diff --git a/packages/opencode/src/cli/cmd/run.ts b/packages/opencode/src/cli/cmd/run.ts
index 54248f96f3..0a7f0b716a 100644
--- a/packages/opencode/src/cli/cmd/run.ts
+++ b/packages/opencode/src/cli/cmd/run.ts
@@ -50,6 +50,11 @@ export const RunCommand = cmd({
         describe: "session id to continue",
         type: "string",
       })
+      .option("fork-session", {
+        alias: ["fork"],
+        describe: "fork the session before continuing (requires --continue or --session)",
+        type: "boolean",
+      })
       .option("share", {
         type: "boolean",
         describe: "share the session",
@@ -133,6 +138,11 @@ export const RunCommand = cmd({
       process.exit(1)
     }
 
+    if (args.forkSession && !args.continue && !args.session) {
+      UI.error("--fork-session requires --continue or --session")
+      process.exit(1)
+    }
+
     const execute = async (sdk: OpencodeClient, sessionID: string) => {
       const printEvent = (color: string, type: string, title: string) => {
         UI.println(
@@ -279,11 +289,16 @@ export const RunCommand = cmd({
       const sdk = createOpencodeClient({ baseUrl: args.attach })
 
       const sessionID = await (async () => {
-        if (args.continue) {
-          const result = await sdk.session.list()
-          return result.data?.find((s) => !s.parentID)?.id
+        const baseID = args.continue
+          ? (await sdk.session.list()).data?.find((s) => !s.parentID)?.id
+          : args.session
+
+        if (baseID && args.forkSession) {
+          const forked = await sdk.session.fork({ sessionID: baseID })
+          return forked.data?.id
         }
-        if (args.session) return args.session
+
+        if (baseID) return baseID
 
         const title =
           args.title !== undefined
@@ -354,11 +369,16 @@ export const RunCommand = cmd({
       }
 
       const sessionID = await (async () => {
-        if (args.continue) {
-          const result = await sdk.session.list()
-          return result.data?.find((s) => !s.parentID)?.id
+        const baseID = args.continue
+          ? (await sdk.session.list()).data?.find((s) => !s.parentID)?.id
+          : args.session
+
+        if (baseID && args.forkSession) {
+          const forked = await sdk.session.fork({ sessionID: baseID })
+          return forked.data?.id
         }
-        if (args.session) return args.session
+
+        if (baseID) return baseID
 
         const title =
           args.title !== undefined
diff --git a/packages/opencode/src/cli/cmd/tui/app.tsx b/packages/opencode/src/cli/cmd/tui/app.tsx
index 713def2e5a..11334bed83 100644
--- a/packages/opencode/src/cli/cmd/tui/app.tsx
+++ b/packages/opencode/src/cli/cmd/tui/app.tsx
@@ -249,7 +249,8 @@ function App() {
           })
         local.model.set({ providerID, modelID }, { recent: true })
       }
-      if (args.sessionID) {
+      // Handle --session without --fork immediately (fork is handled in createEffect below)
+      if (args.sessionID && !args.fork) {
         route.navigate({
           type: "session",
           sessionID: args.sessionID,
@@ -267,10 +268,36 @@ function App() {
       .find((x) => x.parentID === undefined)?.id
     if (match) {
       continued = true
-      route.navigate({ type: "session", sessionID: match })
+      if (args.fork) {
+        sdk.client.session.fork({ sessionID: match }).then((result) => {
+          if (result.data?.id) {
+            route.navigate({ type: "session", sessionID: result.data.id })
+          } else {
+            toast.show({ message: "Failed to fork session", variant: "error" })
+          }
+        })
+      } else {
+        route.navigate({ type: "session", sessionID: match })
+      }
     }
   })
 
+  // Handle --session with --fork: wait for sync to be fully complete before forking
+  // (session list loads in non-blocking phase for --session, so we must wait for "complete"
+  // to avoid a race where reconcile overwrites the newly forked session)
+  let forked = false
+  createEffect(() => {
+    if (forked || sync.status !== "complete" || !args.sessionID || !args.fork) return
+    forked = true
+    sdk.client.session.fork({ sessionID: args.sessionID }).then((result) => {
+      if (result.data?.id) {
+        route.navigate({ type: "session", sessionID: result.data.id })
+      } else {
+        toast.show({ message: "Failed to fork session", variant: "error" })
+      }
+    })
+  })
+
   createEffect(
     on(
       () => sync.status === "complete" && sync.data.provider.length === 0,
diff --git a/packages/opencode/src/cli/cmd/tui/context/args.tsx b/packages/opencode/src/cli/cmd/tui/context/args.tsx
index ffd43009a4..8a229ffaba 100644
--- a/packages/opencode/src/cli/cmd/tui/context/args.tsx
+++ b/packages/opencode/src/cli/cmd/tui/context/args.tsx
@@ -6,6 +6,7 @@ export interface Args {
   prompt?: string
   continue?: boolean
   sessionID?: string
+  fork?: boolean
 }
 
 export const { use: useArgs, provider: ArgsProvider } = createSimpleContext({
diff --git a/packages/opencode/src/cli/cmd/tui/thread.ts b/packages/opencode/src/cli/cmd/tui/thread.ts
index 0571426854..8d7c0bd679 100644
--- a/packages/opencode/src/cli/cmd/tui/thread.ts
+++ b/packages/opencode/src/cli/cmd/tui/thread.ts
@@ -64,6 +64,11 @@ export const TuiThreadCommand = cmd({
         type: "string",
         describe: "session id to continue",
       })
+      .option("fork-session", {
+        alias: ["fork"],
+        type: "boolean",
+        describe: "fork the session when continuing (use with --continue or --session)",
+      })
       .option("prompt", {
         type: "string",
         describe: "prompt to use",
@@ -73,6 +78,11 @@ export const TuiThreadCommand = cmd({
         describe: "agent to use",
       }),
   handler: async (args) => {
+    if (args.forkSession && !args.continue && !args.session) {
+      UI.error("--fork-session requires --continue or --session")
+      process.exit(1)
+    }
+
     // Resolve relative paths against PWD to preserve behavior when using --cwd flag
     const baseCwd = process.env.PWD ?? process.cwd()
     const cwd = args.project ? path.resolve(baseCwd, args.project) : process.cwd()
@@ -150,6 +160,7 @@ export const TuiThreadCommand = cmd({
         agent: args.agent,
         model: args.model,
         prompt,
+        fork: args.forkSession,
       },
       onExit: async () => {
         await client.call("shutdown", undefined)