diff --git a/packages/app/src/components/prompt-input/submit.test.ts b/packages/app/src/components/prompt-input/submit.test.ts
index 83b6212dcc..d99516e591 100644
--- a/packages/app/src/components/prompt-input/submit.test.ts
+++ b/packages/app/src/components/prompt-input/submit.test.ts
@@ -18,6 +18,7 @@ const optimistic: Array<{
 const optimisticSeeded: boolean[] = []
 const storedSessions: Record<string, Array<{ id: string; title?: string }>> = {}
 const promoted: Array<{ directory: string; sessionID: string }> = []
+const sentSummaries: Array<{ sessionID: string; instructions?: string }> = []
 const sentShell: string[] = []
 const syncedDirectories: string[] = []
 
@@ -25,7 +26,7 @@ let params: { id?: string } = {}
 let selected = "/repo/worktree-a"
 let variant: string | undefined
 
-const promptValue: Prompt = [{ type: "text", content: "ls", start: 0, end: 2 }]
+let promptValue: Prompt = [{ type: "text", content: "ls", start: 0, end: 2 }]
 
 const clientFor = (directory: string) => {
   createdClients.push(directory)
@@ -47,6 +48,10 @@ const clientFor = (directory: string) => {
       prompt: async () => ({ data: undefined }),
       promptAsync: async () => ({ data: undefined }),
       command: async () => ({ data: undefined }),
+      summarize: async (input: { sessionID: string; instructions?: string }) => {
+        sentSummaries.push({ sessionID: input.sessionID, instructions: input.instructions })
+        return { data: undefined }
+      },
       abort: async () => ({ data: undefined }),
     },
     worktree: {
@@ -208,6 +213,8 @@ beforeEach(() => {
   optimistic.length = 0
   optimisticSeeded.length = 0
   promoted.length = 0
+  promptValue = [{ type: "text", content: "ls", start: 0, end: 2 }]
+  sentSummaries.length = 0
   params = {}
   sentShell.length = 0
   syncedDirectories.length = 0
@@ -342,4 +349,31 @@ describe("prompt submit worktree selection", () => {
     expect(storedSessions["/repo/worktree-a"]).toEqual([{ id: "session-1", title: "New session 1" }])
     expect(optimisticSeeded).toEqual([true])
   })
+
+  test("submits typed compact slash arguments as summarize instructions", async () => {
+    params = { id: "session-1" }
+    promptValue = [{ type: "text", content: "/compact keep unresolved TODOs", start: 0, end: 30 }]
+
+    const submit = createPromptSubmit({
+      info: () => ({ id: "session-1" }),
+      imageAttachments: () => [],
+      commentCount: () => 0,
+      autoAccept: () => false,
+      mode: () => "normal",
+      working: () => false,
+      editor: () => undefined,
+      queueScroll: () => undefined,
+      promptLength: (value) => value.reduce((sum, part) => sum + ("content" in part ? part.content.length : 0), 0),
+      addToHistory: () => undefined,
+      resetHistoryNavigation: () => undefined,
+      setMode: () => undefined,
+      setPopover: () => undefined,
+      onSubmit: () => undefined,
+    })
+
+    await submit.handleSubmit({ preventDefault: () => undefined } as unknown as Event)
+
+    expect(sentSummaries).toEqual([{ sessionID: "session-1", instructions: "keep unresolved TODOs" }])
+    expect(optimistic).toHaveLength(0)
+  })
 })
diff --git a/packages/app/src/components/prompt-input/submit.ts b/packages/app/src/components/prompt-input/submit.ts
index 05f0a3ed2c..d127fccbe0 100644
--- a/packages/app/src/components/prompt-input/submit.ts
+++ b/packages/app/src/components/prompt-input/submit.ts
@@ -50,6 +50,21 @@ const draftText = (prompt: Prompt) => prompt.map((part) => ("content" in part ?
 
 const draftImages = (prompt: Prompt) => prompt.filter((part): part is ImageAttachmentPart => part.type === "image")
 
