diff --git a/packages/core/src/config/lsp.ts b/packages/core/src/config/lsp.ts
index 651597befdde..2f7a28ccb214 100644
--- a/packages/core/src/config/lsp.ts
+++ b/packages/core/src/config/lsp.ts
@@ -12,6 +12,14 @@ export class Server extends Schema.Class<Server>("ConfigV2.LSP.Server")({
   disabled: Schema.Boolean.pipe(Schema.optional),
   env: Schema.Record(Schema.String, Schema.String).pipe(Schema.optional),
   initialization: Schema.Record(Schema.String, Schema.Unknown).pipe(Schema.optional),
+  // How long to wait for diagnostics, in milliseconds. Defaults suit servers
+  // that respond quickly; a large C++ translation unit can take far longer to
+  // parse than the default wait, in which case the client gives up and reports
+  // no diagnostics at all — indistinguishable from a clean file.
+  timeout: Schema.Struct({
+    document: Schema.Number.pipe(Schema.optional),
+    full: Schema.Number.pipe(Schema.optional),
+  }).pipe(Schema.optional),
 }) {}
 
 export const Entry = Schema.Union([Disabled, Server])
diff --git a/packages/core/src/v1/config/lsp.ts b/packages/core/src/v1/config/lsp.ts
index 89a58b5b2c9b..bdcc9a7298c2 100644
--- a/packages/core/src/v1/config/lsp.ts
+++ b/packages/core/src/v1/config/lsp.ts
@@ -14,6 +14,15 @@ export const Entry = Schema.Union([
     disabled: Schema.optional(Schema.Boolean),
     env: Schema.optional(Schema.Record(Schema.String, Schema.String)),
     initialization: Schema.optional(Schema.Record(Schema.String, Schema.Unknown)),
+    // Must mirror the v2 schema. A v1 config is decoded against this struct
+    // before migrate.ts passes `lsp` through untouched, so any field absent
+    // here is silently stripped and never reaches the LSP client.
+    timeout: Schema.optional(
+      Schema.Struct({
+        document: Schema.optional(Schema.Number),
+        full: Schema.optional(Schema.Number),
+      }),
+    ),
   }),
 ]).pipe((schema) => schema)
 
diff --git a/packages/opencode/src/lsp/client.ts b/packages/opencode/src/lsp/client.ts
index 08d8a53d9be0..2d9751543ab9 100644
--- a/packages/opencode/src/lsp/client.ts
+++ b/packages/opencode/src/lsp/client.ts
@@ -129,6 +129,13 @@ export async function create(input: {
 }) {
   const instance = input.instance
 
+  // Servers parsing very large translation units (e.g. clangd on an Unreal
+  // Engine codebase) can take far longer than the defaults to publish
+  // diagnostics. When the wait expires the client reports nothing, which is
+  // indistinguishable from a clean file, so allow per-server overrides.
+  const documentWaitTimeout = input.server.timeout?.document ?? DIAGNOSTICS_DOCUMENT_WAIT_TIMEOUT_MS
+  const fullWaitTimeout = input.server.timeout?.full ?? DIAGNOSTICS_FULL_WAIT_TIMEOUT_MS
+
   const connection = createMessageConnection(
     new StreamMessageReader(input.server.process.stdout as any),
     new StreamMessageWriter(input.server.process.stdin as any),
@@ -502,13 +509,13 @@ export async function create(input: {
       path: request.path,
       version: request.version,
       after: startedAt,
-      timeout: DIAGNOSTICS_DOCUMENT_WAIT_TIMEOUT_MS,
+      timeout: documentWaitTimeout,
     })
 
-    while (Date.now() - startedAt < DIAGNOSTICS_DOCUMENT_WAIT_TIMEOUT_MS) {
+    while (Date.now() - startedAt < documentWaitTimeout) {
       const result = await requestDocumentDiagnostics(request.path)
       if (result.matched) return
-      const remaining = DIAGNOSTICS_DOCUMENT_WAIT_TIMEOUT_MS - (Date.now() - startedAt)
+      const remaining = documentWaitTimeout - (Date.now() - startedAt)
       if (remaining <= 0) return
       const next = await Promise.race([
         pushWait.then((ready) => (ready ? "push" : ("timeout" as const))),
@@ -524,13 +531,13 @@ export async function create(input: {
       path: request.path,
       version: request.version,
       after: startedAt,
-      timeout: DIAGNOSTICS_FULL_WAIT_TIMEOUT_MS,
+      timeout: fullWaitTimeout,
     })
 
-    while (Date.now() - startedAt < DIAGNOSTICS_FULL_WAIT_TIMEOUT_MS) {
+    while (Date.now() - startedAt < fullWaitTimeout) {
       const result = await requestFullDiagnostics(request.path)
       if (result.handled || result.matched) return
-      const remaining = DIAGNOSTICS_FULL_WAIT_TIMEOUT_MS - (Date.now() - startedAt)
+      const remaining = fullWaitTimeout - (Date.now() - startedAt)
       if (remaining <= 0) return
       const next = await Promise.race([
         pushWait.then((ready) => (ready ? "push" : ("timeout" as const))),
diff --git a/packages/opencode/src/lsp/lsp.ts b/packages/opencode/src/lsp/lsp.ts
index 1ab3a0b82369..c7092d4967ce 100644
--- a/packages/opencode/src/lsp/lsp.ts
+++ b/packages/opencode/src/lsp/lsp.ts
@@ -176,6 +176,7 @@ const layer = Layer.effect(
                     env: { ...process.env, ...item.env },
                   }),
                   initialization: item.initialization,
+                  timeout: item.timeout,
                 }),
               }
             }
diff --git a/packages/opencode/src/lsp/server.ts b/packages/opencode/src/lsp/server.ts
index 2be68aa5a92d..146a1406ab7c 100644
--- a/packages/opencode/src/lsp/server.ts
+++ b/packages/opencode/src/lsp/server.ts
@@ -25,6 +25,10 @@ const output = (cmd: string[], opts: Process.RunOptions = {}) => Process.text(cm
 export interface Handle {
   process: ChildProcessWithoutNullStreams
   initialization?: Record<string, any>
+  timeout?: {
+    document?: number
+    full?: number
+  }
 }
 
 type RootFunction = (file: string, ctx: InstanceContext) => Promise<string | undefined>