an error, and the event is sent without it.
• Legacy properties are no longer coerced. $cookieless_mode, $ignore_sent_at, $product_tour_id and $process_person_profile still fill the matching option, unchanged. Before, "true" became True and an unparseable value was dropped. The property is always removed from properties.
• An option wins over its legacy property. A null option counts as unset, so the property fills it. This matches go and rs.
• The legacy properties move into options once, after before_send. That was already the case. before_send now also sees options and can change it.
• Event uuids accept only the forms other SDKs accept:
  • hyphenated, 32 hex, {...} braced and urn:uuid: in any case; each is canonicalized
  • anything else, such as Python's uuid: prefix or misplaced hyphens, is replaced with a generated uuid and logged
  • this now applies to AsyncPosthog too, which before accepted anything uuid.UUID() parses
• Minimal $feature_flag_called events keep $cookieless_mode, $ignore_sent_at, $product_tour_id and $window_id. The allowlist runs before the legacy properties move into options, so these were dropped and their options lost. posthog-go has the same fix in feat!: add default and request-context options; event values win over defaults posthog-go#359.

Not in this PR: global and context options, the layer-order change, and the personless option (next PR in the stack), and AI wrappers and MCP moving to options (the one after).

💚 How did you test it?

• Wire builder:
  • each legacy property fills its option unchanged
  • option vs legacy, with the option set, null or missing
  • unknown options pass through
  • a non-dict is logged and ignored
  • the input is not mutated
  • accepted and rejected uuid forms
• Clients: new test_event_options.py. It checks that options reaches the wire from every method on Client and AsyncPosthog. A before_send that returns a new event can change options and remove a legacy property. A non-dict options is logged and the event is still sent.
• Minimal flag events: a gated event with legacy option super properties keeps the options and window_id.
• Break-on-purpose: each of these was reverted in turn, and the matching test failed every time:
  • the legacy property winning
  • alias dropping options
  • the four allowlist keys
  • lenient uuid parsing
  • async capture dropping options
  • sync and async ignoring the hook's options
• I ran ruff, mypy (baseline), the strict type smoke, the full pytest suite, the adapter tests, python -W error -c "import posthog", the public API snapshot and uv lock --check.

📝 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

Covered by the existing capture-v1-major changeset; the migration guide lands later in this stack.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Written with Cursor (Claude Opus) under the direction of the assignee.

Agreed before implementation:

• options pass through unchanged
• non-dict options logged and ignored
• only string $session_id/$window_id move to top-level fields
• hoisting once, after before_send
• an option wins over its legacy property
• the uuid forms, matching posthog-go uuid.Validate

Agent calls worth review:

• the queued message always carries options (maybe {}), so before_send sees the key
• a null legacy property still fills an unset option as null, as in posthog-rs