diff --git a/.github/workflows/preview.yml b/.github/workflows/preview.yml
new file mode 100644
index 0000000..3d73f37
--- /dev/null
+++ b/.github/workflows/preview.yml
@@ -0,0 +1,162 @@
+name: Preview Release
+
+# Builds the `preview` channel on every push to main: a co-installable build
+# that tracks main, published to a rolling `preview` prerelease and the
+# `annot-preview` Homebrew formula. Stable releases are untouched (release.yml).
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+# A push supersedes any in-flight preview build, so the tap always reflects
+# the tip of main.
+concurrency:
+  group: preview-release
+  cancel-in-progress: true
+
+permissions:
+  contents: write
+
+jobs:
+  build-preview:
+    runs-on: macos-26 # Apple Silicon runner (Tahoe)
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0 # full history + tags, for the git-describe version
+
+      - name: Compute preview version
+        id: version
+        run: |
+          SHA=$(git rev-parse --short HEAD)
+          if LAST_TAG=$(git describe --tags --abbrev=0 --match 'v*' 2>/dev/null); then
+            BASE=${LAST_TAG#v}
+            COUNT=$(git rev-list --count "${LAST_TAG}..HEAD")
+          else
+            BASE="0.0.0"
+            COUNT=$(git rev-list --count HEAD)
+          fi
+          # Monotonic on COUNT (drives `brew upgrade`); SHA for traceability.
+          VERSION="${BASE}-preview.${COUNT}.g${SHA}"
+          echo "version=$VERSION" >> "$GITHUB_OUTPUT"
+          echo "sha=$SHA" >> "$GITHUB_OUTPUT"
+          echo "Preview version: $VERSION"
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v3
+        with:
+          version: 8
+
+      - name: Install Node dependencies
+        run: pnpm install
+
+      - name: Setup Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Rust cache
+        uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: src-tauri
+
+      - name: Import Apple certificate
+        env:
+          APPLE_CERTIFICATE: ${{ secrets.APPLE_CERTIFICATE }}
+          APPLE_CERTIFICATE_PASSWORD: ${{ secrets.APPLE_CERTIFICATE_PASSWORD }}
+        run: |
+          # Create temporary keychain
+          KEYCHAIN_PATH=$RUNNER_TEMP/app-signing.keychain-db
+          KEYCHAIN_PASSWORD=$(openssl rand -base64 32)
+
+          security create-keychain -p "$KEYCHAIN_PASSWORD" $KEYCHAIN_PATH
+          security set-keychain-settings -lut 21600 $KEYCHAIN_PATH
+          security unlock-keychain -p "$KEYCHAIN_PASSWORD" $KEYCHAIN_PATH
+
+          # Import certificate
+          echo "$APPLE_CERTIFICATE" | base64 --decode > $RUNNER_TEMP/certificate.p12
+          security import $RUNNER_TEMP/certificate.p12 -P "$APPLE_CERTIFICATE_PASSWORD" -A -t cert -f pkcs12 -k $KEYCHAIN_PATH
+          security set-key-partition-list -S apple-tool:,apple: -k "$KEYCHAIN_PASSWORD" $KEYCHAIN_PATH
+          security list-keychain -d user -s $KEYCHAIN_PATH
+
+      - name: Build Tauri app (preview channel)
+        env:
+          APPLE_SIGNING_IDENTITY: ${{ secrets.APPLE_SIGNING_IDENTITY }}
+          APPLE_ID: ${{ secrets.APPLE_ID }}
+          APPLE_PASSWORD: ${{ secrets.APPLE_PASSWORD }}
+          APPLE_TEAM_ID: ${{ secrets.APPLE_TEAM_ID }}
+          # Baked into the binary at compile time (see src-tauri/src/channel.rs).
+          ANNOT_CHANNEL: preview
+          ANNOT_BUILD_SHA: g${{ steps.version.outputs.sha }}
+        run: pnpm tauri build --config src-tauri/tauri.preview.conf.json
+
+      - name: Package artifact
+        run: |
+          cd src-tauri/target/release/bundle/macos
+          mkdir annot-preview
+          cp -R "annot (preview).app" annot-preview/
+          tar -czf annot-preview-darwin-arm64.tar.gz annot-preview
+          mv annot-preview-darwin-arm64.tar.gz "$GITHUB_WORKSPACE/"
+
+      - name: Publish rolling preview release
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # Delete + recreate so the `preview` tag and asset always point at
+          # the tip of main (Neovim's nightly pattern).
+          gh release delete preview --yes --cleanup-tag || true
+          gh release create preview \
+            --prerelease \
+            --target "$GITHUB_SHA" \
+            --title "Preview build (${{ steps.version.outputs.version }})" \
+            --notes "Rolling build from \`main\`. Install with \`brew install denolehov/tap/annot-preview\`." \
+            annot-preview-darwin-arm64.tar.gz
+
+      - name: Update annot-preview formula in tap
+        env:
+          TAP_TOKEN: ${{ secrets.HOMEBREW_TAP_TOKEN }}
+          VERSION: ${{ steps.version.outputs.version }}
+        run: |
+          SHA256=$(shasum -a 256 annot-preview-darwin-arm64.tar.gz | cut -d' ' -f1)
+          git clone "https://x-access-token:${TAP_TOKEN}@github.com/denolehov/homebrew-tap.git" tap
+          cat > tap/Formula/annot-preview.rb <<EOF
+          # typed: true
+          # frozen_string_literal: true
+
+          # Generated by annot's preview.yml workflow. DO NOT EDIT.
+          class AnnotPreview < Formula
+            desc "Human-in-the-loop annotation tool for AI workflows (preview channel)"
+            homepage "https://github.com/denolehov/annot"
+            version "${VERSION}"
+            url "https://github.com/denolehov/annot/releases/download/preview/annot-preview-darwin-arm64.tar.gz"
+            sha256 "${SHA256}"
+            license "AGPL-3.0"
+
+            depends_on :macos
+            depends_on arch: :arm64
+
+            def install
+              prefix.install "annot (preview).app"
+              bin.install_symlink prefix/"annot (preview).app/Contents/MacOS/annot-preview"
+            end
+
+            test do
+              system bin/"annot-preview", "--version"
+            end
+          end
+          EOF
+          cd tap
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git add Formula/annot-preview.rb
+          if git diff --staged --quiet; then
+            echo "Formula unchanged, nothing to commit."
+          else
+            git commit -m "chore: annot-preview ${VERSION}"
+            git push
+          fi
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index db84c5f..3e132b7 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -108,6 +108,9 @@ jobs:
 
