diff --git a/packages/core/src/session/runner/llm.ts b/packages/core/src/session/runner/llm.ts
index 874086a06bd..b509f3cb745 100644
--- a/packages/core/src/session/runner/llm.ts
+++ b/packages/core/src/session/runner/llm.ts
@@ -206,6 +206,8 @@ const layer = Layer.effect(
         model,
         http: {
           headers: {
+            "x-opencode-session-id": session.id,
+            ...(session.parentID ? { "x-opencode-parent-session-id": session.parentID } : {}),
             "x-session-affinity": session.id,
             "X-Session-Id": session.id,
             ...(session.parentID ? { "x-parent-session-id": session.parentID } : {}),
diff --git a/packages/core/test/session-runner.test.ts b/packages/core/test/session-runner.test.ts
index cc58b43b295..d2a34bf65ce 100644
--- a/packages/core/test/session-runner.test.ts
+++ b/packages/core/test/session-runner.test.ts
@@ -1103,10 +1103,12 @@ describe("SessionRunnerLLM", () => {
       expect(requests).toHaveLength(2)
       expect(requests.map((request) => request.http?.headers)).toEqual([
         {
+          "x-opencode-session-id": sessionID,
           "x-session-affinity": sessionID,
           "X-Session-Id": sessionID,
         },
         {
+          "x-opencode-session-id": sessionID,
           "x-session-affinity": sessionID,
           "X-Session-Id": sessionID,
         },
@@ -2528,6 +2530,7 @@ describe("SessionRunnerLLM", () => {
       yield* session.resume(sessionID)
 
       expect(requests[0]?.http?.headers).toEqual({
+        "x-opencode-session-id": sessionID,
         "x-session-affinity": sessionID,
         "X-Session-Id": sessionID,
       })
@@ -2551,7 +2554,13 @@ describe("SessionRunnerLLM", () => {
       requests.length = 0
       yield* session.resume(sessionID)
 
-      expect(requests[0]?.http?.headers?.["x-parent-session-id"]).toBe(parentID)
+      expect(requests[0]?.http?.headers).toEqual({
+        "x-opencode-session-id": sessionID,
+        "x-opencode-parent-session-id": parentID,
+        "x-session-affinity": sessionID,
+        "X-Session-Id": sessionID,
+        "x-parent-session-id": parentID,
+      })
     }),
   )
 
diff --git a/packages/opencode/src/session/llm/request.ts b/packages/opencode/src/session/llm/request.ts
index e000d6ca49b..a945b66f7e8 100644
--- a/packages/opencode/src/session/llm/request.ts
+++ b/packages/opencode/src/session/llm/request.ts
@@ -185,6 +185,8 @@ export const prepare = Effect.fn("LLMRequestPrep.prepare")(function* (input: Pre
     params,
     messageTransformOptions: options,
     headers: {
+      "x-opencode-session-id": input.sessionID,
+      ...(input.parentSessionID ? { "x-opencode-parent-session-id": input.parentSessionID } : {}),
       ...(input.model.providerID.startsWith("opencode")
         ? {
             ...(opencodeProjectID ? { "x-opencode-project": opencodeProjectID } : {}),
diff --git a/packages/opencode/test/session/llm.test.ts b/packages/opencode/test/session/llm.test.ts
index fcb536f46d9..ed0ad2022e2 100644
--- a/packages/opencode/test/session/llm.test.ts
+++ b/packages/opencode/test/session/llm.test.ts
@@ -756,72 +756,89 @@ describe("session.llm.stream", () => {
   const vivgridFixture = { providerID: "vivgrid", modelID: "gemini-3.1-pro-preview" }
   const opencodeFixture = { providerID: "opencode-test", modelID: vivgridFixture.modelID }
 
