diff --git a/README.md b/README.md
index 9592158..8f592c5 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,7 @@ Integrate the [opencode](https://github.com/sst/opencode) AI assistant with Neov
 - Respond to permission requests.
 - Reload edited buffers in real-time.
 - Monitor state via statusline component.
+- Diff changes across entire sessions using `codediff.nvim`.
 - Forward Server-Sent-Events as autocmds for automation.
 - Sensible defaults with well-documented, flexible configuration and API to fit your workflow.
 - _Vim-y_ — supports ranges and dot-repeat.
@@ -262,6 +263,7 @@ Select from all `opencode.nvim` functionality.
 - Prompts
 - Commands
   - Fetches custom commands from `opencode`
+- Session diffs (requires `codediff.nvim`)
 - Provider controls
 
 Highlights and previews items when using `snacks.picker`.
@@ -301,6 +303,13 @@ Command `opencode`:
 | `prompt.clear`           | Clear the TUI input                                |
 | `agent.cycle`            | Cycle the selected agent                           |
 
+### 🔍 Session Diff — `require("opencode").session_diff()`
+
+View all changes made during an `opencode` session.
+
+- Pick from a list of sessions (sorted by recent activity).
+- Exports session snapshots and displays differences using [`codediff.nvim`](https://github.com/esmuellert/codediff.nvim).
+
 ## 👀 Events
 
 `opencode.nvim` forwards `opencode`'s Server-Sent-Events as an `OpencodeEvent` autocmd:
diff --git a/lua/opencode.lua b/lua/opencode.lua
index 1e6880b..cbf23e3 100644
--- a/lua/opencode.lua
+++ b/lua/opencode.lua
@@ -12,6 +12,8 @@ M.toggle = require("opencode.provider").toggle
 M.start = require("opencode.provider").start
 M.stop = require("opencode.provider").stop
 
+M.session_diff = require("opencode.diff").session_diff
+
 M.statusline = require("opencode.status").statusline
 
 return M
diff --git a/lua/opencode/cli/client.lua b/lua/opencode/cli/client.lua
index 8553065..25a1696 100644
--- a/lua/opencode/cli/client.lua
+++ b/lua/opencode/cli/client.lua
@@ -214,6 +214,24 @@ function M.get_commands(port, callback)
   M.call(port, "/command", "GET", nil, callback)
 end
 