   update-homebrew:
     needs: build-macos
+    # Skip prerelease tags (e.g. v1.2.3-rc.1) so they never overwrite the
+    # stable annot.rb formula. Preview builds use preview.yml + annot-preview.rb.
+    if: ${{ !contains(needs.build-macos.outputs.tag, '-') }}
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
diff --git a/scripts/make-preview-icon.py b/scripts/make-preview-icon.py
new file mode 100644
index 0000000..c3aaec7
--- /dev/null
+++ b/scripts/make-preview-icon.py
@@ -0,0 +1,44 @@
+# /// script
+# requires-python = ">=3.11"
+# dependencies = ["pillow"]
+# ///
+"""Derive the `annot (preview)` icon source from the stable icon.
+
+The stable icon is a colored-gradient rounded square with a white asterisk.
+Rotating the hue recolors the gradient while leaving the white mark untouched
+(white has zero saturation), so preview windows are recognisable at a glance
+without maintaining separate artwork.
+
+The output is a single source PNG; feed it to `tauri icon` to generate the
+full icon set (mirroring src-tauri/icons/):
+
+    uv run scripts/make-preview-icon.py /tmp/preview-src.png
+    pnpm tauri icon /tmp/preview-src.png --output src-tauri/icons-preview
+"""
+import sys
+import tempfile
+from pathlib import Path
+
+from PIL import Image
+
+ROOT = Path(__file__).resolve().parent.parent
+SRC = ROOT / "src-tauri" / "icons" / "icon.png"
+DST = (
+    Path(sys.argv[1])
+    if len(sys.argv) > 1
+    else Path(tempfile.gettempdir()) / "annot-preview-icon-source.png"
+)
+
+HUE_SHIFT_DEGREES = 120  # recolors green->blue, gold->magenta, purple->green
+
+img = Image.open(SRC).convert("RGBA")
+r, g, b, alpha = img.split()
+hue, sat, val = Image.merge("RGB", (r, g, b)).convert("HSV").split()
+shift = round(HUE_SHIFT_DEGREES / 360 * 256)
+hue = hue.point(lambda x: (x + shift) % 256)
+recolored = Image.merge("HSV", (hue, sat, val)).convert("RGB")
+out = Image.merge("RGBA", (*recolored.split(), alpha))
+
+DST.parent.mkdir(parents=True, exist_ok=True)
+out.save(DST)
+print(f"wrote {DST}")
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diff --git a/src-tauri/icons-preview/StoreLogo.png b/src-tauri/icons-preview/StoreLogo.png
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diff --git a/src-tauri/icons-preview/android/mipmap-anydpi-v26/ic_launcher.xml b/src-tauri/icons-preview/android/mipmap-anydpi-v26/ic_launcher.xml
new file mode 100644
index 0000000..2ffbf24
--- /dev/null
+++ b/src-tauri/icons-preview/android/mipmap-anydpi-v26/ic_launcher.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+  <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
+  <background android:drawable="@color/ic_launcher_background"/>
+</adaptive-icon>
\ No newline at end of file
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--- /dev/null
+++ b/src-tauri/icons-preview/android/values/ic_launcher_background.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+  <color name="ic_launcher_background">#fff</color>
+</resources>
\ No newline at end of file
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diff --git a/src-tauri/icons-preview/ios/AppIcon-83.5x83.5@2x.png b/src-tauri/icons-preview/ios/AppIcon-83.5x83.5@2x.png
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diff --git a/src-tauri/src/channel.rs b/src-tauri/src/channel.rs
new file mode 100644
index 0000000..792dc87
--- /dev/null
+++ b/src-tauri/src/channel.rs
@@ -0,0 +1,124 @@
+//! Release channel identity.
+//!
+//! annot ships two channels: `stable` (tagged releases) and `preview` (builds
+//! that track `main`). The channel is baked in at compile time from the
+//! `ANNOT_CHANNEL` and `ANNOT_BUILD_SHA` environment variables, which CI sets
+//! for preview builds. A normal local or release build leaves them unset and
+//! is therefore `stable` — behaviour is byte-identical to a build that never
+//! had this module.
+
+use std::sync::OnceLock;
+
+use serde::Serialize;
+
+/// Release channel this binary was built for.
+#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum Channel {
