diff --git a/packages/llm/test/provider/openai-chat.test.ts b/packages/llm/test/provider/openai-chat.test.ts
index 9966b92e3dea..a555c1d5516c 100644
--- a/packages/llm/test/provider/openai-chat.test.ts
+++ b/packages/llm/test/provider/openai-chat.test.ts
@@ -107,6 +107,34 @@ describe("OpenAI Chat route", () => {
     }),
   )
 
+  it.effect("replays native openaiCompatible reasoning_content on assistant tool-call messages", () =>
+    Effect.gen(function* () {
+      const prepared = yield* LLMClient.prepare<OpenAIChat.OpenAIChatBody>(
+        LLM.request({
+          model,
+          messages: [
+            new Message({
+              role: "assistant",
+              content: [ToolCallPart.make({ id: "call_1", name: "bash", input: { command: "echo hello" } })],
+              native: { openaiCompatible: { reasoning_content: " " } },
+            }),
+          ],
+        }),
+      )
+
+      expect(prepared.body.messages).toEqual([
+        {
+          role: "assistant",
+          content: null,
+          tool_calls: [
+            { id: "call_1", type: "function", function: { name: "bash", arguments: '{"command":"echo hello"}' } },
+          ],
+          reasoning_content: " ",
+        },
+      ])
+    }),
+  )
+
   it.effect("adds native query params to the Chat Completions URL", () =>
     LLMClient.generate(
       LLM.updateRequest(request, {
diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index 86515068d46e..33838857f66d 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -1194,7 +1194,12 @@ function fromModelsDevModel(provider: ModelsDev.Provider, model: ModelsDev.Model
         video: model.modalities?.output?.includes("video") ?? false,
         pdf: model.modalities?.output?.includes("pdf") ?? false,
       },
-      interleaved: model.interleaved ?? false,
+      interleaved:
+        model.interleaved ??
+        ((model.provider?.npm ?? provider.npm ?? "@ai-sdk/openai-compatible") === "@ai-sdk/openai-compatible" &&
+        (model.id.includes("deepseek") || (model.id.toLowerCase().includes("kimi") && model.reasoning))
+          ? { field: "reasoning_content" }
+          : false),
     },
     release_date: model.release_date ?? "",
     variants: {},
@@ -1422,7 +1427,9 @@ export const layer = Layer.effect(
                 interleaved:
                   model.interleaved ??
                   existingModel?.capabilities.interleaved ??
-                  (!existingModel && apiNpm === "@ai-sdk/openai-compatible" && apiID.includes("deepseek")
+                  (!existingModel &&
+                  apiNpm === "@ai-sdk/openai-compatible" &&
+                  (apiID.includes("deepseek") || (apiID.toLowerCase().includes("kimi") && model.reasoning))
                     ? { field: "reasoning_content" }
                     : false),
               },
diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index 027efc0974b0..7b4cc54943e2 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -293,6 +293,7 @@ function normalizeMessages(
       if (msg.role === "assistant" && Array.isArray(msg.content)) {
         const reasoningParts = msg.content.filter((part: any) => part.type === "reasoning")
         const reasoningText = reasoningParts.map((part: any) => part.text).join("")
+        const hasToolCalls = msg.content.some((part: any) => part.type === "tool-call")
 
         // Filter out reasoning parts from content
         const filteredContent = msg.content.filter((part: any) => part.type !== "reasoning")
@@ -300,6 +301,9 @@ function normalizeMessages(
         // Include reasoning_content | reasoning_details directly on the message for all assistant messages.
         // Always set the field even when empty — some providers (e.g. DeepSeek) may return empty
         // reasoning_content which still needs to be sent back in subsequent requests.
+        // Moonshot/Kimi requires a non-empty placeholder on assistant messages that carry tool calls
+        // when thinking is enabled, otherwise the API rejects the request.
+        const fieldValue = reasoningText === "" && hasToolCalls ? " " : reasoningText
         return {
           ...msg,
           content: filteredContent,
@@ -307,7 +311,7 @@ function normalizeMessages(
             ...msg.providerOptions,
             openaiCompatible: {
               ...msg.providerOptions?.openaiCompatible,
-              [field]: reasoningText,
+              [field]: fieldValue,
             },
           },
         }
diff --git a/packages/opencode/src/session/llm/native-request.ts b/packages/opencode/src/session/llm/native-request.ts
index b7f30e24c362..730704bbd497 100644
--- a/packages/opencode/src/session/llm/native-request.ts
+++ b/packages/opencode/src/session/llm/native-request.ts
@@ -110,7 +110,7 @@ const messages = (input: readonly ModelMessage[]) => {
       Message.make({
         role: message.role,
         content: content(message.content),
-        native: isRecord(message.providerOptions) ? { providerOptions: message.providerOptions } : undefined,
+        native: isRecord(message.providerOptions) ? message.providerOptions : undefined,
       }),
     ]
   })
diff --git a/packages/opencode/test/provider/provider.test.ts b/packages/opencode/test/provider/provider.test.ts
index 6edfc97ca06e..ee54a6366a6f 100644
--- a/packages/opencode/test/provider/provider.test.ts
+++ b/packages/opencode/test/provider/provider.test.ts
@@ -276,6 +276,32 @@ it.instance(
   },
 )
 
