Can't turn off thinking mode using Gemma4

Hi ,
I’m calling the gemma4 model both gemma-4-31b-it and gemma-4-26b-a4b-it via rest api and I can’t runoff thinking.
this is my url https://generativelanguage.googleapis.com/v1beta/models/gemma-4-31b-it:streamGenerateContent?key=33333333

and here is the body

{

"contents": \[

           

  {

    "role": "user",

    "parts": \[

      {

        "text": "Who are you"

      }

    \]

  }

\],

"generationConfig": {

     

    "maxOutputTokens": 4048,

    "responseMimeType": "application/json",

    "frequencyPenalty": 0.0,

    "presencePenalty": 0.0,

    "temperature": 0.0  ,

    "topP": 1

},



"systemInstruction": {

"parts": \[

  {     

    "text": "You are a AI assistant."

  }

\]

}

}
here are the results
[

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "\*   User asks: \\"Who are you\\"\\n    \*   ",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 24,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 14

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "Constraint: Generate only a valid, parseable JSON.\\n    \*   Constraint: No comments inside JSON.\\n    ",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 48,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 38

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "\*   Constraint: No extra text outside JSON.\\n    \*   Constraint: If multiple, return a single array.",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 72,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 62

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "\\n\\n    \*   Identity: AI assistant.\\n    \*   Role: Helpful, informative, and versatile.\\n\\n    ",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 96,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 86

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "\*   Option 1: \`{\\"answer\\": \\"I am an AI assistant.\\"}\`\\n    \*   Option ",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 120,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 110

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "2: \`{\\"identity\\": \\"AI Assistant\\", \\"description\\": \\"A large language model trained by Google.\\"}\`\\n\\n",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 144,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 134

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "    \*   Valid JSON? Yes.\\n    \*   Double-quoted strings? Yes.\\n    \*   No",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 168,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 158

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": " comments? Yes.\\n    \*   No extra text? Yes.",

                        "thought": **true**

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "totalTokenCount": 182,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 172

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "{\\n  \\"identity\\": \\"AI assistant"

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "candidatesTokenCount": 9,

        "totalTokenCount": 191,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 172

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": "\\",\\n  \\"description\\": \\"A large language model trained by Google.\\"\\n}"

                    }

                \],

                "role": "model"

            },

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "candidatesTokenCount": 26,

        "totalTokenCount": 208,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 172

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

},

{

    "candidates": \[

        {

            "content": {

                "parts": \[

                    {

                        "text": ""

                    }

                \],

                "role": "model"

            },

            "finishReason": "STOP",

            "index": 0

        }

    \],

    "usageMetadata": {

        "promptTokenCount": 10,

        "candidatesTokenCount": 26,

        "totalTokenCount": 208,

        "promptTokensDetails": \[

            {

                "modality": "TEXT",

                "tokenCount": 10

            }

        \],

        "thoughtsTokenCount": 172

    },

    "modelVersion": "gemma-4-31b-it",

    "responseId": "gKflaeq2J6Pw4-EP9--piAU"

}

]

as you can see thinking is enabled. The doco says it is disabled by default.
Anyone know how to disabled it?