diff --git a/internal/runtime/executor/claude_device_profile.go b/internal/runtime/executor/claude_device_profile.go
index 9de3689f..44d7069d 100644
--- a/internal/runtime/executor/claude_device_profile.go
+++ b/internal/runtime/executor/claude_device_profile.go
@@ -158,6 +158,19 @@ func parseClaudeCLIVersion(userAgent string) (claudeCLIVersion, bool) {
 	return claudeCLIVersion{major: major, minor: minor, patch: patch}, true
 }
 
+func shouldUpgradeClaudeDeviceProfile(candidate, current claudeDeviceProfile) bool {
+	if candidate.UserAgent == "" {
+		return false
+	}
+	if current.UserAgent == "" {
+		return true
+	}
+	if current.Version == (claudeCLIVersion{}) {
+		return false
+	}
+	return candidate.Version.Compare(current.Version) > 0
+}
+
 func extractClaudeDeviceProfile(headers http.Header, cfg *config.Config) (claudeDeviceProfile, bool) {
 	if headers == nil {
 		return claudeDeviceProfile{}, false
@@ -235,13 +248,16 @@ func resolveClaudeDeviceProfile(auth *cliproxyauth.Auth, apiKey string, headers
 	now := time.Now()
 	baseline := defaultClaudeDeviceProfile(cfg)
 	candidate, hasCandidate := extractClaudeDeviceProfile(headers, cfg)
+	if hasCandidate && !shouldUpgradeClaudeDeviceProfile(candidate, baseline) {
+		hasCandidate = false
+	}
 
 	claudeDeviceProfileCacheMu.RLock()
 	entry, hasCached := claudeDeviceProfileCache[cacheKey]
 	cachedValid := hasCached && entry.expire.After(now) && entry.profile.UserAgent != ""
 	claudeDeviceProfileCacheMu.RUnlock()
 
-	if hasCandidate && (!cachedValid || candidate.Version.Compare(entry.profile.Version) > 0) {
+	if hasCandidate && (!cachedValid || shouldUpgradeClaudeDeviceProfile(candidate, entry.profile)) {
 		newEntry := claudeDeviceProfileCacheEntry{
 			profile: candidate,
 			expire:  now.Add(claudeDeviceProfileTTL),
diff --git a/internal/runtime/executor/claude_executor_test.go b/internal/runtime/executor/claude_executor_test.go
index 3ff8fd7b..e73b1c06 100644
--- a/internal/runtime/executor/claude_executor_test.go
+++ b/internal/runtime/executor/claude_executor_test.go
@@ -164,6 +164,48 @@ func TestApplyClaudeHeaders_TracksHighestClaudeCLIFingerprint(t *testing.T) {
 	assertClaudeFingerprint(t, lowerReq.Header, "claude-cli/2.1.63 (external, cli)", "0.75.0", "v24.4.0", "MacOS", "arm64")
 }
 
+func TestApplyClaudeHeaders_DoesNotDowngradeConfiguredBaselineOnFirstClaudeClient(t *testing.T) {
+	resetClaudeDeviceProfileCache()
+	stabilize := true
+
+	cfg := &config.Config{
+		ClaudeHeaderDefaults: config.ClaudeHeaderDefaults{
+			UserAgent:              "claude-cli/2.1.70 (external, cli)",
+			PackageVersion:         "0.80.0",
+			RuntimeVersion:         "v24.5.0",
+			OS:                     "MacOS",
+			Arch:                   "arm64",
+			StabilizeDeviceProfile: &stabilize,
+		},
+	}
+	auth := &cliproxyauth.Auth{
+		ID: "auth-baseline-floor",
+		Attributes: map[string]string{
+			"api_key": "key-baseline-floor",
+		},
+	}
+
+	olderClaudeReq := newClaudeHeaderTestRequest(t, http.Header{
+		"User-Agent":                  []string{"claude-cli/2.1.62 (external, cli)"},
+		"X-Stainless-Package-Version": []string{"0.74.0"},
+		"X-Stainless-Runtime-Version": []string{"v24.3.0"},
+		"X-Stainless-Os":              []string{"Linux"},
+		"X-Stainless-Arch":            []string{"x64"},
+	})
+	applyClaudeHeaders(olderClaudeReq, auth, "key-baseline-floor", false, nil, cfg)
+	assertClaudeFingerprint(t, olderClaudeReq.Header, "claude-cli/2.1.70 (external, cli)", "0.80.0", "v24.5.0", "MacOS", "arm64")
+
+	newerClaudeReq := newClaudeHeaderTestRequest(t, http.Header{
+		"User-Agent":                  []string{"claude-cli/2.1.71 (external, cli)"},
+		"X-Stainless-Package-Version": []string{"0.81.0"},
+		"X-Stainless-Runtime-Version": []string{"v24.6.0"},
+		"X-Stainless-Os":              []string{"Linux"},
+		"X-Stainless-Arch":            []string{"x64"},
+	})
+	applyClaudeHeaders(newerClaudeReq, auth, "key-baseline-floor", false, nil, cfg)
+	assertClaudeFingerprint(t, newerClaudeReq.Header, "claude-cli/2.1.71 (external, cli)", "0.81.0", "v24.6.0", "Linux", "x64")
+}
+
 func TestApplyClaudeHeaders_DisableDeviceProfileStabilization(t *testing.T) {
 	resetClaudeDeviceProfileCache()