diff --git a/crates/buzz-acp/src/acp.rs b/crates/buzz-acp/src/acp.rs
index 93109fa94d..c4082d02f7 100644
--- a/crates/buzz-acp/src/acp.rs
+++ b/crates/buzz-acp/src/acp.rs
@@ -2970,28 +2970,51 @@ mod tests {
     #[cfg(unix)]
     #[tokio::test]
     async fn spawn_applies_runtime_env_defaults_with_extra_env_precedence() {
-        const VAR: &str = "HERMES_ACP_SKIP_CONFIGURED_MCP";
-        if std::env::var_os(VAR).is_some() {
+        const HERMES_VAR: &str = "HERMES_ACP_SKIP_CONFIGURED_MCP";
+        const CLAUDE_VAR: &str = "CLAUDE_CODE_AUTO_COMPACT_WINDOW";
+        if std::env::var_os(HERMES_VAR).is_some() || std::env::var_os(CLAUDE_VAR).is_some() {
             // Inherited parent values win over both layers; the default and
             // override behavior below is unobservable in such an environment.
             return;
         }
 
         assert_eq!(
-            spawn_named_and_read_child_env("hermes-acp", VAR, &[]).await,
+            spawn_named_and_read_child_env("hermes-acp", HERMES_VAR, &[]).await,
             "1",
-            "Hermes spawns must default {VAR}=1"
+            "Hermes spawns must default {HERMES_VAR}=1"
         );
         assert_eq!(
-            spawn_named_and_read_child_env("hermes-acp", VAR, &[(VAR.into(), "0".into())]).await,
+            spawn_named_and_read_child_env(
+                "hermes-acp",
+                HERMES_VAR,
+                &[(HERMES_VAR.into(), "0".into())]
+            )
+            .await,
             "0",
             "an explicit extra_env entry must override the runtime default"
         );
         assert_eq!(
-            spawn_named_and_read_child_env("other-agent", VAR, &[]).await,
-            "<unset>",
-            "non-Hermes spawns must not receive Hermes defaults"
+            spawn_named_and_read_child_env("claude-agent-acp", CLAUDE_VAR, &[]).await,
+            "200000",
+            "Claude spawns must default {CLAUDE_VAR}=200000"
         );
+        assert_eq!(
+            spawn_named_and_read_child_env(
+                "claude-agent-acp",
+                CLAUDE_VAR,
+                &[(CLAUDE_VAR.into(), "300000".into())]
+            )
+            .await,
+            "300000",
+            "an explicit extra_env entry must override the runtime default"
+        );
+        for agent in ["goose", "codex-acp", "other-agent"] {
+            assert_eq!(
+                spawn_named_and_read_child_env(agent, CLAUDE_VAR, &[]).await,
+                "<unset>",
+                "non-Claude spawn {agent} must not receive Claude defaults"
+            );
+        }
     }
 
     #[tokio::test]
diff --git a/crates/buzz-acp/src/config.rs b/crates/buzz-acp/src/config.rs
index d959685846..38b0b774ce 100644
--- a/crates/buzz-acp/src/config.rs
+++ b/crates/buzz-acp/src/config.rs
@@ -712,9 +712,17 @@ fn default_agent_args(command: &str) -> Option<Vec<String>> {
 /// startup budget (see block/buzz#3355). Skip that unrelated global startup
 /// by default; an operator or persona can still opt back in by setting the
 /// variable explicitly.
+///
+/// Claude: set a 200,000-token automatic-compaction window for Buzz-owned
+/// children only. Claude Code caps this to the selected model's context
+/// capacity. An inherited parent value or explicit persona value wins, so an
+/// operator can select a different window without modifying Claude settings.
 pub(crate) fn default_agent_env(command: &str) -> &'static [(&'static str, &'static str)] {
     match normalize_agent_command_identity(command).as_str() {
         "hermes" | "hermes-agent" | "hermes-acp" => &[("HERMES_ACP_SKIP_CONFIGURED_MCP", "1")],
+        "claude-agent-acp" | "claude-code-acp" | "claude-code" | "claudecode" => {
+            &[("CLAUDE_CODE_AUTO_COMPACT_WINDOW", "200000")]
+        }
         _ => &[],
     }
 }
@@ -1635,7 +1643,7 @@ mod tests {
     }
 
     #[test]
-    fn default_agent_env_recognizes_hermes_identities() {
+    fn default_agent_env_recognizes_runtime_identities() {
         for command in [
             "hermes",
             "hermes-agent",
@@ -1650,10 +1658,24 @@ mod tests {
                 "unexpected env defaults for {command}"
             );
         }
-        for command in ["goose", "codex-acp", "claude-agent-acp", "buzz-agent", ""] {
+        for command in [
+            "claude-agent-acp",
+            "claude-code-acp",
+            "claude-code",
+            "claudecode",
+            "/opt/claude/bin/claude-agent-acp",
+            r"C:\Users\test\AppData\Roaming\npm\CLAUDE-CODE-ACP.cmd",
+        ] {
+            assert_eq!(
+                default_agent_env(command),
+                &[("CLAUDE_CODE_AUTO_COMPACT_WINDOW", "200000")],
+                "unexpected env defaults for {command}"
+            );
+        }
+        for command in ["goose", "codex-acp", "buzz-agent", ""] {
             assert!(
                 default_agent_env(command).is_empty(),
-                "non-Hermes command must have no env defaults: {command}"
+                "unrecognized command must have no env defaults: {command}"
             );
         }
     }