diff --git a/lua/codecompanion/config.lua b/lua/codecompanion/config.lua
index 37ad7798e..24e89df56 100644
--- a/lua/codecompanion/config.lua
+++ b/lua/codecompanion/config.lua
@@ -517,6 +517,21 @@ If you are providing code changes, use the insert_edit_into_file tool (if availa
             interactions = { "chat", "cli" },
           },
         },
+        ["save"] = {
+          path = "interactions.chat.slash_commands.builtin.save",
+          description = "Save the chat as a persistent session",
+          ---@param opts { adapter: CodeCompanion.HTTPAdapter|CodeCompanion.ACPAdapter }
+          ---@return boolean
+          enabled = function(opts)
+            if opts.adapter and opts.adapter.type == "http" then
+              return true
+            end
+            return false
+          end,
+          opts = {
+            contains_code = false,
+          },
+        },
         ["share"] = {
           path = "interactions.chat.slash_commands.builtin.share",
           description = "Share the chat in a GitHub Gist",
diff --git a/lua/codecompanion/interactions/chat/init.lua b/lua/codecompanion/interactions/chat/init.lua
index 5dd577128..6d3e3b2e9 100644
--- a/lua/codecompanion/interactions/chat/init.lua
+++ b/lua/codecompanion/interactions/chat/init.lua
@@ -1931,6 +1931,56 @@ function Chat:clear()
   utils.fire("ChatCleared", { bufnr = self.bufnr, id = self.id })
 end
 
+---Creates a serializable snapshot of the chat for use in saving sessions to disk
+---@return table
+function Chat:snapshot()
+  local snapshot_messages = {}
+  for _, msg in ipairs(self.messages or {}) do
+    local entry = {
+      role = msg.role,
+      content = msg.content,
+    }
+    if msg.reasoning ~= nil then
+      entry.reasoning = vim.deepcopy(msg.reasoning)
+    end
+    if msg.tools ~= nil then
+      entry.tools = vim.deepcopy(msg.tools)
+    end
+    if msg.opts ~= nil then
+      entry.opts = { visible = msg.opts.visible }
+    end
+    if msg.context ~= nil then
+      entry.context = vim.deepcopy(msg.context)
+    end
+    if msg._meta and msg._meta.tag ~= nil then
+      entry._meta = { tag = msg._meta.tag }
+    end
+    table.insert(snapshot_messages, entry)
+  end
+
+  local adapter = {
+    name = self.adapter and self.adapter.name,
+    type = self.adapter and self.adapter.type,
+  }
+  if self.adapter and self.adapter.schema and self.adapter.schema.model then
+    adapter.model = self.adapter.schema.model.default
+  end
+
+  local winid = vim.fn.bufwinid(self.bufnr)
+  local cwd = winid ~= -1 and vim.fn.getcwd(winid) or vim.fn.getcwd()
+
+  return {
+    adapter = adapter,
+    context_items = vim.deepcopy(self.context_items or {}),
+    cwd = cwd,
+    cycle = self.cycle,
+    id = self.id,
+    messages = snapshot_messages,
+    settings = self.settings and vim.deepcopy(self.settings) or nil,
+    title = self.title,
+  }
+end
+
 ---Display the chat buffer's settings and messages
 function Chat:debug()
   if vim.tbl_isempty(self.messages) then
diff --git a/lua/codecompanion/interactions/chat/sessions/init.lua b/lua/codecompanion/interactions/chat/sessions/init.lua
new file mode 100644
index 000000000..5e27c0bba
--- /dev/null
+++ b/lua/codecompanion/interactions/chat/sessions/init.lua
@@ -0,0 +1,179 @@
+---Persistent chat sessions.
+---
+---Lives outside the Chat class; interacts with it through:
+---  - `chat:snapshot()` for state reads (the only supported read seam)
+---  - `chat:add_callback()` for `on_completed` / `on_closed` lifecycle hooks
+---  - `Chat.new()` for restoration
+---
+---Chat has no knowledge of sessions. Tracking state (which chat is being
+---auto-saved under which slug) lives here, keyed by chat id.
+
+local log = require("codecompanion.utils.log")
+local serializer = require("codecompanion.interactions.chat.sessions.serializer")
+local slug_utils = require("codecompanion.interactions.chat.sessions.slug")
+local storage = require("codecompanion.interactions.chat.sessions.storage")
+local utils = require("codecompanion.utils")
+
+local api = vim.api
+
+local M = {}
+
+---Per-chat tracking. Indexed by `chat.id`.
