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Trace OpenCode terminal coding sessions, model calls, and tool usage with Arize AX for full observability.
OpenCode is an open-source AI coding agent built for the terminal. The Arize Coding Harness Tracing instruments OpenCode sessions with an in-process plugin and exports OpenInference spans to Arize AX. Each turn is captured as a trace, with nested spans for the model call and every tool invocation.

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Launch Arize AX

To get started, sign up for a free Arize AX account and get your Space ID and API Key:
  1. Log in at app.arize.com
  2. Click Settings and copy the Space ID
  3. Open the API Keys tab and create or copy an API key

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Install

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Curl installer

macOS / Linux:
Windows (PowerShell):

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Local clone

The installer prompts for your Arize AX credentials and project name, writes them to ~/.arize/harness/config.json, and copies the tracing plugin to ~/.config/opencode/plugin/arize-tracing.ts. OpenCode auto-discovers plugins from both the plugin/ and plugins/ directories under ~/.config/opencode/, so no opencode.json edit is required.

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Configuration

Credentials live in ~/.arize/harness/config.json. Environment variables override values in config.json and can be set in your shell profile so they apply to every OpenCode session.
If ARIZE_TRACE_ENABLED=false is set in your shell environment — for example, inherited from another harness’s configuration — tracing is silently disabled. Set ARIZE_TRACE_ENABLED=true before launching OpenCode, or unset the variable to fall back to the default of true.

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Redaction controls

Each ARIZE_LOG_* flag accepts "true" or "false" and defaults to "true". Set to "false" to opt out per category:

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Observe

Once tracing is enabled, OpenCode activity is streamed to Arize AX. Each turn (one user prompt to the assistant’s response) is captured as a trace.

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Spans Captured

Each turn produces a three-level span tree: Timestamps come from OpenCode’s own millisecond clocks rather than wall-clock time on the tracing process. The default project name is opencode unless you set ARIZE_PROJECT_NAME.

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How Tracing Works

OpenCode is architecturally different from the other coding agents in this repo. Extensions load as plugins inside OpenCode’s Bun runtime — there is no per-event subprocess. The integration has two pieces:
  1. A TypeScript plugin shim at ~/.config/opencode/plugin/arize-tracing.ts that listens for message.updated and session.idle events, pulls the authoritative session snapshot via the OpenCode SDK, and pipes it to the reconciler.
  2. A Python reconciler (arize-hook-opencode) that walks the snapshot and emits any new Turn, LLM, and TOOL spans, deduplicated by message ID and tool call ID. Spans are sent directly to Arize AX — no separate buffer or collector service is required.

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Limitations

Sub-agent and task sessions trace independently. OpenCode’s built-in task tool spawns sub-agents that each get their own sessionID. In v1, each sub-agent session produces its own independent trace; they are not linked back to the parent session’s trace.

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Reference

For the full list of environment variables, default file paths, and troubleshooting steps, see the OpenCode tracing README.

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Uninstall

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Resources

Arize Coding Harness Tracing

OpenInference

OpenCode