November 2025 monthly summary for envoyproxy/envoy: Implemented Upstream First Byte Timing Observability to enhance upstream latency visibility and debugging capabilities. Key changes include recording the time when the first byte of the upstream response body is received, using a monotonic clock, and emitting a timing log entry with an optional deferred histogram. Changes were made in UpstreamCodecFilter and related structures (e.g., CodecBridge::decodeData) to capture and log the timing. The work includes unit/integration tests and user documentation, plus a Release Notes entry describing the new US_RX_BODY_BEG metric in access_log. This feature directly supports improved observability, faster root-cause analysis for upstream latency, and more actionable performance data for operators. It aligns with ongoing efforts to make tracing and latency metrics more precise in production deployments.