+    /// Tagged release build. The default for any build without CI overrides.
+    #[default]
+    Stable,
+    /// Build tracking `main`; carries the short commit SHA it was built from.
+    Preview(String),
+}
+
+/// Raw channel name baked in at compile time. `"stable"` unless CI overrides it.
+const CHANNEL: &str = match option_env!("ANNOT_CHANNEL") {
+    Some(c) => c,
+    None => "stable",
+};
+
+/// Short commit SHA this binary was built from. `"dev"` for local builds.
+const BUILD_SHA: &str = match option_env!("ANNOT_BUILD_SHA") {
+    Some(s) => s,
+    None => "dev",
+};
+
+/// The channel this binary was built for. Resolved once from compile-time env.
+pub fn current() -> &'static Channel {
+    static CURRENT: OnceLock<Channel> = OnceLock::new();
+    CURRENT.get_or_init(|| match CHANNEL {
+        "preview" => Channel::Preview(BUILD_SHA.to_string()),
+        _ => Channel::Stable,
+    })
+}
+
+impl Channel {
+    /// Whether this is a non-stable (preview) build.
+    pub fn is_preview(&self) -> bool {
+        matches!(self, Channel::Preview(_))
+    }
+
+    /// Human-facing application name. Preview builds carry a visible suffix so
+    /// stable and preview windows are distinguishable at a glance.
+    pub fn display_name(&self) -> &'static str {
+        match self {
+            Channel::Stable => "annot",
+            Channel::Preview(_) => "annot (preview)",
+        }
+    }
+
+    /// Config subdirectory name under the OS config dir. Preview gets its own
+    /// directory, isolated from stable's tags, exit modes, and bookmarks.
+    pub fn config_subdir(&self) -> &'static str {
+        match self {
+            Channel::Stable => "annot",
+            Channel::Preview(_) => "annot-preview",
+        }
+    }
+
+    /// Build marker for non-stable builds, e.g. `"preview · g1a2b3c"`.
+    /// `None` for stable, so stable output stays unchanged.
+    pub fn marker(&self) -> Option<String> {
+        match self {
+            Channel::Stable => None,
+            Channel::Preview(sha) => Some(format!("preview · {sha}")),
+        }
+    }
+}
+
+/// Full version string: the crate version, plus a channel marker for
+/// non-stable builds. Used by both `annot version` and clap's `--version`
+/// (which requires a `&'static str`), so the result is computed once and cached.
+pub fn version_string() -> &'static str {
+    static CACHE: OnceLock<String> = OnceLock::new();
+    CACHE
+        .get_or_init(|| match current().marker() {
+            Some(marker) => format!("{} ({})", env!("CARGO_PKG_VERSION"), marker),
+            None => env!("CARGO_PKG_VERSION").to_string(),
+        })
+        .as_str()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn stable_is_the_default() {
+        // The test binary compiles without ANNOT_CHANNEL set, so it is stable.
+        assert_eq!(*current(), Channel::Stable);
+        assert!(!current().is_preview());
+        assert_eq!(current().display_name(), "annot");
+        assert_eq!(current().config_subdir(), "annot");
+        assert_eq!(current().marker(), None);
+        assert_eq!(version_string(), env!("CARGO_PKG_VERSION"));
+    }
+
+    #[test]
+    fn channels_never_share_a_config_dir() {
+        // The isolation invariant, independent of which channel compiled this.
+        assert_ne!(
+            Channel::Stable.config_subdir(),
+            Channel::Preview(String::new()).config_subdir()
+        );
+    }
+
+    #[test]
+    fn preview_carries_sha_in_marker_and_name() {
+        let ch = Channel::Preview("g1a2b3c".to_string());
+        assert!(ch.is_preview());
+        assert_eq!(ch.marker(), Some("preview · g1a2b3c".to_string()));
+        assert_eq!(ch.display_name(), "annot (preview)");
+    }
+}
diff --git a/src-tauri/src/config.rs b/src-tauri/src/config.rs
index f820ee7..376ba76 100644
--- a/src-tauri/src/config.rs
+++ b/src-tauri/src/config.rs
@@ -158,9 +158,11 @@ fn save_merged<T: Mergeable + Serialize + DeserializeOwned>(
     Ok(())
 }
 