+---@class opencode.cli.client.Session
+---@field id string
+---@field slug string
+---@field version string
+---@field projectID string
+---@field directory string
+---@field title string
+---@field time { created: number, updated: number }
+---@field summary { additions: number, deletions: number, files: number }
+
+---Get all sessions from `opencode`.
+---
+---@param port number
+---@param callback fun(sessions: opencode.cli.client.Session[])
+function M.get_sessions(port, callback)
+  M.call(port, "/session", "GET", nil, callback)
+end
+
 ---@class opencode.cli.client.PathResponse
 ---@field directory string
 ---@field worktree string
diff --git a/lua/opencode/config.lua b/lua/opencode/config.lua
index 2b1a3d7..7fffa96 100644
--- a/lua/opencode/config.lua
+++ b/lua/opencode/config.lua
@@ -18,6 +18,9 @@ vim.g.opencode_opts = vim.g.opencode_opts
 ---If set, `opencode.nvim` will append `--port <port>` to `provider.cmd`.
 ---@field port? number
 ---
+---The data directory where `opencode` stores its data.
+---@field diff_data_dir? string
+---
 ---Contexts to inject into prompts, keyed by their placeholder.
 ---@field contexts? table<string, fun(context: opencode.Context): string|nil>
 ---
@@ -45,6 +48,7 @@ vim.g.opencode_opts = vim.g.opencode_opts
 ---@type opencode.Opts
 local defaults = {
   port = nil,
+  diff_data_dir = "~/.local/share/opencode",
   -- stylua: ignore
   contexts = {
     ["@this"] = function(context) return context:this() end,
@@ -98,6 +102,7 @@ local defaults = {
         ["prompt.submit"] = "Submit the current prompt",
         ["prompt.clear"] = "Clear the current prompt",
       },
+      diff = true,
       provider = true,
     },
     snacks = {
diff --git a/lua/opencode/diff.lua b/lua/opencode/diff.lua
new file mode 100644
index 0000000..a799e83
--- /dev/null
+++ b/lua/opencode/diff.lua
@@ -0,0 +1,275 @@
+---Session diff functionality for opencode.nvim
+---Uses codediff.nvim to display diffs between session snapshots.
+local M = {}
+local data_dir = vim.fn.expand(require("opencode.config").opts.diff_data_dir)
+
+---@class opencode.diff.Snapshots
+---@field first string|nil First snapshot hash (step-start)
+---@field last string|nil Last snapshot hash (step-finish)
+---@field project_id string|nil Project ID for the session
+
+---Read JSON file and parse it
+---@param path string
+---@return table|nil
+local function read_json(path)
+  local file = io.open(path, "r")
+  if not file then
+    return nil
+  end
+  local content = file:read("*a")
+  file:close()
+  local ok, data = pcall(vim.fn.json_decode, content)
+  if ok then
+    return data
+  end
+  return nil
+end
+
+---Get list of message IDs for a session (sorted)
+---@param session_id string
+---@return string[]
+local function get_message_ids(session_id)
+  local msg_dir = data_dir .. "/storage/message/" .. session_id
+  local handle = vim.uv.fs_scandir(msg_dir)
+  if not handle then
+    return {}
+  end
+
+  local messages = {}
+  while true do
+    local name, ftype = vim.uv.fs_scandir_next(handle)
+    if not name then
+      break
+    end
+    if ftype == "file" and name:match("%.json$") then
+      local msg_id = name:gsub("%.json$", "")
+      table.insert(messages, msg_id)
+    end
+  end
+
+  table.sort(messages)
+  return messages
+end
+
+---Get snapshots from part files for a message
+---@param msg_id string
+---@return { step_starts: string[], step_finishes: string[] }
+local function get_message_snapshots(msg_id)
+  local part_dir = data_dir .. "/storage/part/" .. msg_id
+  local handle = vim.uv.fs_scandir(part_dir)
+  if not handle then
+    return { step_starts = {}, step_finishes = {} }
+  end
+
+  local step_starts = {}
+  local step_finishes = {}
+
+  -- Collect all part files
+  local parts = {}
+  while true do
+    local name, ftype = vim.uv.fs_scandir_next(handle)
+    if not name then
+      break
+    end
+    if ftype == "file" and name:match("%.json$") then
+      table.insert(parts, name)
+    end
+  end
+  table.sort(parts)
+
+  for _, part_name in ipairs(parts) do
+    local part_file = part_dir .. "/" .. part_name
+    local data = read_json(part_file)
+    if data and data.snapshot then
+      if data.type == "step-start" then
+        table.insert(step_starts, data.snapshot)
+      elseif data.type == "step-finish" then
+        table.insert(step_finishes, data.snapshot)
+      end
+    end
+  end
+
+  return { step_starts = step_starts, step_finishes = step_finishes }
+end
+
+---Find snapshots for session-wide diff
+---@param session_id string
+---@param project_id string
+---@return opencode.diff.Snapshots
+local function find_session_snapshots(session_id, project_id)
+  local messages = get_message_ids(session_id)
+  local first = nil
+  local last = nil
+
+  for _, msg_id in ipairs(messages) do
+    local snaps = get_message_snapshots(msg_id)
+
+    -- First step-start across all messages
+    if not first and #snaps.step_starts > 0 then
+      first = snaps.step_starts[1]
+    end
+
+    -- Last step-finish across all messages
+    if #snaps.step_finishes > 0 then
+      last = snaps.step_finishes[#snaps.step_finishes]
+    end
+  end
+
+  return {
+    first = first,
+    last = last,
+    project_id = project_id,
+  }
+end
+
+---Export a git tree to a temporary directory
+---@param snapshot_git string Path to the snapshot git directory
+---@param tree_hash string Git tree hash
+---@param callback fun(err: string|nil, temp_dir: string|nil)
+local function export_tree(snapshot_git, tree_hash, callback)
+  -- Create temp directory
+  local temp_dir = vim.fn.tempname()
+  vim.fn.mkdir(temp_dir, "p")
+
+  -- Verify the object exists
+  vim.system({ "git", "--git-dir=" .. snapshot_git, "cat-file", "-t", tree_hash }, { text = true }, function(result)
+    if result.code ~= 0 then
+      vim.schedule(function()
+        callback("Snapshot object no longer exists (may have been garbage collected): " .. tree_hash, nil)
+      end)
+      return
+    end
+
+    -- Export the tree using git archive