+---@type table<number, { slug: string, created_at: string, autosave: boolean }>
+local sessions = {}
+
+---@return string
+local function now_iso()
+  return os.date("!%Y-%m-%dT%H:%M:%SZ") --[[@as string]]
+end
+
+---@param chat CodeCompanion.Chat
+---@param title string
+---@return string slug
+local function resolve_slug(chat, title)
+  local base = slug_utils.slugify(title)
+  local current = sessions[chat.id] and sessions[chat.id].slug
+  return slug_utils.disambiguate(base, storage.exists, current)
+end
+
+---Write the current state of a tracked chat to disk.
+---@param chat CodeCompanion.Chat
+---@return boolean ok
+local function write_session(chat)
+  local entry = sessions[chat.id]
+  if not entry then
+    return false
+  end
+
+  local snapshot = chat:snapshot()
+  local data = serializer.encode(snapshot, {
+    slug = entry.slug,
+    created_at = entry.created_at,
+    updated_at = now_iso(),
+  })
+
+  local ui_lines = api.nvim_buf_is_valid(chat.bufnr) and api.nvim_buf_get_lines(chat.bufnr, 0, -1, false) or nil
+
+  local ok = storage.write(entry.slug, data, ui_lines)
+  if ok then
+    log:debug("[sessions] Wrote session %s for chat %d", entry.slug, chat.id)
+  end
+  return ok
+end
+
+---Attach the auto-save callbacks to a chat.
+---@param chat CodeCompanion.Chat
+local function attach_autosave(chat)
+  chat:add_callback("on_completed", function(c)
+    if sessions[c.id] and sessions[c.id].autosave then
+      write_session(c)
+    end
+  end)
+  chat:add_callback("on_closed", function(c)
+    if sessions[c.id] and sessions[c.id].autosave then
+      write_session(c)
+      sessions[c.id] = nil
+    end
+  end)
+end
+
+---Save the chat as a session. On first call, prompts for a title if the chat
+---has none; subsequent calls just write to disk.
+---@param chat CodeCompanion.Chat
+---@param opts? { title?: string }
+---@return nil
+function M.save(chat, opts)
+  opts = opts or {}
+
+  if chat.adapter and chat.adapter.type ~= "http" then
+    return utils.notify("Sessions only support HTTP chats", vim.log.levels.WARN)
+  end
+
+  -- Existing tracked session: just rewrite under the current slug.
+  if sessions[chat.id] then
+    if opts.title and opts.title ~= "" and opts.title ~= chat.title then
+      M._rename(chat, opts.title)
+    end
+    if write_session(chat) then
+      utils.notify("Session saved: " .. sessions[chat.id].slug)
+    end
+    return
+  end
+
+  local function persist_with_title(title)
+    if not title or title == "" then
+      return
+    end
+    if chat.title ~= title then
+      chat:set_title(title)
+    end
+
+    local slug = resolve_slug(chat, title)
+    sessions[chat.id] = {
+      autosave = true,
+      created_at = now_iso(),
+      slug = slug,
+    }
+    attach_autosave(chat)
+
+    if write_session(chat) then
+      utils.notify("Session saved: " .. slug)
+      utils.fire("ChatSessionSaved", { bufnr = chat.bufnr, id = chat.id, slug = slug })
+    end
+  end
+
+  local prefill = opts.title or chat.title
+  if prefill and prefill ~= "" then
+    return persist_with_title(prefill)
+  end
+
+  vim.ui.input({ prompt = " Session Title " }, function(input)
+    if input == nil then
+      return
+    end
+    persist_with_title(input)
+  end)
+end
+
+---Rename a tracked session by moving its files on disk.
+---@param chat CodeCompanion.Chat
+---@param new_title string
+---@return nil
+function M._rename(chat, new_title)
+  local entry = sessions[chat.id]
+  if not entry then
+    return
+  end
+
+  local new_slug = resolve_slug(chat, new_title)
+  if new_slug == entry.slug then
+    chat:set_title(new_title)
+    return
+  end
+
+  -- Delete old files; the next write under new_slug creates fresh ones.
+  storage.delete(entry.slug)
+  entry.slug = new_slug
+  chat:set_title(new_title)
+end
+
+---Disable auto-save for a chat (e.g. after `/fork` produces a new chat).
+---@param chat_id number
+function M.untrack(chat_id)
+  sessions[chat_id] = nil
+end
+
+---Whether a chat is currently being tracked for auto-save.
+---@param chat_id number
+---@return boolean
+function M.is_tracked(chat_id)
+  return sessions[chat_id] ~= nil
+end
+
+---@param chat_id number
+---@return { slug: string, created_at: string, autosave: boolean }|nil
+function M.get(chat_id)
+  return sessions[chat_id]
+end
+
+return M
diff --git a/lua/codecompanion/interactions/chat/sessions/serializer.lua b/lua/codecompanion/interactions/chat/sessions/serializer.lua
new file mode 100644
index 000000000..a56d42dd4
--- /dev/null
+++ b/lua/codecompanion/interactions/chat/sessions/serializer.lua
@@ -0,0 +1,68 @@
+---Convert a Chat snapshot to and from the on-disk JSON form.
