Getting started

FIX Classic provides institutional connectivity for firms that operate established FIX session and tag-value message workflows.

Your session package is authoritative

Use the Polyester dictionary and session profile assigned to your connection. Generic FIX dictionaries do not define the fields, workflows, or limits enabled for your session.

When to use FIX Classic

Use FIX Classic when your integration requires:

established FIX session tooling
operational sequence and recovery workflows
institutional onboarding and certification
integration with existing order-management infrastructure

Use FIX-SBE when you need FIX session behavior with fixed-layout binary application messages.

Integration flow

Review the session package

Confirm the assigned FIX versions, dictionary, CompIDs, endpoint, authentication method, enabled business workflows, and operational limits.

Implement session behavior

Implement logon, heartbeat, sequence persistence, resend, reset, logout, and recovery exactly as defined by the session profile.

Validate application messages

Generate or configure message types from the assigned Polyester dictionary. Reject messages that do not match the required fields, enums, and extensions.

Complete certification

Run the conformance and recovery cases for the assigned workflows before connecting the production session.

Recovery boundaries

Persist sequence state and follow the assigned resend and reset policy. Session recovery restores FIX protocol sequence.

See the Connectivity matrix to combine FIX with REST, ConnectRPC, or WebSocket realtime.