diff --git a/src/adapters/command-code.ts b/src/adapters/command-code.ts
index df6843ca20..6a7b95fc26 100644
--- a/src/adapters/command-code.ts
+++ b/src/adapters/command-code.ts
@@ -1,4 +1,4 @@
-import { randomUUID } from "node:crypto";
+import { createHash, randomUUID } from "node:crypto";
 import { execFile as execFileCallback } from "node:child_process";
 import { promisify } from "node:util";
 import { opendir } from "node:fs/promises";
@@ -211,6 +211,27 @@ function projectSlug(cwd: string): string {
   return cwd.replace(/[^a-zA-Z0-9]+/g, "-").replace(/^-|-$/g, "").toLowerCase().slice(0, 64) || "workspace";
 }
 
+export function commandCodeSessionId(parsed: OcxParsedRequest): string {
+  // Shared prompt-cache cohorts identify a cache population, not one conversation. Using one
+  // for session affinity would pin unrelated conversations to the same upstream worker.
+  const threadId = parsed._clientThreadId?.trim();
+  const replayId = parsed._reasoningReplayScope?.clientThreadId?.trim();
+  const cacheKey = parsed._promptCacheKeyIsSharedCohort === false
+    ? parsed.options.promptCacheKey?.trim()
+    : undefined;
+  const identity = threadId
+    ? ["thread", threadId]
+    : replayId
+      ? ["replay", replayId]
+      : cacheKey
+        ? ["cache", cacheKey]
+        : undefined;
+  if (!identity) return randomUUID();
+  const hex = createHash("sha256").update(`command-code:${identity[0]}\0${identity[1]}`).digest("hex");
+  // Replace the digest nibbles at the UUID version and variant positions; the skipped hex characters are intentional.
+  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-4${hex.slice(13, 16)}-8${hex.slice(17, 20)}-${hex.slice(20, 32)}`;
+}
+
 interface GitWorkspaceInfo {
   isGitRepo: boolean;
   currentBranch: string;
@@ -523,7 +544,7 @@ export function createCommandCodeAdapter(provider: OcxProviderConfig): ProviderA
         "x-cli-environment": "production",
         "x-taste-learning": "false",
         "x-co-flag": "false",
-        "x-session-id": randomUUID(),
+        "x-session-id": commandCodeSessionId(parsed),
       };
       if (cwd) headers["x-project-slug"] = projectSlug(cwd);
       return {
diff --git a/src/providers/registry.ts b/src/providers/registry.ts
index f78e82b965..034cb43283 100644
--- a/src/providers/registry.ts
+++ b/src/providers/registry.ts
@@ -2175,6 +2175,7 @@ export const PROVIDER_REGISTRY: readonly ProviderRegistryEntry[] = [
     liveModels: true,
     preserveCustomDestination: true,
     defaultModel: "deepseek/deepseek-v4-flash",
+    promptCacheKey: true,
     // The default is also the cold-start seed: live discovery failure must not empty the catalog
     // for a freshly configured provider with no stale cache (issue #308 pattern).
     models: ["deepseek/deepseek-v4-flash"],
diff --git a/src/server/responses/core.ts b/src/server/responses/core.ts
index 2475367d46..c194c9d372 100644
--- a/src/server/responses/core.ts
+++ b/src/server/responses/core.ts
@@ -2896,6 +2896,7 @@ async function handleResponsesInner(
   let toolBridgeMaps: ReturnType<typeof buildToolBridgeMaps>;
   try {
     parsed = parseRequest(body);
+    parsed._promptCacheKeyIsSharedCohort = options.promptCacheKeyIsSharedCohort;
     // Captured before any parser mutates it, so both grammars see the client's id.
     const { fastRow, effortRow } = parseSyntheticRowId(parsed.modelId, config);
     if (fastRow) {
@@ -3210,6 +3211,7 @@ async function handleResponsesInner(
             "_providerContinuationOwner",
             "_cursorConversationId",
             "_clientThreadId",
+            "_promptCacheKeyIsSharedCohort",
             "_cursorClientThreadId",
             "_reasoningReplayScope",
             "_cursorIsolateConversation",
diff --git a/src/types/request.ts b/src/types/request.ts
index ffee4eb8a3..1c6a5294da 100644
--- a/src/types/request.ts
+++ b/src/types/request.ts
@@ -68,6 +68,8 @@ export interface OcxParsedRequest {
   _cursorConversationId?: string;
   /** Stable upstream client thread identity, used only to derive provider-scoped continuation ids. */
   _clientThreadId?: string;
+  /** True when promptCacheKey identifies a shared cache cohort rather than one conversation. */
+  _promptCacheKeyIsSharedCohort?: boolean;
   /** Cursor-only thread owner; may be an opaque process-local Desktop session/thread identity. */
   _cursorClientThreadId?: string;
   /** Conversation/provider/account/model-bound namespace for reasoning replay state. */
diff --git a/tests/claude-integration/claude-code-thought-signature-scope.test.ts b/tests/claude-integration/claude-code-thought-signature-scope.test.ts
index 2437a8d157..eb544dce97 100644
--- a/tests/claude-integration/claude-code-thought-signature-scope.test.ts
+++ b/tests/claude-integration/claude-code-thought-signature-scope.test.ts
@@ -97,16 +97,19 @@ describe("Claude Code Anthropic inbound reasoning-replay scope", () => {
     const parsed = await drive({ promptCacheKey: "session-key-123", promptCacheKeyIsSharedCohort: false });
     expect(parsed._clientThreadId).toBeUndefined();
     expect(parsed._reasoningReplayScope?.clientThreadId).toBe("session-key-123");
+    expect(parsed._promptCacheKeyIsSharedCohort).toBe(false);
   });
 