+it.instance(
+  "custom Moonshot openai-compatible reasoning model defaults interleaved reasoning field",
+  Effect.gen(function* () {
+    const providers = yield* list
+    const provider = providers[ProviderV2.ID.make("custom-moonshot-provider")]
+    expect(provider.models["kimi-k2.5"].capabilities.interleaved).toEqual({ field: "reasoning_content" })
+    expect(provider.models["kimi-k2-non-reasoning"].capabilities.interleaved).toBe(false)
+  }),
+  {
+    config: {
+      provider: {
+        "custom-moonshot-provider": {
+          name: "Custom Moonshot Provider",
+          npm: "@ai-sdk/openai-compatible",
+          api: "https://api.custom-moonshot.com/v1",
+          models: {
+            "kimi-k2.5": { name: "Kimi K2.5", reasoning: true },
+            "kimi-k2-non-reasoning": { name: "Kimi K2 Non-Reasoning", reasoning: false },
+          },
+          options: { apiKey: "custom-key" },
+        },
+      },
+    },
+  },
+)
+
 it.instance(
   "env variable takes precedence, config merges options",
   Effect.gen(function* () {
@@ -1310,6 +1336,40 @@ test("models.dev normalization fills required response fields", () => {
   expect(model.release_date).toBe("")
 })
 
+test("models.dev Moonshot reasoning model defaults interleaved reasoning field", () => {
+  const provider = {
+    id: "moonshotai",
+    name: "Moonshot AI",
+    env: [],
+    npm: "@ai-sdk/openai-compatible",
+    api: "https://api.moonshot.ai/v1",
+    models: {
+      "kimi-k2.5": {
+        id: "kimi-k2.5",
+        name: "Kimi K2.5",
+        family: "kimi",
+        reasoning: true,
+        tool_call: true,
+        cost: { input: 0.6, output: 3 },
+        limit: { context: 262_144, output: 32_768 },
+      },
+      "kimi-v1": {
+        id: "kimi-v1",
+        name: "Kimi V1",
+        family: "kimi",
+        reasoning: false,
+        tool_call: true,
+        cost: { input: 0.6, output: 3 },
+        limit: { context: 262_144, output: 32_768 },
+      },
+    },
+  } as unknown as ModelsDev.Provider
+
+  const models = Provider.fromModelsDevProvider(provider).models
+  expect(models["kimi-k2.5"].capabilities.interleaved).toEqual({ field: "reasoning_content" })
+  expect(models["kimi-v1"].capabilities.interleaved).toBe(false)
+})
+
 it.instance("model variants are generated for reasoning models", () =>
   Effect.gen(function* () {
     yield* set("ANTHROPIC_API_KEY", "test-api-key")
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index c23a2aa9995c..702140dc00d6 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -1366,6 +1366,72 @@ describe("ProviderTransform.message - DeepSeek reasoning content", () => {
     expect(result[0].providerOptions?.openaiCompatible?.reasoning_content).toBe("Let me think about this...")
   })
 
+  test("interleaved provider injects space placeholder for tool calls without reasoning", () => {
+    const msgs = [
+      {
+        role: "assistant",
+        content: [
+          {
+            type: "tool-call",
+            toolCallId: "test",
+            toolName: "bash",
+            input: { command: "echo hello" },
+          },
+        ],
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(
+      msgs,
+      {
+        id: ModelV2.ID.make("moonshotai/kimi-k2.5"),
+        providerID: ProviderV2.ID.make("moonshotai"),
+        api: {
+          id: "kimi-k2.5",
+          url: "https://api.moonshot.ai/v1",
+          npm: "@ai-sdk/openai-compatible",
+        },
+        name: "Kimi K2.5",
+        capabilities: {
+          temperature: true,
+          reasoning: true,
+          attachment: false,
+          toolcall: true,
+          input: { text: true, audio: false, image: false, video: false, pdf: false },
+          output: { text: true, audio: false, image: false, video: false, pdf: false },
+          interleaved: {
+            field: "reasoning_content",
+          },
+        },
+        cost: {
+          input: 0.001,
+          output: 0.002,
+          cache: { read: 0.0001, write: 0.0002 },
+        },
+        limit: {
+          context: 128000,
+          output: 8192,
+        },
+        status: "active",
+        options: {},
+        headers: {},
+        release_date: "2023-04-01",
+      },
+      {},
+    )
+
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toEqual([
+      {
+        type: "tool-call",
+        toolCallId: "test",
+        toolName: "bash",
+        input: { command: "echo hello" },
+      },
+    ])
+    expect(result[0].providerOptions?.openaiCompatible?.reasoning_content).toBe(" ")
+  })
+
   test("Non-DeepSeek providers leave reasoning content unchanged", () => {
     const msgs = [
       {
diff --git a/packages/opencode/test/session/llm-native.test.ts b/packages/opencode/test/session/llm-native.test.ts
index 702bb67e390d..cfa7a8f7f46f 100644
--- a/packages/opencode/test/session/llm-native.test.ts
+++ b/packages/opencode/test/session/llm-native.test.ts
@@ -328,6 +328,26 @@ describe("session.llm-native.request", () => {
     ])
   })
 
+  test("maps message-level providerOptions to native message metadata", () => {
+    const request = LLMNative.request({
+      model: baseModel,
+      messages: [
+        {
+          role: "assistant",
+          content: [{ type: "tool-call", toolCallId: "call-1", toolName: "bash", input: { command: "ls" } }],
+          providerOptions: { openaiCompatible: { reasoning_content: " " } },
+        },
+      ],
+    })
+
+    expect(request.messages).toMatchObject([
+      {
+        role: "assistant",
+        native: { openaiCompatible: { reasoning_content: " " } },
+      },
+    ])
+  })
+
   test("selects native request routes for provider packages", () => {
     const openai = LLMNative.model({
       model: { ...baseModel, api: { ...baseModel.api, url: "", npm: "@ai-sdk/openai" } },