Sidechain Rate
What It Measures
The fraction of messages in a session that occurred on sidechain branches — alternate reasoning paths the model explored and then abandoned. Sidechain messages represent work the model did that didn't contribute to the final output.
Why It Matters
When Claude Code backtracks, it creates sidechain branches — invisible to the user but consuming tokens and time. A high sidechain rate means the model is frequently going down wrong paths before finding the right approach. This is a direct measure of wasted effort.
Tracking sidechain rate helps identify tasks or prompting patterns that confuse the model. If certain types of requests consistently produce high sidechain rates, that's a signal to improve prompt clarity, provide better context via CLAUDE.md, or break the task into smaller pieces.
How It's Calculated
sidechain_rate = sidechain_messages / (human_messages + assistant_messages)
Summed across all sessions correlated to the PR. Returns a value between 0.0 and 1.0. Returns null if there are no messages.
Data Sources Required
- Claude Code session data — Message-level
isSidechainflag from session JSONL files.