-  it.instance(
-    "sends the parent session header for opencode providers",
-    () =>
-      Effect.gen(function* () {
-        const fixture = loadFixture(vivgridFixture.providerID, vivgridFixture.modelID)
-        const request = waitRequest(
-          "/chat/completions",
-          new Response(createChatStream("Hello"), {
-            status: 200,
-            headers: { "Content-Type": "text/event-stream" },
-          }),
-        )
-        const resolved = yield* Provider.use.getModel(
-          ProviderV2.ID.make(opencodeFixture.providerID),
-          ModelV2.ID.make(opencodeFixture.modelID),
-        )
-        const sessionID = SessionID.make("session-child")
-        const parentSessionID = SessionID.make("session-parent")
-        const agent = {
-          name: "test",
-          mode: "primary",
-          options: {},
-          permission: [{ permission: "*", pattern: "*", action: "allow" }],
-        } satisfies Agent.Info
-        const user = {
-          id: MessageID.make("msg_user-parent-header"),
-          sessionID,
-          role: "user",
-          time: { created: Date.now() },
-          agent: agent.name,
-          model: {
-            providerID: ProviderV2.ID.make(opencodeFixture.providerID),
-            modelID: resolved.id,
-          },
-        } satisfies SessionV1.User
-
-        yield* drain({
-          user,
-          sessionID,
-          parentSessionID,
-          model: resolved,
-          agent,
-          system: ["You are a helpful assistant."],
-          messages: [{ role: "user", content: "Hello" }],
-          tools: {},
-        })
-
-        expect((yield* Effect.promise(() => request)).headers.get("x-parent-session-id")).toBe(parentSessionID)
-      }),
-    {
-      config: () => {
-        const fixture = loadFixture(vivgridFixture.providerID, vivgridFixture.modelID)
-        return {
-          enabled_providers: [opencodeFixture.providerID],
-          provider: {
-            [opencodeFixture.providerID]: {
-              name: "OpenCode Test",
-              npm: "@ai-sdk/openai-compatible",
-              models: { [fixture.model.id]: configModel(fixture.model) as ConfigModel },
-              options: { apiKey: "test-key", baseURL: `${state.server!.url.origin}/v1` },
+  const headerCases = [
+    { providerID: opencodeFixture.providerID, child: false },
+    { providerID: opencodeFixture.providerID, child: true },
+    { providerID: "custom-test", child: false },
+    { providerID: "custom-test", child: true },
+  ]
+  headerCases.forEach((input) => {
+    it.instance(
+      `sends session identity headers for ${input.child ? "child" : "root"} sessions on ${input.providerID}`,
+      () =>
+        Effect.gen(function* () {
+          const fixture = loadFixture(vivgridFixture.providerID, vivgridFixture.modelID)
+          const request = waitRequest(
+            "/chat/completions",
+            new Response(createChatStream("Hello"), {
+              status: 200,
+              headers: { "Content-Type": "text/event-stream" },
+            }),
+          )
+          const resolved = yield* Provider.use.getModel(
+            ProviderV2.ID.make(input.providerID),
+            ModelV2.ID.make(opencodeFixture.modelID),
+          )
+          const sessionID = SessionID.make("session-child")
+          const parentSessionID = input.child ? SessionID.make("session-parent") : undefined
+          const agent = {
+            name: "test",
+            mode: "primary",
+            options: {},
+            permission: [{ permission: "*", pattern: "*", action: "allow" }],
+          } satisfies Agent.Info
+          const user = {
+            id: MessageID.make("msg_user-parent-header"),
+            sessionID,
+            role: "user",
+            time: { created: Date.now() },
+            agent: agent.name,
+            model: {
+              providerID: ProviderV2.ID.make(input.providerID),
+              modelID: resolved.id,
             },
-          },
-        }
+          } satisfies SessionV1.User
+
+          yield* drain({
+            user,
+            sessionID,
+            parentSessionID,
+            model: resolved,
+            agent,
+            system: ["You are a helpful assistant."],
+            messages: [{ role: "user", content: "Hello" }],
+            tools: {},
+          })
+
+          const headers = (yield* Effect.promise(() => request)).headers
+          expect(headers.get("x-opencode-session-id")).toBe(sessionID)
+          expect(headers.get("x-opencode-parent-session-id")).toBe(parentSessionID ?? null)
+          expect(headers.get("x-parent-session-id")).toBe(parentSessionID ?? null)
+          if (input.providerID.startsWith("opencode")) {
+            expect(headers.get("x-opencode-session")).toBe(sessionID)
+            return
+          }
+          expect(headers.get("x-session-affinity")).toBe(sessionID)
+          expect(headers.get("X-Session-Id")).toBe(sessionID)
+        }),
+      {
+        config: () => {
+          const fixture = loadFixture(vivgridFixture.providerID, vivgridFixture.modelID)
+          return {
+            enabled_providers: [input.providerID],
+            provider: {
+              [input.providerID]: {
+                name: "OpenCode Test",
+                npm: "@ai-sdk/openai-compatible",
+                models: { [fixture.model.id]: configModel(fixture.model) as ConfigModel },
+                options: { apiKey: "test-key", baseURL: `${state.server!.url.origin}/v1` },
+              },
+            },
+          }
+        },
       },
-    },
-  )
+    )
+  })
 
   it.instance(
     "sends temperature, tokens, and reasoning options for openai-compatible models",