New Adapter: fx by Vercel

Traces Team

Aug 20, 20262 min read

Traces CLI v0.6.20 adds support for fx. fx is the new open-source coding agent from Vercel Labs.

What is fx?

fx is a coding agent built by Vercel Labs in Zig. The Vercel team optimized it for three things: raw speed, ease of use in low-resource environments, and model and provider openness.

How Traces reads fx

fx keeps every session on disk under ~/.fx/sessions/<id>/. Each session directory holds an event log plus a handful of metadata files, and Traces reads them directly. This means no plugin, daemon, or changes to your existing fx workflows.

Under the hood, Traces understands the full shape of an fx session:

The event log (events.jsonl). A stream of events discriminated by kind log things like session metadata, completed turns, and token-usage.
Compaction. When fx compacts a long conversation, the precompaction history is preserved as base64-encoded chunks. Traces reassembles those chunks so nothing from earlier in the session disappears from your shared trace.
Subagents. fx records parent/child links in each child's subagent/control.json. Traces follows those links so a session and everything spawned stay connected.

Titles come from fx's own display.json when present, and otherwise from the first prompt typed, which makes your sessions recognizable at a glance.

What you can do now

With this update, you can:

Share fx sessions. Publish any session with public access, private access, or a direct link. Traces resolves the right session automatically from your working directory, or you can point it at a specific session ID.
Resume fx sessions. Pick up your own work or a teammate's.
Connect fx sessions to git commits. Run traces setup to link a session to a commit so your history stays traceable from code back to the conversation that wrote it.

Get started

Update your CLI to v0.6.20.
Run traces setup to connect your fx sessions to your commits.
Run traces share to publish a session and get a link.

How Traces reads fx

Under the hood, Traces understands the full shape of an fx session:

The event log (events.jsonl). A stream of events discriminated by kind log things like session metadata, completed turns, and token-usage.

Compaction. When fx compacts a long conversation, the precompaction history is preserved as base64-encoded chunks. Traces reassembles those chunks so nothing from earlier in the session disappears from your shared trace.

Subagents. fx records parent/child links in each child's subagent/control.json. Traces follows those links so a session and everything spawned stay connected.

Titles come from fx's own display.json when present, and otherwise from the first prompt typed, which makes your sessions recognizable at a glance.

What you can do now

With this update, you can:

Share fx sessions. Publish any session with public access, private access, or a direct link. Traces resolves the right session automatically from your working directory, or you can point it at a specific session ID.

Resume fx sessions. Pick up your own work or a teammate's.

Connect fx sessions to git commits. Run traces setup to link a session to a commit so your history stays traceable from code back to the conversation that wrote it.