-/// Returns the config directory path: ~/.config/annot/ on Unix, %APPDATA%\annot\ on Windows.
+/// Returns the config directory path, e.g. `~/.config/annot/` on Unix or
+/// `%APPDATA%\annot\` on Windows. Preview builds resolve to an `annot-preview`
+/// subdirectory instead, keeping their config isolated from stable's.
 pub fn config_dir() -> Option<PathBuf> {
-    dirs::config_dir().map(|p| p.join("annot"))
+    dirs::config_dir().map(|p| p.join(crate::channel::current().config_subdir()))
 }
 
 /// Ensures the config directory exists.
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index 203f60a..4bef4a1 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -5,6 +5,7 @@ use parking_lot::Mutex;
 
 use tauri::WebviewWindowBuilder;
 
+pub mod channel;
 pub mod commands;
 pub mod config;
 pub mod diff;
@@ -140,7 +141,7 @@ pub fn run(state: AppState, context: tauri::Context, json_output: bool) {
                     "main",
                     tauri::WebviewUrl::App("index.html".into()),
                 )
-                .title("annot")
+                .title(channel::current().display_name())
                 .inner_size(1000.0, 700.0)
                 .visible(false); // Will be shown after content loads
                 #[cfg(target_os = "macos")]
diff --git a/src-tauri/src/main.rs b/src-tauri/src/main.rs
index 26740bd..e453e79 100644
--- a/src-tauri/src/main.rs
+++ b/src-tauri/src/main.rs
@@ -20,7 +20,7 @@ Examples:
 
 #[derive(Parser)]
 #[command(name = "annot")]
-#[command(version)]
+#[command(version = annot_lib::channel::version_string())]
 #[command(about = "Ephemeral annotation tool for AI workflows")]
 #[command(long_about = EXAMPLES)]
 struct Cli {
@@ -103,7 +103,7 @@ fn main() {
 
