[BUG] The skill_activated event emits custom_skill instead of actual skill name

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When a skill is activated, the skill_activated OTel event sometimes records skill.name = "custom_skill" instead of the actual skill name.
This affects all three source types: plugin, projectSettings, and userSettings.

What's wrong is that skill.name is often custom_skill, and no other attribute in the event carries the real name.

What Should Happen?

I'd expect that skill.name contains the skill's actual name (e.g. brainstorming, review).

Error Messages/Logs

Steps to Reproduce

1. Enable Otel telemetry tracking through managed settings:

{
  "env": {
    "CLAUDE_CODE_ENABLE_TELEMETRY": "1",
    "OTEL_METRICS_EXPORTER": "otlp",
    "OTEL_LOGS_EXPORTER": "otlp",
    "OTEL_EXPORTER_OTLP_PROTOCOL": "http/json",
    "OTEL_EXPORTER_OTLP_ENDPOINT": "https://yourendpoint.com",
    "OTEL_LOG_USER_PROMPTS": "0",
    "OTEL_LOG_TOOL_DETAILS": "1",
    "CLAUDE_CODE_ENHANCED_TELEMETRY_BETA": "1",
    "OTEL_TRACES_EXPORTER": "otlp",
    "OTEL_EXPORTER_OTLP_HEADERS": "X-API-Key=YOUR_API_KEY",
    "CLAUDE_CODE_ENABLE_FEEDBACK_SURVEY_FOR_OTEL": "1"
  }
}

1. Have different users activate skills (manually or through model invocable skills).
2. Query your (BigQuery) data for the skill usage.

We've used this BigQuery data source in Google's Data Studio:

SELECT
  e.event_timestamp,
  e.user_email,
  e.session_id,
  e.terminal_type,
  (SELECT JSON_VALUE(a, '$.value.stringValue')
   FROM UNNEST(JSON_EXTRACT_ARRAY(e.raw_attributes)) a
   WHERE JSON_VALUE(a, '$.key') = 'skill.name')         AS skill_name,
  COALESCE(
   (SELECT JSON_VALUE(a, '$.value.stringValue')
    FROM UNNEST(JSON_EXTRACT_ARRAY(e.raw_attributes)) a
    WHERE JSON_VALUE(a, '$.key') = 'invocation_trigger'),
   '(unknown)')                                          AS invocation_trigger,
  (SELECT JSON_VALUE(a, '$.value.stringValue')
   FROM UNNEST(JSON_EXTRACT_ARRAY(e.raw_attributes)) a
   WHERE JSON_VALUE(a, '$.key') = 'skill.source')       AS skill_source,
  (SELECT JSON_VALUE(a, '$.value.stringValue')
   FROM UNNEST(JSON_EXTRACT_ARRAY(e.raw_attributes)) a
   WHERE JSON_VALUE(a, '$.key') = 'plugin.name')        AS plugin_name
FROM `maxxton-develop.mxt.claude_otel_events` e
WHERE e.event_type = 'skill_activated'

1. Notice that the most used skill is the "custom_skill", giving you no meaningful insight.

<img width="793" height="622" alt="Image" src="https://github.com/user-attachments/assets/61c3fd83-35f7-41fa-b97a-5d29743c619c" />

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.140

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

_No response_