zed-industries/zed · error

Anthropic ended the stream without finishing its compaction

Error message

Anthropic ended the stream without finishing its compaction summary

What it means

Anthropic closes every content block before message_stop. This error fires when Event::MessageStop arrives while compactions_by_index still holds an open compaction block: the finalized summary never arrived, and consumers would otherwise see a Started compaction with no terminal event and treat it as still in progress. The partial compaction state is cleared before erroring.

Source

Thrown at crates/anthropic/src/completion.rs:677

                        _ => {
                            log::error!("Unexpected anthropic stop_reason: {stop_reason}");
                            StopReason::EndTurn
                        }
                    };
                }
                vec![Ok(LanguageModelCompletionEvent::UsageUpdate(
                    convert_usage(&self.usage),
                ))]
            }
            Event::MessageStop => {
                // Anthropic closes every content block before ending the
                // message, so an unclosed compaction block means the stream
                // was malformed and its finalized summary never arrived.
                // Consumers would otherwise see `Started` with no terminal
                // event and treat the compaction as still in progress.
                if !self.compactions_by_index.is_empty() {
                    self.compactions_by_index.clear();
                    return vec![Err(LanguageModelCompletionError::Other(anyhow::anyhow!(
                        "Anthropic ended the stream without finishing its compaction summary"
                    )))];
                }
                vec![Ok(LanguageModelCompletionEvent::Stop(self.stop_reason))]
            }
            Event::Error { error } => {
                vec![Err(completion_error_from_anthropic_api(
                    error,
                    self.provider_name.clone(),
                ))]
            }
            _ => Vec::new(),
        }
    }
}

struct RawToolUse {
    id: String,

View on GitHub (pinned to bc538def45)

Solutions

1. Retry the completion - truncation is usually transient.
2. Check for proxy/VPN idle timeouts on long-lived streaming connections and raise them.
3. Reduce the conversation size before compaction triggers (clear or split the thread) so summaries stay short.
4. If it persists, report to Zed/Anthropic with the request id and stream log.

on stream end, if the final event is Err containing "without finishing its compaction summary", drop the partial compaction state and retry the completion once; otherwise surface the error to the UI layer.

When it happens

Trigger: The stream ends (MessageStop) with a compaction content block that was started but never closed - a dropped content_block_stop event, a connection cut mid-block, or upstream truncation of a long encrypted summary.

Common situations: Network interruptions during long compaction summaries; proxies that close long-lived SSE connections; very large encrypted summaries hitting server limits.

Related errors

• Anthropic streamed a compaction delta before starting its co
• unsupported Anthropic compaction state format: {}
• Claude returned no tool_use block for tool '{tool['name']}'
• Compaction produced an empty summary
• tool input was not fully received

AI-assisted analysis of zed-industries/zed@bc538def45 (2026-08-16). Data as JSON: /api/errors/5d0e246e7700a5cc. Report an issue: GitHub.