diff --git a/relaykit/relayconvert/internal/oai_chat/to_gemini_chat_req_test.go b/relaykit/relayconvert/internal/oai_chat/to_gemini_chat_req_test.go
new file mode 100644
index 00000000000..a1691beb130
--- /dev/null
+++ b/relaykit/relayconvert/internal/oai_chat/to_gemini_chat_req_test.go
@@ -0,0 +1,41 @@
+package oaichat
+
+import (
+	"context"
+	"testing"
+
+	"github.com/QuantumNous/new-api/relaykit/dto"
+	"github.com/QuantumNous/new-api/relaykit/relayconvert/convmeta"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestOpenAIChatRequestToGeminiNormalizesNullableToolParameter(t *testing.T) {
+	got, err := OpenAIChatRequestToGeminiGenerateContent(context.Background(), dto.GeneralOpenAIRequest{
+		Model: "gemini-test",
+		Tools: []dto.ToolCallRequest{{
+			Type: "function",
+			Function: dto.FunctionRequest{
+				Name: "update_task",
+				Parameters: map[string]interface{}{
+					"type": "object",
+					"properties": map[string]interface{}{
+						"due_date": map[string]interface{}{
+							"anyOf": []interface{}{
+								map[string]interface{}{"type": "string"},
+								map[string]interface{}{"type": "null"},
+							},
+						},
+					},
+				},
+			},
+		}},
+	}, &convmeta.Values{})
+	require.NoError(t, err)
+
+	path := "0.functionDeclarations.0.parameters.properties.due_date"
+	assert.Equal(t, "STRING", gjson.GetBytes(got.Tools, path+".type").String())
+	assert.True(t, gjson.GetBytes(got.Tools, path+".nullable").Bool())
+	assert.False(t, gjson.GetBytes(got.Tools, path+".anyOf").Exists())
+}
diff --git a/relaykit/relayconvert/internal/oai_responses/to_gemini_chat_req_test.go b/relaykit/relayconvert/internal/oai_responses/to_gemini_chat_req_test.go
new file mode 100644
index 00000000000..029d77c6323
--- /dev/null
+++ b/relaykit/relayconvert/internal/oai_responses/to_gemini_chat_req_test.go
@@ -0,0 +1,27 @@
+package oairesponses
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	"github.com/QuantumNous/new-api/relaykit/dto"
+	"github.com/QuantumNous/new-api/relaykit/relayconvert/convmeta"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestOpenAIResponsesRequestToGeminiNormalizesLiteralToolUnion(t *testing.T) {
+	got, err := OpenAIResponsesRequestToGeminiChat(context.Background(), &dto.OpenAIResponsesRequest{
+		Model: "gemini-test",
+		Tools: json.RawMessage(`[{"type":"function","name":"update_task","parameters":{"type":"object","properties":{"status":{"anyOf":[{"type":"string","const":"open"},{"type":"string","const":"completed"}]}}}}]`),
+	}, &convmeta.Values{})
+	require.NoError(t, err)
+
+	path := "0.functionDeclarations.0.parameters.properties.status"
+	assert.Equal(t, "STRING", gjson.GetBytes(got.Tools, path+".type").String())
+	assert.Equal(t, "open", gjson.GetBytes(got.Tools, path+".enum.0").String())
+	assert.Equal(t, "completed", gjson.GetBytes(got.Tools, path+".enum.1").String())
+	assert.False(t, gjson.GetBytes(got.Tools, path+".anyOf").Exists())
+}
diff --git a/relaykit/relayconvert/internal/shared/gemini/schema.go b/relaykit/relayconvert/internal/shared/gemini/schema.go
index 75cc503473d..3c67e2ebba4 100644
--- a/relaykit/relayconvert/internal/shared/gemini/schema.go
+++ b/relaykit/relayconvert/internal/shared/gemini/schema.go
@@ -8,6 +8,7 @@ import (
 
 var geminiOpenAPISchemaAllowedFields = map[string]struct{}{
 	"anyOf":            {},
+	"const":            {},
 	"default":          {},
 	"description":      {},
 	"enum":             {},
@@ -80,6 +81,10 @@ func cleanGeminiFunctionParametersWithDepth(params interface{}, depth int) inter
 			cleanedMap["anyOf"] = cleanedNested
 		}
 
+		normalizeGeminiSchemaConst(cleanedMap)
+		normalizeGeminiSchemaAnyOf(cleanedMap)
+		delete(cleanedMap, "const")
+
 		return cleanedMap
 	case []interface{}:
 		cleanedArray := make([]interface{}, len(v))
@@ -102,9 +107,11 @@ func cleanGeminiFunctionParametersShallow(params interface{}) interface{} {
 			}
 		}
 		normalizeGeminiSchemaTypeAndNullable(cleanedMap)
+		normalizeGeminiSchemaConst(cleanedMap)
 		delete(cleanedMap, "properties")
 		delete(cleanedMap, "items")
 		delete(cleanedMap, "anyOf")
+		delete(cleanedMap, "const")
 		return cleanedMap
 	case []interface{}:
 		return []interface{}{}
@@ -113,6 +120,114 @@ func cleanGeminiFunctionParametersShallow(params interface{}) interface{} {
 	}
 }
 