   test("the shared Desktop prompt_cache_key cohort does not create a scope", async () => {
     const parsed = await drive({ promptCacheKey: "shared-cohort-key", promptCacheKeyIsSharedCohort: true });
     expect(parsed._reasoningReplayScope).toBeUndefined();
+    expect(parsed._promptCacheKeyIsSharedCohort).toBe(true);
   });
 
   test("an Anthropic replay without prompt_cache_key does not create a scope", async () => {
     const parsed = await drive({});
     expect(parsed._reasoningReplayScope).toBeUndefined();
+    expect(parsed._promptCacheKeyIsSharedCohort).toBeUndefined();
   });
 
   test("an overlong prompt_cache_key is hashed, not stored raw", async () => {
diff --git a/tests/providers/command-code-provider.test.ts b/tests/providers/command-code-provider.test.ts
index e4bb3c4d90..06b096586a 100644
--- a/tests/providers/command-code-provider.test.ts
+++ b/tests/providers/command-code-provider.test.ts
@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, test } from "bun:test";
-import { createCommandCodeAdapter } from "../../src/adapters/command-code";
+import { commandCodeSessionId, createCommandCodeAdapter } from "../../src/adapters/command-code";
 import { loginCommandCode, parseCommandCodeCallback, shouldImportLocalCommandCodeAuth } from "../../src/oauth/command-code";
 import { buildModelsRequest, OAUTH_PROVIDERS } from "../../src/oauth";
 import {
@@ -658,4 +658,68 @@ describe("Command Code provider", () => {
     const built = await builtRequest({ ...parsed(), stream: false });
     expect(JSON.parse(built.body).params.stream).toBe(true);
   });
+
+  test("derives an opaque stable session id from trusted conversation identity", async () => {
+    const uuid = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-8[0-9a-f]{3}-[0-9a-f]{12}$/i;
+    const identities = {
+      thread: "thread-secret-value",
+      replay: "replay-secret-value",
+      cache: "cache-secret-value",
+    };
+    const thread = {
+      ...parsed(),
+      _clientThreadId: `  ${identities.thread}  `,
+      _reasoningReplayScope: { clientThreadId: identities.replay },
+      options: { ...parsed().options, promptCacheKey: identities.cache },
+    };
+    const sameThread = {
+      ...thread,
+      _reasoningReplayScope: { clientThreadId: "different-replay" },
+      options: { ...thread.options, promptCacheKey: "different-cache" },
+    };
+    const replay = {
+      ...parsed(),
+      _reasoningReplayScope: { clientThreadId: identities.replay },
+      options: { ...parsed().options, promptCacheKey: identities.cache },
+    };
+    const sameReplay = { ...replay, options: { ...replay.options, promptCacheKey: "different-cache" } };
+    const cache = {
+      ...parsed(),
+      options: { ...parsed().options, promptCacheKey: ` ${identities.cache} ` },
+      _promptCacheKeyIsSharedCohort: false,
+    };
+    const sameCache = {
+      ...cache,
+      options: { ...cache.options, promptCacheKey: identities.cache },
+    };
+
