diff --git a/chat_stream_test.go b/chat_stream_test.go
index 4d992e4..eabb0f3 100644
--- a/chat_stream_test.go
+++ b/chat_stream_test.go
@@ -959,6 +959,56 @@ func TestCreateChatCompletionStreamReasoningValidatorFails(t *testing.T) {
 	}
 }
 
+func TestCreateChatCompletionStreamO3ReasoningValidatorFails(t *testing.T) {
+	client, _, _ := setupOpenAITestServer()
+
+	stream, err := client.CreateChatCompletionStream(context.Background(), openai.ChatCompletionRequest{
+		MaxTokens: 100, // This will trigger the validator to fail
+		Model:     openai.O3,
+		Messages: []openai.ChatCompletionMessage{
+			{
+				Role:    openai.ChatMessageRoleUser,
+				Content: "Hello!",
+			},
+		},
+		Stream: true,
+	})
+
+	if stream != nil {
+		t.Error("Expected nil stream when validation fails")
+		stream.Close()
+	}
+
+	if !errors.Is(err, openai.ErrReasoningModelMaxTokensDeprecated) {
+		t.Errorf("Expected ErrReasoningModelMaxTokensDeprecated for O3, got: %v", err)
+	}
+}
+
+func TestCreateChatCompletionStreamO4MiniReasoningValidatorFails(t *testing.T) {
+	client, _, _ := setupOpenAITestServer()
+
+	stream, err := client.CreateChatCompletionStream(context.Background(), openai.ChatCompletionRequest{
+		MaxTokens: 100, // This will trigger the validator to fail
+		Model:     openai.O4Mini,
+		Messages: []openai.ChatCompletionMessage{
+			{
+				Role:    openai.ChatMessageRoleUser,
+				Content: "Hello!",
+			},
+		},
+		Stream: true,
+	})
+
+	if stream != nil {
+		t.Error("Expected nil stream when validation fails")
+		stream.Close()
+	}
+
+	if !errors.Is(err, openai.ErrReasoningModelMaxTokensDeprecated) {
+		t.Errorf("Expected ErrReasoningModelMaxTokensDeprecated for O4Mini, got: %v", err)
+	}
+}
+
 func compareChatStreamResponseChoices(c1, c2 openai.ChatCompletionStreamChoice) bool {
 	if c1.Index != c2.Index {
 		return false
diff --git a/completion.go b/completion.go
index 0d0c1a8..7a6de30 100644
--- a/completion.go
+++ b/completion.go
@@ -16,8 +16,12 @@ const (
 	O1Preview20240912       = "o1-preview-2024-09-12"
 	O1                      = "o1"
 	O120241217              = "o1-2024-12-17"
+	O3                      = "o3"
+	O320250416              = "o3-2025-04-16"
 	O3Mini                  = "o3-mini"
 	O3Mini20250131          = "o3-mini-2025-01-31"
+	O4Mini                  = "o4-mini"
+	O4Mini2020416           = "o4-mini-2025-04-16"
 	GPT432K0613             = "gpt-4-32k-0613"
 	GPT432K0314             = "gpt-4-32k-0314"
 	GPT432K                 = "gpt-4-32k"
@@ -99,6 +103,10 @@ var disabledModelsForEndpoints = map[string]map[string]bool{
 		O1Preview20240912:       true,
 		O3Mini:                  true,
 		O3Mini20250131:          true,
+		O4Mini:                  true,
+		O4Mini2020416:           true,
+		O3:                      true,
+		O320250416:              true,
 		GPT3Dot5Turbo:           true,
 		GPT3Dot5Turbo0301:       true,
 		GPT3Dot5Turbo0613:       true,
diff --git a/completion_test.go b/completion_test.go
index 83bd899..27e2d15 100644
--- a/completion_test.go
+++ b/completion_test.go
@@ -33,6 +33,42 @@ func TestCompletionsWrongModel(t *testing.T) {
 	}
 }
 
+// TestCompletionsWrongModelO3 Tests the completions endpoint with O3 model which is not supported.
+func TestCompletionsWrongModelO3(t *testing.T) {
+	config := openai.DefaultConfig("whatever")
+	config.BaseURL = "http://localhost/v1"
+	client := openai.NewClientWithConfig(config)
+
+	_, err := client.CreateCompletion(
+		context.Background(),
+		openai.CompletionRequest{
+			MaxTokens: 5,
+			Model:     openai.O3,
+		},
+	)
+	if !errors.Is(err, openai.ErrCompletionUnsupportedModel) {
+		t.Fatalf("CreateCompletion should return ErrCompletionUnsupportedModel for O3, but returned: %v", err)
+	}
+}
+
+// TestCompletionsWrongModelO4Mini Tests the completions endpoint with O4Mini model which is not supported.
+func TestCompletionsWrongModelO4Mini(t *testing.T) {
+	config := openai.DefaultConfig("whatever")
+	config.BaseURL = "http://localhost/v1"
+	client := openai.NewClientWithConfig(config)
+
+	_, err := client.CreateCompletion(
+		context.Background(),
+		openai.CompletionRequest{
+			MaxTokens: 5,
+			Model:     openai.O4Mini,
+		},
+	)
+	if !errors.Is(err, openai.ErrCompletionUnsupportedModel) {
+		t.Fatalf("CreateCompletion should return ErrCompletionUnsupportedModel for O4Mini, but returned: %v", err)
+	}
+}
+
 func TestCompletionWithStream(t *testing.T) {
 	config := openai.DefaultConfig("whatever")
 	client := openai.NewClientWithConfig(config)
diff --git a/models_test.go b/models_test.go
index 24a28ed..7fd010c 100644
--- a/models_test.go
+++ b/models_test.go
@@ -47,6 +47,24 @@ func TestGetModel(t *testing.T) {
 	checks.NoError(t, err, "GetModel error")
 }
 
+// TestGetModelO3 Tests the retrieve O3 model endpoint of the API using the mocked server.
+func TestGetModelO3(t *testing.T) {
+	client, server, teardown := setupOpenAITestServer()
+	defer teardown()
+	server.RegisterHandler("/v1/models/o3", handleGetModelEndpoint)
+	_, err := client.GetModel(context.Background(), "o3")
+	checks.NoError(t, err, "GetModel error for O3")
+}
+
+// TestGetModelO4Mini Tests the retrieve O4Mini model endpoint of the API using the mocked server.
+func TestGetModelO4Mini(t *testing.T) {
+	client, server, teardown := setupOpenAITestServer()
+	defer teardown()
+	server.RegisterHandler("/v1/models/o4-mini", handleGetModelEndpoint)
+	_, err := client.GetModel(context.Background(), "o4-mini")
+	checks.NoError(t, err, "GetModel error for O4Mini")
+}
+
 func TestAzureGetModel(t *testing.T) {
 	client, server, teardown := setupAzureTestServer()
 	defer teardown()
diff --git a/reasoning_validator.go b/reasoning_validator.go
index 040d6b4..2910b13 100644
--- a/reasoning_validator.go
+++ b/reasoning_validator.go
@@ -40,8 +40,9 @@ func NewReasoningValidator() *ReasoningValidator {
 func (v *ReasoningValidator) Validate(request ChatCompletionRequest) error {
 	o1Series := strings.HasPrefix(request.Model, "o1")
 	o3Series := strings.HasPrefix(request.Model, "o3")
+	o4Series := strings.HasPrefix(request.Model, "o4")
 
-	if !o1Series && !o3Series {
+	if !o1Series && !o3Series && !o4Series {
 		return nil
 	}