+func normalizeGeminiSchemaConst(schema map[string]interface{}) {
+	constValue, ok := schema["const"]
+	if !ok {
+		return
+	}
+	if _, hasEnum := schema["enum"]; !hasEnum {
+		schema["enum"] = []interface{}{constValue}
+	}
+}
+
+func normalizeGeminiSchemaAnyOf(schema map[string]interface{}) {
+	branches, ok := schema["anyOf"].([]interface{})
+	if !ok || len(branches) == 0 {
+		return
+	}
+
+	concreteBranches := make([]map[string]interface{}, 0, len(branches))
+	nullable := false
+	for _, branch := range branches {
+		branchSchema, ok := branch.(map[string]interface{})
+		if !ok {
+			return
+		}
+		if isGeminiNullSchema(branchSchema) {
+			nullable = true
+			continue
+		}
+		concreteBranches = append(concreteBranches, branchSchema)
+	}
+
+	if len(concreteBranches) == 1 && nullable {
+		mergeGeminiSchema(schema, concreteBranches[0])
+		schema["nullable"] = true
+		delete(schema, "anyOf")
+		return
+	}
+
+	commonType, sameType := commonGeminiSchemaType(concreteBranches)
+	if sameType {
+		if _, hasType := schema["type"]; !hasType {
+			schema["type"] = commonType
+		}
+	}
+	if nullable {
+		schema["nullable"] = true
+	}
+
+	values, enumOnly := geminiEnumUnionValues(concreteBranches)
+	if sameType && enumOnly {
+		schema["enum"] = values
+		delete(schema, "anyOf")
+	}
+}
+
+func isGeminiNullSchema(schema map[string]interface{}) bool {
+	if nullable, ok := schema["nullable"].(bool); !ok || !nullable {
+		return false
+	}
+	for key := range schema {
+		if key != "nullable" {
+			return false
+		}
+	}
+	return true
+}
+
+func mergeGeminiSchema(target map[string]interface{}, source map[string]interface{}) {
+	for key, value := range source {
+		if _, exists := target[key]; !exists {
+			target[key] = value
+		}
+	}
+}
+
+func commonGeminiSchemaType(branches []map[string]interface{}) (string, bool) {
+	if len(branches) == 0 {
+		return "", false
+	}
+	commonType, ok := branches[0]["type"].(string)
+	if !ok || commonType == "" {
+		return "", false
+	}
+	for _, branch := range branches[1:] {
+		branchType, ok := branch["type"].(string)
+		if !ok || branchType != commonType {
+			return "", false
+		}
+	}
+	return commonType, true
+}
+
+func geminiEnumUnionValues(branches []map[string]interface{}) ([]interface{}, bool) {
+	values := make([]interface{}, 0, len(branches))
+	for _, branch := range branches {
+		for key := range branch {
+			if key != "type" && key != "enum" {
+				return nil, false
+			}
+		}
+		branchValues, ok := branch["enum"].([]interface{})
+		if !ok || len(branchValues) == 0 {
+			return nil, false
+		}
+		values = append(values, branchValues...)
+	}
+	return values, true
+}
+
 func normalizeGeminiSchemaTypeAndNullable(schema map[string]interface{}) {
 	rawType, ok := schema["type"]
 	if !ok || rawType == nil {
diff --git a/relaykit/relayconvert/internal/shared/gemini/schema_test.go b/relaykit/relayconvert/internal/shared/gemini/schema_test.go
new file mode 100644
index 00000000000..9c939b28234
--- /dev/null
+++ b/relaykit/relayconvert/internal/shared/gemini/schema_test.go
@@ -0,0 +1,53 @@
+package gemini
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCleanFunctionParametersNormalizesNullableUnion(t *testing.T) {
+	cleaned := CleanFunctionParameters(map[string]interface{}{
+		"type": "object",
+		"properties": map[string]interface{}{
+			"due_date": map[string]interface{}{
+				"description": "Optional due date",
+				"anyOf": []interface{}{
+					map[string]interface{}{"type": "string"},
+					map[string]interface{}{"type": "null"},
+				},
+			},
+		},
+	})
+
+	root, ok := cleaned.(map[string]interface{})
+	require.True(t, ok)
+	properties, ok := root["properties"].(map[string]interface{})
+	require.True(t, ok)
+	dueDate, ok := properties["due_date"].(map[string]interface{})
+	require.True(t, ok)
+
+	assert.Equal(t, "OBJECT", root["type"])
+	assert.Equal(t, "STRING", dueDate["type"])
+	assert.Equal(t, true, dueDate["nullable"])
+	assert.Equal(t, "Optional due date", dueDate["description"])
+	assert.NotContains(t, dueDate, "anyOf")
+}
+
+func TestCleanFunctionParametersNormalizesLiteralUnion(t *testing.T) {
+	cleaned := CleanFunctionParameters(map[string]interface{}{
+		"anyOf": []interface{}{
+			map[string]interface{}{"type": "string", "const": "open"},
+			map[string]interface{}{"type": "string", "const": "completed"},
+		},
+	})
+
+	schema, ok := cleaned.(map[string]interface{})
+	require.True(t, ok)
+
+	assert.Equal(t, "STRING", schema["type"])
+	assert.Equal(t, []interface{}{"open", "completed"}, schema["enum"])
+	assert.NotContains(t, schema, "anyOf")
+	assert.NotContains(t, schema, "const")
+}