deprecate env vars, add changelog

Author: lmolkova

CHANGELOG.md

@@ -11,6 +11,9 @@ release.
 
 ### Traces
 
+- Deprecate Zipkin exporter document and make exporter implementation optional
+  ([#4715](https://github.com/open-telemetry/opentelemetry-specification/pull/4715/))
+
 ### Metrics
 
 - `AlignedHistogramBucketExemplarReservoir` SHOULD use a time-weighted algorithm.

specification/configuration/sdk-environment-variables.md

@@ -15,32 +15,33 @@ aliases:
 
 <!-- toc -->
 
-- [Implementation guidelines](#implementation-guidelines)
-- [Parsing empty value](#parsing-empty-value)
-- [Configuration types](#configuration-types)
-  * [Boolean](#boolean)
-  * [Numeric](#numeric)
-    + [Integer](#integer)
-    + [Duration](#duration)
-    + [Timeout](#timeout)
-  * [String](#string)
-    + [Enum](#enum)
-- [General SDK Configuration](#general-sdk-configuration)
-- [Batch Span Processor](#batch-span-processor)
-- [Batch LogRecord Processor](#batch-logrecord-processor)
-- [Attribute Limits](#attribute-limits)
-- [Span Limits](#span-limits)
-- [LogRecord Limits](#logrecord-limits)
-- [OTLP Exporter](#otlp-exporter)
-- [Zipkin Exporter](#zipkin-exporter)
-- [Prometheus Exporter](#prometheus-exporter)
-- [Exporter Selection](#exporter-selection)
-  * [In-development Exporter Selection](#in-development-exporter-selection)
-- [Metrics SDK Configuration](#metrics-sdk-configuration)
-  * [Exemplar](#exemplar)
-  * [Periodic exporting MetricReader](#periodic-exporting-metricreader)
-- [Declarative configuration](#declarative-configuration)
-- [Language Specific Environment Variables](#language-specific-environment-variables)
+- [OpenTelemetry Environment Variable Specification](#opentelemetry-environment-variable-specification)
+  - [Implementation guidelines](#implementation-guidelines)
+  - [Parsing empty value](#parsing-empty-value)
+  - [Configuration types](#configuration-types)
+    - [Boolean](#boolean)
+    - [Numeric](#numeric)
+      - [Integer](#integer)
+      - [Duration](#duration)
+      - [Timeout](#timeout)
+    - [String](#string)
+      - [Enum](#enum)
+  - [General SDK Configuration](#general-sdk-configuration)
+  - [Batch Span Processor](#batch-span-processor)
+  - [Batch LogRecord Processor](#batch-logrecord-processor)
+  - [Attribute Limits](#attribute-limits)
+  - [Span Limits](#span-limits)
+  - [LogRecord Limits](#logrecord-limits)
+  - [OTLP Exporter](#otlp-exporter)
+  - [Zipkin Exporter](#zipkin-exporter)
+  - [Prometheus Exporter](#prometheus-exporter)
+  - [Exporter Selection](#exporter-selection)
+    - [In-development Exporter Selection](#in-development-exporter-selection)
+  - [Metrics SDK Configuration](#metrics-sdk-configuration)
+    - [Exemplar](#exemplar)
+    - [Periodic exporting MetricReader](#periodic-exporting-metricreader)
+  - [Declarative configuration](#declarative-configuration)
+  - [Language Specific Environment Variables](#language-specific-environment-variables)
 
 <!-- tocstop -->
 
@@ -270,6 +271,8 @@ See [OpenTelemetry Protocol Exporter Configuration Options](../protocol/exporter
 
 ## Zipkin Exporter
 
+**Status**: [Deprecated](../../document-status.md)
+
 | Name                          | Description                                                                        | Default                              | Type        |
 |-------------------------------|------------------------------------------------------------------------------------|--------------------------------------|-------------|
 | OTEL_EXPORTER_ZIPKIN_ENDPOINT | Endpoint for Zipkin traces                                                         | `http://localhost:9411/api/v2/spans` | [String][]  |
@@ -308,7 +311,7 @@ The implementation MAY accept a comma-separated list to enable setting multiple
 Known values for `OTEL_TRACES_EXPORTER` are:
 
 - `"otlp"`: [OTLP](https://opentelemetry.io/docs/specs/otlp/)
-- `"zipkin"`: [Zipkin](https://zipkin.io/zipkin-api/) (Defaults to [protobuf](https://github.com/openzipkin/zipkin-api/blob/master/zipkin.proto) format)
+- `"zipkin"`: [Zipkin](https://zipkin.io/zipkin-api/) (Defaults to [protobuf](https://github.com/openzipkin/zipkin-api/blob/master/zipkin.proto) format).
 - `"console"`: [Standard Output](../trace/sdk_exporters/stdout.md)
 - `"logging"`: [Standard Output](../trace/sdk_exporters/stdout.md). It is a deprecated value left for backwards compatibility. It SHOULD
 NOT be supported by new implementations.

specification/trace/sdk_exporters/zipkin.md

@@ -6,8 +6,6 @@ linkTitle: Zipkin
 
 **Status**: [Deprecated](../../document-status.md)
 
-Zipkin exporter support will be removed from OpenTelemetry specification in Jan 2027.
-
 _Note: This document remains here for backwards compatibility and
 will be removed in a future version. SDKs MAY include Zipkin exporters,
 but Zipkin exporter is not required.