diff --git a/packages/opencode/src/provider/models.ts b/packages/opencode/src/provider/models.ts
index 3d28787c88f..e145d867e00 100644
--- a/packages/opencode/src/provider/models.ts
+++ b/packages/opencode/src/provider/models.ts
@@ -15,6 +15,7 @@ export namespace ModelsDev {
     release_date: z.string(),
     attachment: z.boolean(),
     reasoning: z.boolean(),
+    interleaved_thinking: z.boolean().optional(),
     temperature: z.boolean(),
     tool_call: z.boolean(),
     cost: z
diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index 14adccf1c49..1ce0c39d723 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -325,6 +325,7 @@ export namespace Provider {
       capabilities: z.object({
         temperature: z.boolean(),
         reasoning: z.boolean(),
+        interleavedthinking: z.boolean().optional(),
         attachment: z.boolean(),
         toolcall: z.boolean(),
         input: z.object({
@@ -426,6 +427,7 @@ export namespace Provider {
       capabilities: {
         temperature: model.temperature,
         reasoning: model.reasoning,
+        interleavedthinking: model.interleaved_thinking ?? false,
         attachment: model.attachment,
         toolcall: model.tool_call,
         input: {
@@ -543,6 +545,7 @@ export namespace Provider {
           capabilities: {
             temperature: model.temperature ?? existingModel?.capabilities.temperature ?? false,
             reasoning: model.reasoning ?? existingModel?.capabilities.reasoning ?? false,
+            interleavedthinking: model.interleaved_thinking ?? existingModel?.capabilities.interleavedthinking ?? false,
             attachment: model.attachment ?? existingModel?.capabilities.attachment ?? false,
             toolcall: model.tool_call ?? existingModel?.capabilities.toolcall ?? true,
             input: {
diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 09dfd69a317..7bed7923026 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -103,6 +103,28 @@ export namespace ProviderTransform {
       })
     }
 
+    // For models with interleaved thinking enabled, convert reasoning parts to text parts
+    // so the reasoning content is included in the API request. This is necessary because
+    // the AI SDK's OpenAI provider ignores reasoning parts when converting to chat messages.
+    if (model.capabilities.interleavedthinking) {
+      return msgs.map((msg) => {
+        if (msg.role === "assistant" && Array.isArray(msg.content)) {
+          // Convert reasoning parts to text parts
+          msg.content = msg.content.map((part: any) => {
+            if (part.type === "reasoning" && part.text) {
+              return {
+                type: "text",
+                text: part.text,
+                providerOptions: part.providerOptions,
+              }
+            }
+            return part
+          })
+        }
+        return msg
+      })
+    }
+
     return msgs
   }
 
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 648f108bd66..c4f2d38d174 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -126,6 +126,7 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
       capabilities: {
         temperature: true,
         reasoning: true,
+        interleavedthinking: false,
         attachment: false,
         toolcall: true,
         input: { text: true, audio: false, image: false, video: false, pdf: false },
@@ -180,6 +181,7 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
       capabilities: {
         temperature: true,
         reasoning: true,
+        interleavedthinking: false,
         attachment: false,
         toolcall: true,
         input: { text: true, audio: false, image: false, video: false, pdf: false },
@@ -232,6 +234,7 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
       capabilities: {
         temperature: true,
         reasoning: true,
+        interleavedthinking: false,
         attachment: false,
         toolcall: true,
         input: { text: true, audio: false, image: false, video: false, pdf: false },
@@ -277,6 +280,7 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
       capabilities: {
         temperature: true,
         reasoning: false,
+        interleavedthinking: false,
         attachment: true,
         toolcall: true,
         input: { text: true, audio: false, image: true, video: false, pdf: false },
@@ -303,3 +307,114 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
     expect(result[0].providerOptions?.openaiCompatible?.reasoning_content).toBeUndefined()
   })
 })
+
+describe("ProviderTransform.message - Interleaved thinking", () => {
+  test("Converts reasoning parts to text parts", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          { type: "reasoning", text: "Let me analyze this step by step..." },
+          {
+            type: "tool-call",
+            toolCallId: "test",
+            toolName: "bash",
+            input: { command: "git diff" },
+          },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, {
+      id: "openai/gpt-4",
+      providerID: "openai",
+      api: {
+        id: "gpt-4",
+        url: "https://api.openai.com",
+        npm: "@ai-sdk/openai",
+      },
+      name: "GPT-4",
+      capabilities: {
+        temperature: true,
+        reasoning: false,
+        attachment: true,
+        toolcall: true,
+        interleavedthinking: true,
+        input: { text: true, audio: false, image: false, video: false, pdf: false },
+        output: { text: true, audio: false, image: false, video: false, pdf: false },
+      },
+      cost: {
+        input: 0.03,
+        output: 0.06,
+        cache: { read: 0.001, write: 0.002 },
+      },
+      limit: {
+        context: 128000,
+        output: 4096,
+      },
+      status: "active",
+      options: {},
+      headers: {},
+    })
+
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toEqual([
+      { type: "text", text: "Let me analyze this step by step...", providerOptions: undefined },
+      {
+        type: "tool-call",
+        toolCallId: "test",
+        toolName: "bash",
+        input: { command: "git diff" },
+      },
+    ])
+  })
+
+  test("Preserves reasoning parts when interleavedthinking is false", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          { type: "reasoning", text: "Reasoning that should stay as-is" },
+          { type: "text", text: "Answer" },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, {
+      id: "openai/gpt-4",
+      providerID: "openai",
+      api: {
+        id: "gpt-4",
+        url: "https://api.openai.com",
+        npm: "@ai-sdk/openai",
+      },
+      name: "GPT-4",
+      capabilities: {
+        temperature: true,
+        reasoning: false,
+        interleavedthinking: false,
+        attachment: true,
+        toolcall: true,
+        input: { text: true, audio: false, image: false, video: false, pdf: false },
+        output: { text: true, audio: false, image: false, video: false, pdf: false },
+      },
+      cost: {
+        input: 0.03,
+        output: 0.06,
+        cache: { read: 0.001, write: 0.002 },
+      },
+      limit: {
+        context: 128000,
+        output: 4096,
+      },
+      status: "active",
+      options: {},
+      headers: {},
+    })
+
+    expect(result[0].content).toEqual([
+      { type: "reasoning", text: "Reasoning that should stay as-is" },
+      { type: "text", text: "Answer" },
+    ])
+  })
+})