     // Handle version subcommand (doesn't need Tauri)
     if let Some(Command::Version) = cli.command {
-        println!("annot {}", env!("CARGO_PKG_VERSION"));
+        println!("annot {}", annot_lib::channel::version_string());
         return;
     }
 
diff --git a/src-tauri/src/mcp/mod.rs b/src-tauri/src/mcp/mod.rs
index d1de04b..b15ef1c 100644
--- a/src-tauri/src/mcp/mod.rs
+++ b/src-tauri/src/mcp/mod.rs
@@ -414,7 +414,7 @@ fn run_session_with_state(
 
     let builder = {
         let b = WebviewWindowBuilder::new(app_handle, &window_label, tauri::WebviewUrl::App("index.html".into()))
-            .title("annot")
+            .title(crate::channel::current().display_name())
             .inner_size(1000.0, 700.0)
             .visible(false); // Will be shown after content loads
         #[cfg(target_os = "macos")]
diff --git a/src-tauri/src/output/mod.rs b/src-tauri/src/output/mod.rs
index f467cd8..2271d06 100644
--- a/src-tauri/src/output/mod.rs
+++ b/src-tauri/src/output/mod.rs
@@ -13,6 +13,7 @@ mod snapshot_tests;
 
 use std::collections::{BTreeMap, HashMap};
 
+use crate::channel::Channel;
 use crate::lang;
 use crate::mcp::tools::SessionImage;
 use crate::portal::LoadedPortal;
@@ -56,11 +57,14 @@ pub struct FormatMetadata {
     pub general_comment_count: usize,
     pub terraform_count: usize,
     pub bookmark_count: usize,
+    /// Release channel this build belongs to. `Stable` on release builds, so
+    /// stable output is unaffected; `Preview(sha)` carries the build's SHA.
+    pub channel: Channel,
 }
 
 /// Serialize a FormatResult as JSON for `--json` CLI output.
 pub fn format_json(result: &FormatResult) -> String {
-    let json = serde_json::json!({
+    let mut json = serde_json::json!({
         "text": result.text,
         "images": result.images.iter().map(|img| serde_json::json!({
             "figure": img.figure,
@@ -74,6 +78,11 @@ pub fn format_json(result: &FormatResult) -> String {
         "terraform_count": result.metadata.terraform_count,
         "bookmark_count": result.metadata.bookmark_count,
     });
+    // Only non-stable builds carry a `channel` key, so stable JSON is unchanged.
+    if result.metadata.channel.is_preview() {
+        json["channel"] = serde_json::to_value(&result.metadata.channel)
+            .expect("Channel JSON serialization should not fail");
+    }
     serde_json::to_string(&json).expect("FormatResult JSON serialization should not fail")
 }
 
@@ -398,6 +407,13 @@ pub fn format_output(review: &Review, mode: OutputMode) -> FormatResult {
     let builder_mode = calculate_builder_mode(content, max_line);
     let mut out = OutputBuilder::new(builder_mode);
 
+    // Non-stable builds announce themselves so feedback is traceable to a
+    // specific build. Stable adds nothing here, keeping its output unchanged.
+    if let Some(marker) = crate::channel::current().marker() {
+        out.raw_line(&format!("[annot {marker}]"));
+        out.blank_line();
+    }
+
     // TAGS block (if any tags are used)
     let unique_tags = collect_unique_tags(review);
     if !unique_tags.is_empty() {
@@ -601,6 +617,7 @@ pub fn format_output(review: &Review, mode: OutputMode) -> FormatResult {
             general_comment_count,
             terraform_count,
             bookmark_count,
+            channel: crate::channel::current().clone(),
         },
     }
 }
diff --git a/src-tauri/tauri.preview.conf.json b/src-tauri/tauri.preview.conf.json
new file mode 100644
index 0000000..b43cd39
--- /dev/null
+++ b/src-tauri/tauri.preview.conf.json
@@ -0,0 +1,14 @@
+{
+  "productName": "annot (preview)",
+  "identifier": "com.denolehov.annot.preview",
+  "mainBinaryName": "annot-preview",
+  "bundle": {
+    "icon": [
+      "icons-preview/32x32.png",
+      "icons-preview/128x128.png",
+      "icons-preview/128x128@2x.png",
+      "icons-preview/icon.icns",
+      "icons-preview/icon.ico"
+    ]
+  }
+}