+    const threadId = commandCodeSessionId(thread);
+    expect(threadId).toBe(commandCodeSessionId(sameThread));
+    expect(threadId).not.toBe(commandCodeSessionId({ ...thread, _clientThreadId: "different-thread" }));
+    expect(commandCodeSessionId(replay)).toBe(commandCodeSessionId(sameReplay));
+    expect(commandCodeSessionId(cache)).toBe(commandCodeSessionId(sameCache));
+    expect(commandCodeSessionId(replay)).not.toBe(commandCodeSessionId(cache));
+    expect(threadId).toMatch(uuid);
+    expect(commandCodeSessionId(replay)).toMatch(uuid);
+    expect(commandCodeSessionId(cache)).toMatch(uuid);
+    for (const raw of Object.values(identities)) expect(threadId).not.toContain(raw);
+
+    const built = await builtRequest(thread);
+    expect(built.headers["x-session-id"]).toBe(threadId);
+  });
+
+  test("does not derive affinity from a shared cohort or prompt text", () => {
+    const shared = {
+      ...parsed(),
+      options: { ...parsed().options, promptCacheKey: "shared-cache-key" },
+      _promptCacheKeyIsSharedCohort: true,
+    };
+    expect(commandCodeSessionId(shared)).not.toBe(commandCodeSessionId(shared));
+    const unclassifiedCache = {
+      ...parsed(),
+      options: { ...parsed().options, promptCacheKey: "possibly-shared-cache-key" },
+    };
+    expect(commandCodeSessionId(unclassifiedCache)).not.toBe(commandCodeSessionId(unclassifiedCache));
+    expect(commandCodeSessionId(parsed())).not.toBe(commandCodeSessionId(parsed()));
+  });
 });
diff --git a/tests/providers/commandcode-provider.test.ts b/tests/providers/commandcode-provider.test.ts
index e76355dc4f..f70df51093 100644
--- a/tests/providers/commandcode-provider.test.ts
+++ b/tests/providers/commandcode-provider.test.ts
@@ -67,6 +67,7 @@ describe("Command Code provider", () => {
       liveModels: true,
       preserveCustomDestination: true,
       defaultModel: "deepseek/deepseek-v4-flash",
+      promptCacheKey: true,
       apiKeyValidation: "unknown",
       reasoningEfforts: [],
       modelReasoningEfforts: {
@@ -176,6 +177,20 @@ describe("Command Code provider", () => {
     expect(body).not.toHaveProperty("parallel_tool_calls");
   });
 
+  test("forwards the enabled prompt cache key to chat completions", () => {
+    const route = routeModel(
+      commandcodeConfig(),
+      "commandcode/deepseek/deepseek-v4-flash",
+    );
+    const request = createOpenAIChatAdapter(route.provider).buildRequest({
+      modelId: route.modelId,
+      context: { messages: [{ role: "user", content: "ping", timestamp: 0 }] },
+      stream: true,
+      options: { promptCacheKey: "command-code-session-cache" },
+    });
+    expect(JSON.parse(String(request.body)).prompt_cache_key).toBe("command-code-session-cache");
+  });
+
   test("discovers the live catalog with context windows and preserves slash ids", async () => {
     globalThis.fetch = (async (input, init) => {
       expect(String(input)).toBe("https://api.commandcode.ai/provider/v1/models");