+const slashCommand = (text: string) => {
+  if (!text.startsWith("/")) return undefined
+  return text.split("\n")[0].split(" ")[0].slice(1)
+}
+
+const slashArguments = (text: string) => {
+  const firstLineEnd = text.indexOf("\n")
+  const firstLine = firstLineEnd === -1 ? text : text.slice(0, firstLineEnd)
+  const [, ...firstLineArgs] = firstLine.split(" ")
+  const restOfInput = firstLineEnd === -1 ? "" : text.slice(firstLineEnd + 1)
+  return firstLineArgs.join(" ") + (restOfInput ? "\n" + restOfInput : "")
+}
+
+const isCompactSlash = (command: string | undefined) => command === "compact" || command === "summarize"
+
 export async function sendFollowupDraft(input: FollowupSendInput) {
   const text = draftText(input.draft.prompt)
   const images = draftImages(input.draft.prompt)
@@ -71,8 +86,27 @@ export async function sendFollowupDraft(input: FollowupSendInput) {
     return true
   }
 
-  const [head, ...tail] = text.split(" ")
-  const cmd = head?.startsWith("/") ? head.slice(1) : undefined
+  const cmd = slashCommand(text)
+  if (isCompactSlash(cmd)) {
+    setBusy()
+    try {
+      if (!(await wait())) {
+        setIdle()
+        return false
+      }
+
+      const instructions = slashArguments(text).trim()
+      const payload = instructions
+        ? { sessionID: input.draft.sessionID, ...input.draft.model, instructions }
+        : { sessionID: input.draft.sessionID, ...input.draft.model }
+      await input.client.session.summarize(payload)
+      return true
+    } catch (err) {
+      setIdle()
+      throw err
+    }
+  }
+
   if (cmd && input.sync.data.command.find((item) => item.name === cmd)) {
     setBusy()
     try {
@@ -84,7 +118,7 @@ export async function sendFollowupDraft(input: FollowupSendInput) {
       await input.client.session.command({
         sessionID: input.draft.sessionID,
         command: cmd,
-        arguments: tail.join(" "),
+        arguments: slashArguments(text),
         agent: input.draft.agent,
         model: `${input.draft.model.providerID}/${input.draft.model.modelID}`,
         variant: input.draft.variant,
@@ -453,8 +487,7 @@ export function createPromptSubmit(input: PromptSubmitInput) {
     }
 
     if (text.startsWith("/")) {
-      const [cmdName, ...args] = text.split(" ")
-      const commandName = cmdName.slice(1)
+      const commandName = slashCommand(text) ?? ""
       const customCommand = sync.data.command.find((c) => c.name === commandName)
       if (customCommand) {
         clearInput()
@@ -462,7 +495,7 @@ export function createPromptSubmit(input: PromptSubmitInput) {
           .command({
             sessionID: session.id,
             command: commandName,
-            arguments: args.join(" "),
+            arguments: slashArguments(text),
             agent,
             model: `${model.providerID}/${model.modelID}`,
             variant,
@@ -483,6 +516,22 @@ export function createPromptSubmit(input: PromptSubmitInput) {
           })
         return
       }
+
+      if (isCompactSlash(commandName)) {
+        clearInput()
+        const instructions = slashArguments(text).trim()
+        const payload = instructions
+          ? { sessionID: session.id, ...model, instructions }
+          : { sessionID: session.id, ...model }
+        client.session.summarize(payload).catch((err) => {
+          showToast({
+            title: language.t("prompt.toast.promptSendFailed.title"),
+            description: errorMessage(err),
+          })
+          restoreInput()
+        })
+        return
+      }
     }
 
