diff --git a/src/provider/openai-compatible-adapter.test.ts b/src/provider/openai-compatible-adapter.test.ts
index 518ff29b5..41ec48e69 100644
--- a/src/provider/openai-compatible-adapter.test.ts
+++ b/src/provider/openai-compatible-adapter.test.ts
@@ -164,3 +164,84 @@ describe("openai-compatible adapter reasoning_content handling", () => {
     expect(assistant?.["reasoning_content"]).toBe("ponder");
   });
 });
+
+describe("openai-compatible adapter DeepSeek V4 Flash wire params", () => {
+  const V4 = "deepseek-ai/DeepSeek-V4-Flash-0731";
+  const history: ConversationTurn[] = [
+    { role: "user", content: [{ type: "text", text: "hi" }] },
+    {
+      role: "assistant",
+      content: [
+        { type: "thinking", thinking: "ponder" },
+        { type: "text", text: "hello" },
+      ],
+    },
+    { role: "user", content: [{ type: "text", text: "again" }] },
+  ] as unknown as ConversationTurn[];
+
+  function v4Body(
+    providerOptions?: Record<string, unknown>,
+    model = V4,
+  ): Record<string, unknown> {
+    const adapter = createOpenAICompatibleAdapter(source);
+    const built = adapter.buildRequest(history, model, {
+      maxTokens: 100,
+      ...(providerOptions !== undefined ? { providerOptions } : {}),
+    } as InferenceOptions);
+    return JSON.parse(built.body) as Record<string, unknown>;
+  }
+
+  test("turns thinking on and applies agentic sampling at high effort", () => {
+    const body = v4Body({ reasoning_effort: "high" });
+    expect(body["chat_template_kwargs"]).toEqual({ thinking: true });
+    expect(body["reasoning_effort"]).toBe("high");
+    expect(body["temperature"]).toBe(1);
+    expect(body["top_p"]).toBe(0.95);
+    expect(body["stream_options"]).toEqual({ include_usage: true });
+  });
+
+  test("folds Corbits' ladder onto low/high/max", () => {
+    expect(v4Body({ reasoning_effort: "minimal" })["reasoning_effort"]).toBe(
+      "low",
+    );
+    expect(v4Body({ reasoning_effort: "medium" })["reasoning_effort"]).toBe(
+      "high",
+    );
+    expect(v4Body({ reasoning_effort: "max" })["reasoning_effort"]).toBe("max");
+  });
+
+  test("effort none sends chat mode explicitly and no effort", () => {
+    const body = v4Body({ reasoning_effort: "none" });
+    expect(body["chat_template_kwargs"]).toEqual({ thinking: false });
+    expect("reasoning_effort" in body).toBe(false);
+    expect("top_p" in body).toBe(false);
+  });
+
+  test("an explicitly configured temperature/top_p wins", () => {
+    const body = v4Body({
+      reasoning_effort: "high",
+      temperature: 0.6,
+      top_p: 0.9,
+    });
+    expect(body["temperature"]).toBe(0.6);
+    expect(body["top_p"]).toBe(0.9);
+  });
+
+  test("replays reasoning_content on prior assistant turns", () => {
+    const msgs = v4Body({ reasoning_effort: "high" })["messages"] as Record<
+      string,
+      unknown
+    >[];
+    const assistant = msgs.find((m) => m["role"] === "assistant");
+    expect(assistant?.["reasoning_content"]).toBe("ponder");
+  });
+
+  test("other DeepSeek models keep the old strip and get no extra params", () => {
+    const body = v4Body({ reasoning_effort: "high" }, "deepseek-v3.2");
+    expect("chat_template_kwargs" in body).toBe(false);
+    expect("top_p" in body).toBe(false);
+    const msgs = body["messages"] as Record<string, unknown>[];
+    const assistant = msgs.find((m) => m["role"] === "assistant");
+    expect("reasoning_content" in defined(assistant)).toBe(false);
+  });
+});
diff --git a/src/provider/openai-compatible-adapter.ts b/src/provider/openai-compatible-adapter.ts
index d869af801..4ac3518b0 100644
--- a/src/provider/openai-compatible-adapter.ts
+++ b/src/provider/openai-compatible-adapter.ts
@@ -45,11 +45,13 @@ export function createOpenAICompatibleAdapter(
     const providerOptions = options.providerOptions;
     const hasProviderOptions =
       providerOptions !== undefined && Object.keys(providerOptions).length > 0;
-    // DeepSeek returns HTTP 400 if `reasoning_content` appears in input messages,
-    // whereas the base adapter emits it for any model with thinking enabled.
-    const stripReasoning = model.toLowerCase().includes("deepseek");
-    needsDeepSeekPatch = stripReasoning;
-    if (!hasProviderOptions && !stripReasoning) return ensureAccept(built);
+    // Earlier DeepSeek models 400 on `reasoning_content` in input messages;
+    // V4 Flash keeps it because its encoder preserves each turn's thinking.
+    const v4Flash = isDeepSeekV4Flash(model);
+    const stripReasoning = model.toLowerCase().includes("deepseek") && !v4Flash;
+    needsDeepSeekPatch = model.toLowerCase().includes("deepseek");
+    if (!hasProviderOptions && !stripReasoning && !v4Flash)
+      return ensureAccept(built);
 
