diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index c25476a8850..cc1b0f719aa 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -1160,7 +1160,12 @@ 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("step")
+          ? { field: "reasoning_content" as const }
+          : false),
     },
     release_date: model.release_date ?? "",
     variants: {},
@@ -1397,10 +1402,11 @@ export const layer = Layer.effect(
                 },
                 interleaved:
                   model.interleaved ??
-                  existingModel?.capabilities.interleaved ??
-                  (!existingModel && apiNpm === "@ai-sdk/openai-compatible" && apiID.includes("deepseek")
-                    ? { field: "reasoning_content" }
-                    : false),
+                  (existingModel?.capabilities.interleaved
+                    ? existingModel.capabilities.interleaved
+                    : apiNpm === "@ai-sdk/openai-compatible" && (apiID.includes("deepseek") || apiID.includes("step"))
+                      ? { field: "reasoning_content" as const }
+                      : false),
               },
               cost: {
                 input: model?.cost?.input ?? existingModel?.cost?.input ?? 0,
diff --git a/packages/opencode/test/kilocode/provider/stepfun-interleaved.test.ts b/packages/opencode/test/kilocode/provider/stepfun-interleaved.test.ts
new file mode 100644
index 00000000000..e9069bd8bf9
--- /dev/null
+++ b/packages/opencode/test/kilocode/provider/stepfun-interleaved.test.ts
@@ -0,0 +1,149 @@
+import { expect, test } from "bun:test"
+import { Effect } from "effect"
+import { ModelsDev } from "@opencode-ai/core/models-dev"
+import { Provider } from "../../../src/provider/provider"
+import { ProviderID } from "../../../src/provider/schema"
+import { testEffect } from "../../lib/effect"
+
+const it = testEffect(Provider.defaultLayer)
+
+const base = (id: string): ModelsDev.Model => ({
+  id,
+  name: id,
+  release_date: "2026-01-01",
+  attachment: false,
+  reasoning: true,
+  temperature: true,
+  tool_call: true,
+  limit: {
+    context: 128000,
+    output: 8192,
+  },
+})
+
+test("StepFun catalog models default to interleaved reasoning_content", () => {
+  const provider = Provider.fromModelsDevProvider({
+    id: "stepfun",
+    name: "StepFun",
+    env: ["STEPFUN_API_KEY"],
+    npm: "@ai-sdk/openai-compatible",
+    api: "https://api.stepfun.com/v1",
+    models: {
+      "step-3.5-flash": base("step-3.5-flash"),
+    },
+  })
+
+  expect(provider.models["step-3.5-flash"].capabilities.interleaved).toEqual({
+    field: "reasoning_content",
+  })
+})
+
+test("StepFun provider does not default when model ID does not include step", () => {
+  const provider = Provider.fromModelsDevProvider({
+    id: "stepfun",
+    name: "StepFun",
+    env: ["STEPFUN_API_KEY"],
+    npm: "@ai-sdk/openai-compatible",
+    api: "https://api.stepfun.com/v1",
+    models: {
+      custom: {
+        ...base("custom"),
+        name: "Custom Model",
+      },
+    },
+  })
+
+  expect(provider.models["custom"].capabilities.interleaved).toBe(false)
+})
+
+test("catalog DeepSeek models do not default to interleaved reasoning_content", () => {
+  const provider = Provider.fromModelsDevProvider({
+    id: "custom-provider",
+    name: "Custom Provider",
+    env: ["CUSTOM_API_KEY"],
+    npm: "@ai-sdk/openai-compatible",
+    api: "https://api.custom.com/v1",
+    models: {
+      "deepseek-r1": base("deepseek-r1"),
+    },
+  })
+
+  expect(provider.models["deepseek-r1"].capabilities.interleaved).toBe(false)
+})
+
+test("catalog model IDs containing step default to interleaved reasoning_content", () => {
+  const provider = Provider.fromModelsDevProvider({
+    id: "custom-provider",
+    name: "Custom Provider",
+    env: ["CUSTOM_API_KEY"],
+    npm: "@ai-sdk/openai-compatible",
+    api: "https://api.custom.com/v1",
+    models: {
+      space: base("step 3.5 flash"),
+      hyphen: base("step-3.5-flash"),
+      dot: base("step.3.5.flash"),
+      underscore: base("step_3_5_flash"),
+    },
+  })
+
+  for (const model of Object.values(provider.models)) {
+    expect(model.capabilities.interleaved).toEqual({
+      field: "reasoning_content",
+    })
+  }
+})
+
+test("catalog model IDs containing step do not default for non-openai-compatible providers", () => {
+  const provider = Provider.fromModelsDevProvider({
+    id: "custom-provider",
+    name: "Custom Provider",
+    env: ["CUSTOM_API_KEY"],
+    npm: "@kilocode/kilo-gateway",
+    api: "https://api.custom.com/v1",
+    models: {
+      custom: base("step-3.5-flash"),
+    },
+  })
+
+  expect(provider.models["custom"].capabilities.interleaved).toBe(false)
+})
+
+it.instance(
+  "configured StepFun and step model IDs default to interleaved reasoning_content",
+  Effect.gen(function* () {
+    const providers = yield* Provider.use.list()
+    const stepfun = providers[ProviderID.make("stepfun")].models["step-custom"]
+    const custom = providers[ProviderID.make("custom-provider")].models["custom-step"]
+
+    expect(stepfun.capabilities.interleaved).toEqual({
+      field: "reasoning_content",
+    })
+    expect(custom.capabilities.interleaved).toEqual({
+      field: "reasoning_content",
+    })
+  }),
+  {
+    config: {
+      provider: {
+        stepfun: {
+          name: "StepFun",
+          npm: "@ai-sdk/openai-compatible",
+          api: "https://api.stepfun.com/v1",
+          models: {
+            "step-custom": { name: "Step Custom" },
+          },
+          options: { apiKey: "test-key" },
+        },
+        "custom-provider": {
+          name: "Custom Provider",
+          npm: "@ai-sdk/openai-compatible",
+          api: "https://api.custom.com/v1",
+          models: {
+            "custom-step": { id: "step-3.5-flash", name: "Custom Alias" },
+          },
+          options: { apiKey: "test-key" },
+        },
+      },
+    },
+  },
+)