     const commentItems = context.filter((item) => item.type === "file" && !!item.comment?.trim())
diff --git a/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx b/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
index f4b11fa465..b7f911ecbd 100644
--- a/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
@@ -1143,6 +1143,21 @@ export function Prompt(props: PromptProps) {
         command: inputText,
       })
       setStore("mode", "normal")
+    } else if (isCompactSlash(inputText)) {
+      const instructions = slashArguments(inputText).trim()
+      const payload = instructions
+        ? {
+            sessionID,
+            modelID: selectedModel.modelID,
+            providerID: selectedModel.providerID,
+            instructions,
+          }
+        : {
+            sessionID,
+            modelID: selectedModel.modelID,
+            providerID: selectedModel.providerID,
+          }
+      void sdk.client.session.summarize(payload)
     } else if (
       inputText.startsWith("/") &&
       iife(() => {
@@ -1220,6 +1235,19 @@ export function Prompt(props: PromptProps) {
     input.clear()
     return true
   }
+
+  function isCompactSlash(text: string) {
+    const command = text.split("\n")[0].split(" ")[0].slice(1)
+    return text.startsWith("/") && (command === "compact" || command === "summarize")
+  }
+
+  function slashArguments(text: string) {
+    const firstLineEnd = text.indexOf("\n")
+    const firstLine = firstLineEnd === -1 ? text : text.slice(0, firstLineEnd)
+    const [, ...firstLineArgs] = firstLine.split(" ")
+    const restOfInput = firstLineEnd === -1 ? "" : text.slice(firstLineEnd + 1)
+    return firstLineArgs.join(" ") + (restOfInput ? "\n" + restOfInput : "")
+  }
   const exit = useExit()
 
   function pasteText(text: string, virtualText: string) {
diff --git a/packages/opencode/src/server/routes/instance/httpapi/groups/session.ts b/packages/opencode/src/server/routes/instance/httpapi/groups/session.ts
index b8c8a142be..314aaba6b2 100644
--- a/packages/opencode/src/server/routes/instance/httpapi/groups/session.ts
+++ b/packages/opencode/src/server/routes/instance/httpapi/groups/session.ts
@@ -62,6 +62,7 @@ export const SummarizePayload = Schema.Struct({
   providerID: ProviderID,
   modelID: ModelID,
   auto: Schema.optional(Schema.Boolean),
+  instructions: Schema.optional(Schema.String),
 })
 export const PromptPayload = Schema.Struct(Struct.omit(SessionPrompt.PromptInput.fields, ["sessionID"]))
 export const CommandPayload = Schema.Struct(Struct.omit(SessionPrompt.CommandInput.fields, ["sessionID"]))
diff --git a/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts b/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts
index 2e3617d146..8096dcb470 100644
--- a/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts
+++ b/packages/opencode/src/server/routes/instance/httpapi/handlers/session.ts
@@ -277,6 +277,7 @@ export const sessionHandlers = HttpApiBuilder.group(InstanceHttpApi, "session",
           modelID: ctx.payload.modelID,
         },
         auto: ctx.payload.auto ?? false,
+        instructions: ctx.payload.instructions,
       })
       yield* promptSvc.loop({ sessionID: ctx.params.sessionID })
       return true
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
index ef007fe74d..ae5382e7b9 100644
--- a/packages/opencode/src/session/compaction.ts
+++ b/packages/opencode/src/session/compaction.ts
@@ -133,6 +133,12 @@ function buildPrompt(input: { previousSummary?: string; context: string[] }) {
   return [anchor, SUMMARY_TEMPLATE, ...input.context].join("\n\n")
 }
 
+function withInstructions(prompt: string, instructions: string | undefined) {
+  const trimmed = instructions?.trim()
+  if (!trimmed) return prompt
+  return [prompt, "Additional user instructions for this compaction:", trimmed].join("\n\n")
+}
+
 function preserveRecentBudget(input: { cfg: Config.Info; model: Provider.Model }) {
   return (
     input.cfg.compaction?.preserve_recent_tokens ??
@@ -202,6 +208,7 @@ export interface Interface {
     model: { providerID: ProviderID; modelID: ModelID }
     auto: boolean
     overflow?: boolean
+    instructions?: string
   }) => Effect.Effect<void>
 }
 
