diff --git a/openai.go b/openai.go
index dc3abc8..d1cd543 100644
--- a/openai.go
+++ b/openai.go
@@ -15,13 +15,18 @@ import (
 type ChatCompletionNewParamsWrapper struct {
 	openai.ChatCompletionNewParams `json:""`
 	Stream                         bool `json:"stream,omitempty"`
+	MaxCompletionTokens            *int `json:"max_completion_tokens,omitempty"`
 }
 
 func (c ChatCompletionNewParamsWrapper) MarshalJSON() ([]byte, error) {
 	type shadow ChatCompletionNewParamsWrapper
-	return param.MarshalWithExtras(c, (*shadow)(&c), map[string]any{
+	extras := map[string]any{
 		"stream": c.Stream,
-	})
+	}
+	if c.MaxCompletionTokens != nil {
+		extras["max_completion_tokens"] = *c.MaxCompletionTokens
+	}
+	return param.MarshalWithExtras(c, (*shadow)(&c), extras)
 }
 
 func (c *ChatCompletionNewParamsWrapper) UnmarshalJSON(raw []byte) error {
@@ -43,6 +48,33 @@ func (c *ChatCompletionNewParamsWrapper) UnmarshalJSON(raw []byte) error {
 		c.ChatCompletionNewParams.StreamOptions = openai.ChatCompletionStreamOptionsParam{}
 	}
 
+	// Extract max_completion_tokens if present and positive
+	// OpenAI API requires positive integers for token limits
+	var data map[string]any
+	if err := json.Unmarshal(raw, &data); err == nil {
+		if val, exists := data["max_completion_tokens"]; exists {
+			// Field is explicitly set, convert to int
+			var tokens int
+			switch v := val.(type) {
+			case float64:
+				tokens = int(v)
+			case int:
+				tokens = v
+			case int64:
+				tokens = int(v)
+			default:
+				// Invalid type, skip
+				return nil
+			}
+			// Only set if positive (0 and negative values are invalid)
+			if tokens > 0 {
+				c.MaxCompletionTokens = &tokens
+				// Set it in the underlying params as well
+				c.ChatCompletionNewParams.MaxCompletionTokens = openai.Int(int64(tokens))
+			}
+		}
+	}
+
 	return nil
 }
 
diff --git a/openai_test.go b/openai_test.go
index 35e52f2..b4a954a 100644
--- a/openai_test.go
+++ b/openai_test.go
@@ -1,6 +1,7 @@
 package aibridge_test
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/coder/aibridge"
@@ -131,3 +132,88 @@ func TestOpenAILastUserPrompt(t *testing.T) {
 		})
 	}
 }
+
+func TestMaxCompletionTokens(t *testing.T) {
+	t.Parallel()
+
+	t.Run("unmarshal max_completion_tokens from JSON", func(t *testing.T) {
+		jsonStr := `{
+			"model": "gpt-4o",
+			"messages": [{"role": "user", "content": "Hello"}],
+			"max_completion_tokens": 1024
+		}`
+
+		var wrapper aibridge.ChatCompletionNewParamsWrapper
+		err := json.Unmarshal([]byte(jsonStr), &wrapper)
+		require.NoError(t, err)
+		require.NotNil(t, wrapper.MaxCompletionTokens)
+		require.Equal(t, 1024, *wrapper.MaxCompletionTokens)
+	})
+
+	t.Run("unmarshal max_completion_tokens with zero value ignored", func(t *testing.T) {
+		jsonStr := `{
+			"model": "gpt-4o",
+			"messages": [{"role": "user", "content": "Hello"}],
+			"max_completion_tokens": 0
+		}`
+
+		var wrapper aibridge.ChatCompletionNewParamsWrapper
+		err := json.Unmarshal([]byte(jsonStr), &wrapper)
+		require.NoError(t, err)
+		require.Nil(t, wrapper.MaxCompletionTokens, "max_completion_tokens should not be set when 0 (invalid value)")
+	})
+
+	t.Run("unmarshal max_completion_tokens with negative value ignored", func(t *testing.T) {
+		jsonStr := `{
+			"model": "gpt-4o",
+			"messages": [{"role": "user", "content": "Hello"}],
+			"max_completion_tokens": -100
+		}`
+
+		var wrapper aibridge.ChatCompletionNewParamsWrapper
+		err := json.Unmarshal([]byte(jsonStr), &wrapper)
+		require.NoError(t, err)
+		require.Nil(t, wrapper.MaxCompletionTokens, "max_completion_tokens should not be set when negative (invalid value)")
+	})
+
+	t.Run("marshal max_completion_tokens to JSON", func(t *testing.T) {
+		maxTokens := 2048
+		wrapper := aibridge.ChatCompletionNewParamsWrapper{
+			ChatCompletionNewParams: openai.ChatCompletionNewParams{
+				Model: openai.ChatModelGPT4o,
+				Messages: []openai.ChatCompletionMessageParamUnion{
+					openai.UserMessage("Hello"),
+				},
+			},
+			MaxCompletionTokens: &maxTokens,
+		}
+
+		jsonBytes, err := json.Marshal(wrapper)
+		require.NoError(t, err)
+
+		var result map[string]interface{}
+		err = json.Unmarshal(jsonBytes, &result)
+		require.NoError(t, err)
+		require.Equal(t, float64(2048), result["max_completion_tokens"])
+	})
+
+	t.Run("max_completion_tokens not set when nil", func(t *testing.T) {
+		wrapper := aibridge.ChatCompletionNewParamsWrapper{
+			ChatCompletionNewParams: openai.ChatCompletionNewParams{
+				Model: openai.ChatModelGPT4o,
+				Messages: []openai.ChatCompletionMessageParamUnion{
+					openai.UserMessage("Hello"),
+				},
+			},
+		}
+
+		jsonBytes, err := json.Marshal(wrapper)
+		require.NoError(t, err)
+
+		var result map[string]interface{}
+		err = json.Unmarshal(jsonBytes, &result)
+		require.NoError(t, err)
+		_, exists := result["max_completion_tokens"]
+		require.False(t, exists, "max_completion_tokens should not be present when nil")
+	})
+}