+---
+---The schema version is pinned here. Bump `SCHEMA_VERSION` when the on-disk
+---shape changes incompatibly, and add a migrator.
+
+local M = {}
+
+M.SCHEMA_VERSION = 1
+M.UI_VERSION = 1
+
+---Build the JSON-serializable table for a session.
+---@param snapshot table A Chat snapshot (see Chat:snapshot)
+---@param extra { slug: string, created_at?: string, updated_at: string }
+---@return table
+function M.encode(snapshot, extra)
+  return {
+    adapter = snapshot.adapter,
+    context_items = snapshot.context_items,
+    created_at = extra.created_at or extra.updated_at,
+    cwd = snapshot.cwd,
+    cycle = snapshot.cycle,
+    id = snapshot.id,
+    messages = snapshot.messages,
+    schema_version = M.SCHEMA_VERSION,
+    settings = snapshot.settings,
+    slug = extra.slug,
+    title = snapshot.title,
+    ui_version = M.UI_VERSION,
+    updated_at = extra.updated_at,
+  }
+end
+
+---Convert a decoded JSON table into args usable by `Chat.new`.
+---Runtime-only message fields (cycle, id, estimated_tokens, sent, index) are
+---left for the chat constructor / backfill to recompute.
+---@param data table The decoded JSON
+---@return table args Suitable for passing to `Chat.new`
+function M.to_chat_args(data)
+  local messages = {}
+  for _, msg in ipairs(data.messages or {}) do
+    local entry = {
+      role = msg.role,
+      content = msg.content,
+      reasoning = msg.reasoning,
+    }
+    if msg.tools then
+      entry.tools = msg.tools
+    end
+    if msg.opts then
+      entry.opts = { visible = msg.opts.visible }
+    end
+    if msg.context then
+      entry.context = msg.context
+    end
+    if msg._meta then
+      entry._meta = { tag = msg._meta.tag }
+    end
+    table.insert(messages, entry)
+  end
+
+  return {
+    messages = messages,
+    settings = data.settings,
+    title = data.title,
+  }
+end
+
+return M
diff --git a/lua/codecompanion/interactions/chat/sessions/slug.lua b/lua/codecompanion/interactions/chat/sessions/slug.lua
new file mode 100644
index 000000000..54a8f4fe7
--- /dev/null
+++ b/lua/codecompanion/interactions/chat/sessions/slug.lua
@@ -0,0 +1,47 @@
+---Slugify and disambiguate session titles for use as filenames.
+
+local M = {}
+
+---Convert a title into a filesystem-safe slug.
+---Lowercase, ASCII alphanumerics + hyphens, collapsed and trimmed.
+---@param title string
+---@return string
+function M.slugify(title)
+  if type(title) ~= "string" or title == "" then
+    return "untitled"
+  end
+
+  local slug = title:lower()
+  slug = slug:gsub("[^%w%s%-_]", "")
+  slug = slug:gsub("[%s_]+", "-")
+  slug = slug:gsub("%-+", "-")
+  slug = slug:gsub("^%-+", ""):gsub("%-+$", "")
+
+  if slug == "" then
+    return "untitled"
+  end
+  return slug
+end
+
+---Resolve a slug against an existing-slug check, appending `-2`, `-3` etc. on collision.
+---The current slug (if any) is exempt — a session re-saving under its own slug keeps it.
+---@param base string Base slug from slugify()
+---@param exists fun(slug: string): boolean Predicate: is this slug taken on disk?
+---@param current_slug? string The session's own existing slug (treated as available)
+---@return string
+function M.disambiguate(base, exists, current_slug)
+  if base == current_slug or not exists(base) then
+    return base
+  end
+
+  local n = 2
+  while true do
+    local candidate = base .. "-" .. n
+    if candidate == current_slug or not exists(candidate) then
+      return candidate
+    end
+    n = n + 1
+  end
+end
+
+return M
diff --git a/lua/codecompanion/interactions/chat/sessions/storage.lua b/lua/codecompanion/interactions/chat/sessions/storage.lua
new file mode 100644
index 000000000..a98549402
--- /dev/null
+++ b/lua/codecompanion/interactions/chat/sessions/storage.lua
@@ -0,0 +1,137 @@
+---Read and write session files to disk.
+---
+---Layout under the session directory:
+---  {slug}_chat.json  — schema-versioned session state
+---  {slug}_ui.md      — rendered chat buffer markdown
+
+local log = require("codecompanion.utils.log")
+
+local M = {}
+
+local DEFAULT_DIR = vim.fn.stdpath("data") .. "/codecompanion/sessions"
+
+---Override the storage directory (used by tests).