+    vim.system({ "git", "--git-dir=" .. snapshot_git, "archive", tree_hash }, { text = false }, function(archive_result)
+      if archive_result.code ~= 0 then
+        vim.schedule(function()
+          callback("Failed to archive tree: " .. (archive_result.stderr or ""), nil)
+        end)
+        return
+      end
+
+      -- Extract the archive
+      vim.system(
+        { "tar", "-xf", "-", "-C", temp_dir },
+        { stdin = archive_result.stdout, text = false },
+        function(tar_result)
+          vim.schedule(function()
+            if tar_result.code ~= 0 then
+              callback("Failed to extract archive: " .. (tar_result.stderr or ""), nil)
+            else
+              callback(nil, temp_dir)
+            end
+          end)
+        end
+      )
+    end)
+  end)
+end
+
+---Show diff between two snapshots using codediff.nvim
+---@param snapshots opencode.diff.Snapshots
+local function show_diff(snapshots)
+  if not snapshots.first or not snapshots.last then
+    vim.notify("No snapshots found for session diff", vim.log.levels.WARN, { title = "opencode" })
+    return
+  end
+
+  if snapshots.first == snapshots.last then
+    vim.notify("No changes in session (same snapshot)", vim.log.levels.INFO, { title = "opencode" })
+    return
+  end
+
+  if not snapshots.project_id then
+    vim.notify("Could not determine project ID", vim.log.levels.ERROR, { title = "opencode" })
+    return
+  end
+
+  local snapshot_git = data_dir .. "/snapshot/" .. snapshots.project_id
+
+  -- Check if snapshot git directory exists
+  if vim.fn.isdirectory(snapshot_git) == 0 then
+    vim.notify("Snapshot directory not found: " .. snapshot_git, vim.log.levels.ERROR, { title = "opencode" })
+    return
+  end
+
+  -- Export both trees and show diff
+  export_tree(snapshot_git, snapshots.first, function(err1, dir1)
+    if err1 or not dir1 then
+      vim.notify(err1 or "Failed to export first snapshot", vim.log.levels.ERROR, { title = "opencode" })
+      return
+    end
+
+    export_tree(snapshot_git, snapshots.last, function(err2, dir2)
+      if err2 or not dir2 then
+        vim.notify(err2 or "Failed to export second snapshot", vim.log.levels.ERROR, { title = "opencode" })
+        return
+      end
+
+      -- Show diff using codediff.nvim
+      vim.notify(
+        "Session diff: " .. snapshots.first:sub(1, 7) .. " → " .. snapshots.last:sub(1, 7),
+        vim.log.levels.INFO,
+        { title = "opencode" }
+      )
+
+      -- Use CodeDiff command to compare directories
+      local ok, cmd_err = pcall(function()
+        vim.cmd("CodeDiff " .. vim.fn.fnameescape(dir1) .. " " .. vim.fn.fnameescape(dir2))
+      end)
+      if not ok then
+        vim.notify("Failed to run CodeDiff: " .. tostring(cmd_err), vim.log.levels.ERROR, { title = "opencode" })
+      end
+    end)
+  end)
+end
+
+-- Show session-wide diff (first step-start → last step-finish across all messages)
+function M.session_diff()
+  local has_codediff = pcall(require, "codediff")
+  if not has_codediff then
+    vim.notify(
+      "codediff.nvim is required for session diff. Install it from https://github.com/esmuellert/codediff.nvim",
+      vim.log.levels.ERROR,
+      { title = "opencode" }
+    )
+    return
+  end
+
+  require("opencode.cli.server")
+    .get_port()
+    :next(function(port)
+      require("opencode.cli.client").get_sessions(port, function(sessions)
+        if not sessions or #sessions == 0 then
+          vim.notify("No sessions found", vim.log.levels.WARN, { title = "opencode" })
+          return
+        end
+
+        -- Sort by updated time, most recent first
+        table.sort(sessions, function(a, b)
+          local a_time = (a.time and a.time.updated) or 0
+          local b_time = (b.time and b.time.updated) or 0
+          return a_time > b_time
+        end)
+
+        vim.ui.select(sessions, {
+          prompt = "Select session to diff:",
+          format_item = function(session)
+            return string.format("%-20s", session.title or session.slug or session.id)
+          end,
+        }, function(choice)
+          if not choice then
+            return
+          end
+
+          local snapshots = find_session_snapshots(choice.id, choice.projectID)
+          show_diff(snapshots)
+        end)
+      end)
+    end)
+    :catch(function(err)
+      vim.notify(err, vim.log.levels.ERROR, { title = "opencode" })
+    end)
+end
+
+return M
diff --git a/lua/opencode/ui/select.lua b/lua/opencode/ui/select.lua
index 9e74829..a5724ad 100644
--- a/lua/opencode/ui/select.lua
+++ b/lua/opencode/ui/select.lua
@@ -16,6 +16,10 @@ local M = {}
 ---Or `false` to hide the commands section.
 ---@field commands? table<opencode.Command|string, string>|false
 ---
+---Whether to show the diff section.
+---Requires codediff.nvim to be installed.
+---@field diff? boolean
+---
 ---Whether to show the provider section.
 ---Always `false` if no provider is available.
 ---@field provider? boolean
@@ -140,6 +144,21 @@ function M.select(opts)
         end
       end
 
+      -- Diff section (requires codediff.nvim)
+      if opts.sections.diff then
+        local has_codediff = pcall(require, "codediff")
+        if has_codediff then
+          table.insert(items, { __group = true, name = "DIFF", preview = { text = "" } })
+          table.insert(items, {
+            __type = "diff",
+            name = "session diff",
+            text = "Pick a session to view diff of",
+            highlights = { { "Pick a session to view diff of", "Comment" } },
+            preview = { text = "" },
+          })
+        end
+      end
+
       -- Provider section
       if opts.sections.provider then
         table.insert(items, { __group = true, name = "PROVIDER", preview = { text = "" } })
@@ -230,6 +249,8 @@ function M.select(opts)
           elseif choice.name == "stop" then
             require("opencode").stop()
           end
+        elseif choice.__type == "diff" then
+          require("opencode.diff").session_diff()
         end
       end)
     end)