     const body = JSON.parse(built.body) as Record<string, unknown>;
     if (hasProviderOptions) Object.assign(body, providerOptions);
@@ -59,6 +61,7 @@ export function createOpenAICompatibleAdapter(
           delete (msg as Record<string, unknown>)["reasoning_content"];
       }
     }
+    if (v4Flash) applyDeepSeekV4FlashParams(body);
     const merged: BuiltRequest = { ...built, body: JSON.stringify(body) };
     return ensureAccept(merged);
   };
@@ -73,3 +76,46 @@ export function createOpenAICompatibleAdapter(
 
   return { ...base, buildRequest, parseResponse };
 }
+
+/** True for DeepSeek V4 Flash on any OpenAI-compatible host. */
+export function isDeepSeekV4Flash(model: string): boolean {
+  return /(^|\/)deepseek-v4-flash/i.test(model.trim());
+}
+
+// DeepSeek V4 understands exactly three reasoning_effort levels (low, high,
+// max); its reference encoder asserts on anything else. Corbits' generic
+// ladder (minimal/low/medium/high/xhigh/max) is folded onto those three.
+const DSV4_EFFORT: Record<string, "low" | "high" | "max"> = {
+  minimal: "low",
+  low: "low",
+  medium: "high",
+  high: "high",
+  xhigh: "max",
+  max: "max",
+};
+
+/** Apply the DeepSeek V4 Flash wire shape to an already-built chat body. */
+export function applyDeepSeekV4FlashParams(
+  body: Record<string, unknown>,
+): void {
+  const raw = body["reasoning_effort"];
+  const effort = typeof raw === "string" ? raw.toLowerCase() : undefined;
+  const thinking =
+    effort !== undefined && effort !== "none" && effort !== "off";
+  const existingKwargs =
+    body["chat_template_kwargs"] !== null &&
+    typeof body["chat_template_kwargs"] === "object"
+      ? (body["chat_template_kwargs"] as Record<string, unknown>)
+      : {};
+  body["chat_template_kwargs"] = { ...existingKwargs, thinking };
+  if (thinking) {
+    body["reasoning_effort"] = DSV4_EFFORT[effort] ?? "high";
+    if (body["temperature"] === undefined) body["temperature"] = 1.0;
+    if (body["top_p"] === undefined) body["top_p"] = 0.95;
+  } else {
+    delete body["reasoning_effort"];
+  }
+  if (body["stream"] === true && body["stream_options"] === undefined) {
+    body["stream_options"] = { include_usage: true };
+  }
+}
diff --git a/src/subagent/provider-family.ts b/src/subagent/provider-family.ts
index 8a42497e4..48adefad7 100644
--- a/src/subagent/provider-family.ts
+++ b/src/subagent/provider-family.ts
@@ -83,8 +83,23 @@ export function isGptProvider(input: {
   return false;
 }
 
+/**
+ * True when the model id is DeepSeek V4 Flash (any provider). Scoped to the
+ * Flash cell only: the residual it unlocks was tuned against that model.
+ */
+export function isDeepSeekV4FlashProvider(input: {
+  providerName: string;
+  model?: string;
+}): boolean {
+  return (
+    input.model !== undefined &&
+    /(^|\/)deepseek-v4-flash/i.test(input.model.trim())
+  );
+}
+
 /** Model families the shared directors branch on via ModelFamilyPolicy. */
 export type ModelFamily =
+  | "deepseek-v4-flash"
   | "grok"
   | "kimi"
   | "muse"
@@ -103,6 +118,7 @@ export function detectModelFamily(input: {
   providerName: string;
   model?: string;
 }): ModelFamily {
+  if (isDeepSeekV4FlashProvider(input)) return "deepseek-v4-flash";
   if (isXaiGrokLeafProvider(input)) return "grok";
   if (isKimiLeafProvider(input)) return "kimi";
   if (isMuseSparkLeafProvider(input)) return "muse";