diff --git a/agentenv/agentenv.go b/agentenv/agentenv.go
index f1f36c1..0bd53eb 100644
--- a/agentenv/agentenv.go
+++ b/agentenv/agentenv.go
@@ -12,7 +12,7 @@ type agentSource struct {
 }
 
 var sources = []agentSource{
-	{"CLAUDE_CODE", "claude-code"},
+	{"CLAUDECODE", "claude-code"},
 	{"ANTIGRAVITY_AGENT", "antigravity"},
 	{"AI_AGENT", ""},
 	{"LLM_AGENT", ""},
diff --git a/agentenv/agentenv_test.go b/agentenv/agentenv_test.go
index 5077319..4f438d5 100644
--- a/agentenv/agentenv_test.go
+++ b/agentenv/agentenv_test.go
@@ -8,7 +8,7 @@ func TestDetected(t *testing.T) {
 	// Every env var Detected looks at. Each subtest zeroes all of them first
 	// so it's isolated from whatever environment its running in (e.g. running
 	// inside an AI agent, or a local dev machine) has set.
-	knownVars := []string{"CLAUDE_CODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"}
+	knownVars := []string{"CLAUDECODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"}
 
 	tests := []struct {
 		name string
@@ -22,7 +22,7 @@ func TestDetected(t *testing.T) {
 		},
 		{
 			name: "claude code, branded slug regardless of value",
-			env:  map[string]string{"CLAUDE_CODE": "1"},
+			env:  map[string]string{"CLAUDECODE": "1"},
 			want: "claude-code",
 		},
 		{
@@ -38,12 +38,12 @@ func TestDetected(t *testing.T) {
 		{
 			// tricky scenario, decision for branded
 			name: "branded wins over generic (precedence)",
-			env:  map[string]string{"CLAUDE_CODE": "1", "AI_AGENT": "cursor"},
+			env:  map[string]string{"CLAUDECODE": "1", "AI_AGENT": "cursor"},
 			want: "claude-code",
 		},
 		{
 			name: "empty string treated as unset",
-			env:  map[string]string{"CLAUDE_CODE": ""},
+			env:  map[string]string{"CLAUDECODE": ""},
 			want: "",
 		},
 		{
diff --git a/client/client_test.go b/client/client_test.go
index 48b9057..a390168 100644
--- a/client/client_test.go
+++ b/client/client_test.go
@@ -56,7 +56,7 @@ func TestFormatBatchErrorBody(t *testing.T) {
 	}
 }
 func TestComposeUserAgent(t *testing.T) {
-	knownVars := []string{"CLAUDE_CODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"}
+	knownVars := []string{"CLAUDECODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"}
 
 	tests := []struct {
 		name     string
@@ -77,7 +77,7 @@ func TestComposeUserAgent(t *testing.T) {
 		{
 			name:     "agent and skill together",
 			skill:    "cli-command-create",
-			agentEnv: map[string]string{"CLAUDE_CODE": "1"},
+			agentEnv: map[string]string{"CLAUDECODE": "1"},
 			want:     "prolific-oss/cli/" + version.Get() + " agent/claude-code skill/cli-command-create",
 		},
 		{
@@ -105,7 +105,7 @@ func TestComposeUserAgent(t *testing.T) {
 
 func TestExecuteSetsSkillInUserAgent(t *testing.T) {
 	// Isolate from ambient agent env vars (this shell has AI_AGENT set).
-	for _, k := range []string{"CLAUDE_CODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"} {
+	for _, k := range []string{"CLAUDECODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"} {
 		t.Setenv(k, "")
 	}
 
@@ -134,10 +134,10 @@ func TestExecuteSetsSkillInUserAgent(t *testing.T) {
 
 func TestExecuteSetsAgentInUserAgent(t *testing.T) {
 	// Isolate from ambient agent env vars (this shell has AI_AGENT set).
-	for _, k := range []string{"CLAUDE_CODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"} {
+	for _, k := range []string{"CLAUDECODE", "ANTIGRAVITY_AGENT", "AI_AGENT", "LLM_AGENT"} {
 		t.Setenv(k, "")
 	}
-	t.Setenv("CLAUDE_CODE", "1")
+	t.Setenv("CLAUDECODE", "1")
 
 	var gotUserAgent string
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {