Promote session config-option API to stable

session/set_config_option and session/set_mode are now part of the stable
ACP schema, so the @UnstableAcpApi marking on the config-option types was
stale. Remove it from:

- SetSessionConfigOptionRequest / SetSessionConfigOptionResponse
- SessionConfigOption, SessionConfigSelect, SessionConfigSelectOption
- ConfigOptionUpdate
- @SetSessionConfigOption

The boolean config-option variant (SessionConfigBoolean) keeps
@UnstableAcpApi: the stable schema only defines the select variant, so
boolean remains an SDK extension. session/set_mode types were never tagged
unstable and need no change.

Author: Mark Pollack

CHANGELOG.md

@@ -21,6 +21,14 @@ Protocol currency: catching up to ACP spec v0.13.6 (June 2026).
 - `sessionCapabilities.delete` and `sessionCapabilities.additionalDirectories`, surfaced via
   `NegotiatedCapabilities` (`supports*`/`require*`).
 
+### Changed
+
+- Promoted the session config-option API to stable: removed `@UnstableAcpApi` from
+  `SetSessionConfigOptionRequest`/`SetSessionConfigOptionResponse`, `SessionConfigOption`,
+  `SessionConfigSelect`, `SessionConfigSelectOption`, `ConfigOptionUpdate`, and `@SetSessionConfigOption`
+  — `session/set_config_option` and `session/set_mode` are now in the stable ACP schema. The
+  `boolean` config-option variant (`SessionConfigBoolean`) remains an unstable SDK extension.
+
 ### Deprecated
 
 - The session-model API — `session/set_model` (`setSessionModel`, `@SetSessionModel`, handler),

acp-annotations/src/main/java/com/agentclientprotocol/sdk/annotation/SetSessionConfigOption.java

@@ -20,7 +20,6 @@
  * @since 0.12.0
  * @see AcpAgent
  */
-@UnstableAcpApi
 @Target(ElementType.METHOD)
 @Retention(RetentionPolicy.RUNTIME)
 @Documented

acp-core/src/main/java/com/agentclientprotocol/sdk/spec/AcpSchema.java

@@ -632,7 +632,6 @@ public ForkSessionResponse(String sessionId, SessionModeState modes, SessionMode
 	/**
 	 * Set session config option request - changes a configuration value
 	 */
-	@UnstableAcpApi
 	@JsonIgnoreProperties(ignoreUnknown = true)
 	@JsonInclude(JsonInclude.Include.NON_NULL)
 	public record SetSessionConfigOptionRequest(@JsonProperty("sessionId") String sessionId,
@@ -658,7 +657,6 @@ public static SetSessionConfigOptionRequest bool(String sessionId, String config
 	/**
 	 * Set session config option response - returns full config state
 	 */
-	@UnstableAcpApi
 	@JsonIgnoreProperties(ignoreUnknown = true)
 	@JsonInclude(JsonInclude.Include.NON_NULL)
 	public record SetSessionConfigOptionResponse(
@@ -1233,14 +1231,14 @@ public record ModelInfo(@JsonProperty("modelId") String modelId, @JsonProperty("
 	}
 
 	// ---------------------------
-	// Session Config Types (UNSTABLE)
+	// Session Config Types
+	// (session/set_config_option is stable; the "boolean" variant remains an unstable extension)
 	// ---------------------------
 
 	/**
 	 * Session config option - a configurable setting exposed by the agent.
-	 * Discriminated by type: "select" or "boolean".
+	 * Discriminated by type: "select" (stable) or "boolean" (unstable extension).
 	 */
-	@UnstableAcpApi
 	@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
 	@JsonSubTypes({ @JsonSubTypes.Type(value = SessionConfigSelect.class, name = "select"),
 			@JsonSubTypes.Type(value = SessionConfigBoolean.class, name = "boolean") })
@@ -1251,7 +1249,6 @@ public interface SessionConfigOption {
 	/**
 	 * Select-type config option - a dropdown with named values.
 	 */
-	@UnstableAcpApi
 	@JsonIgnoreProperties(ignoreUnknown = true)
 	@JsonInclude(JsonInclude.Include.NON_NULL)
 	public record SessionConfigSelect(@JsonProperty("type") String type, @JsonProperty("id") String id,
@@ -1268,6 +1265,9 @@ public SessionConfigSelect(String id, String name, String currentValue,
 
 	/**
 	 * Boolean-type config option - a toggle.
+	 *
+	 * <p>Unstable: the stable schema only defines the {@code select} config option variant;
+	 * {@code boolean} is an SDK extension that may change.
 	 */
 	@UnstableAcpApi
 	@JsonIgnoreProperties(ignoreUnknown = true)
@@ -1285,7 +1285,6 @@ public SessionConfigBoolean(String id, String name, Boolean currentValue) {
 	/**
 	 * A selectable option within a select-type config option.
 	 */
-	@UnstableAcpApi
 	@JsonIgnoreProperties(ignoreUnknown = true)
 	@JsonInclude(JsonInclude.Include.NON_NULL)
 	public record SessionConfigSelectOption(@JsonProperty("value") String value,
@@ -1299,7 +1298,6 @@ public SessionConfigSelectOption(String value, String name) {
 	/**
 	 * Config option update - pushed by agent via session/update notification.
 	 */
-	@UnstableAcpApi
 	@JsonIgnoreProperties(ignoreUnknown = true)
 	@JsonInclude(JsonInclude.Include.NON_NULL)
 	public record ConfigOptionUpdate(@JsonProperty("sessionUpdate") String sessionUpdate,