diff --git a/internal/thinking/provider/openai/apply_test.go b/internal/thinking/provider/openai/apply_test.go
new file mode 100644
index 00000000000..437f9656ca3
--- /dev/null
+++ b/internal/thinking/provider/openai/apply_test.go
@@ -0,0 +1,33 @@
+package openai
+
+import (
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
+	"github.com/tidwall/gjson"
+)
+
+func TestApplyLevelFallbackAfterDisabledThinking(t *testing.T) {
+	model := &registry.ModelInfo{
+		ID: "openrouter-3o",
+		Thinking: &registry.ThinkingSupport{
+			Levels: []string{"max", "xhigh", "high", "medium", "low"},
+		},
+	}
+	config, err := thinking.ValidateConfig(
+		thinking.ThinkingConfig{Mode: thinking.ModeNone}, model, "claude", "openai", false,
+	)
+	if err != nil {
+		t.Fatalf("ValidateConfig() error = %v", err)
+	}
+	body, err := NewApplier().Apply(
+		[]byte(`{"messages":[{"role":"user","content":"hi"}]}`), *config, model,
+	)
+	if err != nil {
+		t.Fatalf("Apply() error = %v", err)
+	}
+	if got := gjson.GetBytes(body, "reasoning_effort").String(); got != "low" {
+		t.Fatalf("reasoning_effort = %q, want low; body=%s", got, body)
+	}
+}
diff --git a/internal/thinking/validate.go b/internal/thinking/validate.go
index 7e92a7710ce..32de67aec45 100644
--- a/internal/thinking/validate.go
+++ b/internal/thinking/validate.go
@@ -172,18 +172,30 @@ func ValidateConfig(config ThinkingConfig, modelInfo *registry.ModelInfo, fromFo
 		config.Budget = 0
 		config.Level = ""
 	} else {
-		switch config.Mode {
-		case ModeBudget, ModeAuto, ModeNone:
-			config.Budget = clampBudget(config.Budget, modelInfo, toFormat)
-		}
-
 		// ModeNone for a model that cannot be disabled falls back to the lowest
 		// supported level. Budget-capable models reach this path with Budget > 0;
 		// level-only models need the capability flags checked explicitly because
 		// their Min/Max range is zero.
 		cannotDisableLevelModel := !support.ZeroAllowed && !isLevelSupported(string(LevelNone), support.Levels)
-		if config.Mode == ModeNone && len(support.Levels) > 0 && (config.Budget > 0 || cannotDisableLevelModel) {
-			config.Level = ThinkingLevel(support.Levels[0])
+		pureLevelOnly := capability == CapabilityLevelOnly && support.Min == 0 && support.Max == 0
+		if config.Mode == ModeNone && pureLevelOnly {
+			// Level-only models have no numeric budget range, so do not pass their
+			// disabled sentinel through the numeric budget clamp. If the target
+			// cannot disable thinking, resolve its lowest supported level from the
+			// canonical order; provider metadata is not guaranteed to be sorted.
+			config.Budget = 0
+			if cannotDisableLevelModel {
+				config.Mode = ModeLevel
+				config.Level = clampLevel(LevelMinimal, modelInfo, toFormat)
+			}
+		} else {
+			switch config.Mode {
+			case ModeBudget, ModeAuto, ModeNone:
+				config.Budget = clampBudget(config.Budget, modelInfo, toFormat)
+			}
+			if config.Mode == ModeNone && len(support.Levels) > 0 && (config.Budget > 0 || cannotDisableLevelModel) {
+				config.Level = ThinkingLevel(support.Levels[0])
+			}
 		}
 	}
 
diff --git a/internal/thinking/validate_none_test.go b/internal/thinking/validate_none_test.go
new file mode 100644
index 00000000000..2873fb537df
--- /dev/null
+++ b/internal/thinking/validate_none_test.go
@@ -0,0 +1,84 @@
+package thinking
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
+	log "github.com/sirupsen/logrus"
+)
+
+func TestValidateConfigDisabledLevelOnlyUsesLowestWithoutBudgetWarning(t *testing.T) {
+	previousOutput := log.StandardLogger().Out
+	previousLevel := log.GetLevel()
+	var output bytes.Buffer
+	log.SetOutput(&output)
+	log.SetLevel(log.WarnLevel)
+	t.Cleanup(func() {
+		log.SetOutput(previousOutput)
+		log.SetLevel(previousLevel)
+	})
+
+	model := &registry.ModelInfo{
+		ID: "openrouter-3o",
+		Thinking: &registry.ThinkingSupport{
+			Levels: []string{"max", "xhigh", "high", "medium", "low"},
+		},
+	}
+	got, err := ValidateConfig(ThinkingConfig{Mode: ModeNone}, model, "claude", "openai", false)
+	if err != nil {
+		t.Fatalf("ValidateConfig() error = %v", err)
+	}
+	if got.Mode != ModeLevel || got.Budget != 0 || got.Level != LevelLow {
+		t.Fatalf("ValidateConfig() = %+v, want ModeLevel low with zero budget", got)
+	}
+	if strings.Contains(output.String(), "budget zero not allowed") {
+		t.Fatalf("disabled level-only thinking emitted a misleading warning: %s", output.String())
+	}
+}
+
+func TestValidateConfigDisabledHybridKeepsBudgetFallback(t *testing.T) {
+	model := &registry.ModelInfo{
+		ID: "hybrid-model",
+		Thinking: &registry.ThinkingSupport{
+			Min: 1024, Max: 32768, Levels: []string{"low", "high"},
+		},
+	}
+	got, err := ValidateConfig(ThinkingConfig{Mode: ModeNone}, model, "claude", "gemini", false)
+	if err != nil {
+		t.Fatalf("ValidateConfig() error = %v", err)
+	}
+	if got.Mode != ModeNone || got.Budget != 1024 || got.Level != LevelLow {
+		t.Fatalf("ValidateConfig() = %+v, want prior hybrid fallback budget 1024 and level low", got)
+	}
+}
+
+func TestValidateConfigDisabledLevelOnlyKeepsSupportedNoneWithoutBudgetWarning(t *testing.T) {
+	previousOutput := log.StandardLogger().Out
+	previousLevel := log.GetLevel()
+	var output bytes.Buffer
+	log.SetOutput(&output)
+	log.SetLevel(log.WarnLevel)
+	t.Cleanup(func() {
+		log.SetOutput(previousOutput)
+		log.SetLevel(previousLevel)
+	})
+
+	model := &registry.ModelInfo{
+		ID: "level-model-with-none",
+		Thinking: &registry.ThinkingSupport{
+			Levels: []string{"high", "none", "low"},
+		},
+	}
+	got, err := ValidateConfig(ThinkingConfig{Mode: ModeNone}, model, "claude", "openai", false)
+	if err != nil {
+		t.Fatalf("ValidateConfig() error = %v", err)
+	}
+	if got.Mode != ModeNone || got.Budget != 0 || got.Level != "" {
+		t.Fatalf("ValidateConfig() = %+v, want unchanged disabled mode", got)
+	}
+	if strings.Contains(output.String(), "budget zero not allowed") {
+		t.Fatalf("supported disabled thinking emitted a misleading warning: %s", output.String())
+	}
+}