+---@type string|nil
+local override_dir = nil
+
+---@return string
+function M.dir()
+  return override_dir or DEFAULT_DIR
+end
+
+---@param path string|nil
+function M.set_dir(path)
+  override_dir = path
+end
+
+---@return nil
+function M.ensure_dir()
+  vim.fn.mkdir(M.dir(), "p")
+end
+
+---@param slug string
+---@return string
+function M.json_path(slug)
+  return M.dir() .. "/" .. slug .. "_chat.json"
+end
+
+---@param slug string
+---@return string
+function M.ui_path(slug)
+  return M.dir() .. "/" .. slug .. "_ui.md"
+end
+
+---@param slug string
+---@return boolean
+function M.exists(slug)
+  return vim.fn.filereadable(M.json_path(slug)) == 1
+end
+
+---@param path string
+---@param contents string
+---@return boolean ok
+local function write_file(path, contents)
+  local fd, err = io.open(path, "w")
+  if not fd then
+    log:error("[sessions::storage] Could not open %s for write: %s", path, err or "unknown")
+    return false
+  end
+  fd:write(contents)
+  fd:close()
+  return true
+end
+
+---@param path string
+---@return string|nil
+local function read_file(path)
+  local fd, err = io.open(path, "r")
+  if not fd then
+    log:debug("[sessions::storage] Could not read %s: %s", path, err or "unknown")
+    return nil
+  end
+  local contents = fd:read("*a")
+  fd:close()
+  return contents
+end
+
+---@param slug string
+---@param data table The encoded JSON-shaped table
+---@param ui_lines string[] The rendered chat buffer lines
+---@return boolean ok
+function M.write(slug, data, ui_lines)
+  M.ensure_dir()
+  local ok, encoded = pcall(vim.json.encode, data)
+  if not ok then
+    log:error("[sessions::storage] Failed to encode session %s: %s", slug, encoded)
+    return false
+  end
+  if not write_file(M.json_path(slug), encoded) then
+    return false
+  end
+  if ui_lines and not write_file(M.ui_path(slug), table.concat(ui_lines, "\n")) then
+    return false
+  end
+  return true
+end
+
+---@param slug string
+---@return table|nil data, string[]|nil ui_lines
+function M.read(slug)
+  local raw = read_file(M.json_path(slug))
+  if not raw then
+    return nil, nil
+  end
+  local ok, data = pcall(vim.json.decode, raw)
+  if not ok then
+    log:error("[sessions::storage] Failed to decode session %s: %s", slug, data)
+    return nil, nil
+  end
+
+  local ui_raw = read_file(M.ui_path(slug))
+  local ui_lines = ui_raw and vim.split(ui_raw, "\n", { plain = true }) or nil
+  return data, ui_lines
+end
+
+---@param slug string
+---@return boolean ok
+function M.delete(slug)
+  local ok_json = pcall(os.remove, M.json_path(slug))
+  pcall(os.remove, M.ui_path(slug))
+  return ok_json
+end
+
+---List all session slugs on disk.
+---@return string[]
+function M.list_slugs()
+  local pattern = M.dir() .. "/*_chat.json"
+  local files = vim.fn.glob(pattern, true, true)
+  local slugs = {}
+  for _, file in ipairs(files) do
+    local name = vim.fn.fnamemodify(file, ":t:r") -- strip dir + extension
+    local slug = name:gsub("_chat$", "")
+    table.insert(slugs, slug)
+  end
+  return slugs
+end
+
+return M
diff --git a/lua/codecompanion/interactions/chat/slash_commands/builtin/save.lua b/lua/codecompanion/interactions/chat/slash_commands/builtin/save.lua
new file mode 100644
index 000000000..66460998b
--- /dev/null
+++ b/lua/codecompanion/interactions/chat/slash_commands/builtin/save.lua
@@ -0,0 +1,33 @@
+local sessions = require("codecompanion.interactions.chat.sessions")
+local utils = require("codecompanion.utils")
+
+---@class CodeCompanion.SlashCommand.Save: CodeCompanion.SlashCommand
+local SlashCommand = {}
+
+---@param args CodeCompanion.SlashCommandArgs
+function SlashCommand.new(args)
+  return setmetatable({
+    Chat = args.Chat,
+    config = args.config,
+    context = args.context,
+  }, { __index = SlashCommand })
+end
+
+---@param chat CodeCompanion.Chat
+---@return boolean, string
+function SlashCommand.enabled(chat)
+  if not chat.adapter or chat.adapter.type ~= "http" then
+    return false, "The /save command only supports HTTP chats"
+  end
+  return true, ""
+end
+
+---@return nil
+function SlashCommand:execute()
+  if vim.tbl_isempty(self.Chat.messages or {}) then
+    return utils.notify("Nothing to save — chat is empty", vim.log.levels.WARN)
+  end
+  sessions.save(self.Chat)
+end
+
+return SlashCommand