Everything in the served API reference is additive-only from the current compatibility baseline,
with one named exception.
Additive-only means a field or route documented here does not change meaning, does not change
type, and does not disappear. We may add new fields and new routes. Your integration should
ignore fields it does not recognize, and in return, the fields it does recognize will keep
working. You can build against this reference without watching for breaking-change
announcements, because there are none to watch for.
The current baseline began on 2026-09-06, before the first partner integration, when the account
stream was reshaped: the snapshot, positions and orders events were removed and the whole
account now arrives as one account event. That is a breaking change, and it is the reason the
baseline moved rather than something the additive-only rule can cover. There is no compatibility
shim and no dual delivery. The changelog states exactly what a pre-partner test client must change.
The baseline before it began on 2026-08-29, when Connect removed its draft handover request field
and emailSent response field.
The exception is the Challenges group. It is marked PREVIEW on every operation and its shapes
are outside the additive-only guarantee until the preview label comes off. If you build against
Challenges today, expect to revisit that code.
The guarantee is enforced, not promised. The build parses the engine’s own router and refuses a
key-reachable route that is missing from this reference, and every documented schema is locked
to the wire types the engine itself compiles against. A shape cannot drift from the wire, and a
route cannot ship undocumented, without failing the build.