@@ -400,7 +407,10 @@ export const layer = Layer.effect(
         { sessionID: input.sessionID },
         { context: [], prompt: undefined },
       )
-      const nextPrompt = compacting.prompt ?? buildPrompt({ previousSummary, context: compacting.context })
+      const nextPrompt = withInstructions(
+        compacting.prompt ?? buildPrompt({ previousSummary, context: compacting.context }),
+        compactionPart?.instructions,
+      )
       const msgs = structuredClone(selected.head)
       yield* plugin.trigger("experimental.chat.messages.transform", {}, { messages: msgs })
       const modelMessages = yield* MessageV2.toModelMessagesEffect(msgs, model, {
@@ -587,6 +597,7 @@ export const layer = Layer.effect(
       model: { providerID: ProviderID; modelID: ModelID }
       auto: boolean
       overflow?: boolean
+      instructions?: string
     }) {
       const msg = yield* session.updateMessage({
         id: MessageID.ascending(),
@@ -603,6 +614,7 @@ export const layer = Layer.effect(
         type: "compaction",
         auto: input.auto,
         overflow: input.overflow,
+        instructions: input.instructions,
       })
       if (flags.experimentalEventSystem) {
         yield* events.publish(SessionEvent.Compaction.Started, {
diff --git a/packages/opencode/src/session/message-v2.ts b/packages/opencode/src/session/message-v2.ts
index 2745ff4f45..827d761967 100644
--- a/packages/opencode/src/session/message-v2.ts
+++ b/packages/opencode/src/session/message-v2.ts
@@ -186,6 +186,7 @@ export const CompactionPart = Schema.Struct({
   type: Schema.Literal("compaction"),
   auto: Schema.Boolean,
   overflow: Schema.optional(Schema.Boolean),
+  instructions: Schema.optional(Schema.String),
   tail_start_id: Schema.optional(MessageID),
 }).annotate({ identifier: "CompactionPart" })
 export type CompactionPart = Types.DeepMutable<Schema.Schema.Type<typeof CompactionPart>>
diff --git a/packages/opencode/test/session/compaction.test.ts b/packages/opencode/test/session/compaction.test.ts
index 55ddc621ca..310712df4a 100644
--- a/packages/opencode/test/session/compaction.test.ts
+++ b/packages/opencode/test/session/compaction.test.ts
@@ -287,8 +287,8 @@ function compactionProcessLayer(options?: CompactionProcessOptions) {
   )
 }
 
-function createSummaryCompaction(sessionID: SessionID) {
-  return SessionCompaction.use.create({ sessionID, agent: "build", model: ref, auto: false })
+function createSummaryCompaction(sessionID: SessionID, instructions?: string) {
+  return SessionCompaction.use.create({ sessionID, agent: "build", model: ref, auto: false, instructions })
 }
 
 function readCompactionPart(sessionID: SessionID) {
@@ -959,6 +959,30 @@ describe("session.compaction.process", () => {
     }).pipe(withCompaction({ config: cfg({ tail_turns: 2, preserve_recent_tokens: 100 }) })),
   )
 
+  itCompaction.instance(
+    "appends stored instructions to compaction prompt",
+    () => {
+      const stub = llm()
+      let captured = ""
+      stub.push(reply("summary", (input) => (captured = JSON.stringify(input.messages))))
+      return Effect.gen(function* () {
+        const ssn = yield* SessionNs.Service
+        const session = yield* ssn.create({})
+        yield* createUserMessage(session.id, "first")
+        yield* createSummaryCompaction(session.id, "focus on unresolved TODOs")
+
+        const msgs = yield* ssn.messages({ sessionID: session.id })
+        const parent = msgs.at(-1)?.info.id
+        expect(parent).toBeTruthy()
+        yield* SessionCompaction.use.process({ parentID: parent!, messages: msgs, sessionID: session.id, auto: false })
+
+        expect(captured).toContain("Additional user instructions for this compaction")
+        expect(captured).toContain("focus on unresolved TODOs")
+      }).pipe(withCompaction({ llm: stub.layer }))
+    },
+    { git: true },
+  )
+
   itCompaction.instance(
     "falls back to full summary when even one recent turn exceeds preserve token budget",
     () => {