diff --git a/lua/opencode/config.lua b/lua/opencode/config.lua
index 315344a9..923c84b4 100644
--- a/lua/opencode/config.lua
+++ b/lua/opencode/config.lua
@@ -160,6 +160,7 @@ M.defaults = {
     },
     output = {
       filetype = 'opencode_output',
+      time_format = nil,
       compact_assistant_headers = false,
       rendering = {
         markdown_debounce_ms = 250,
diff --git a/lua/opencode/types.lua b/lua/opencode/types.lua
index c418b199..4b83a9d4 100644
--- a/lua/opencode/types.lua
+++ b/lua/opencode/types.lua
@@ -253,6 +253,7 @@
 ---@field event_collapsing boolean
 
 ---@class OpencodeUIOutputConfig
+---@field time_format string|nil # Custom os.date format for timestamps, e.g. '%m/%d %H:%M'. Uses fixed default when nil.
 ---@field tools { show_output: boolean, show_reasoning_output: boolean, use_folds: boolean, folding_threshold: number }
 ---@field rendering OpencodeUIOutputRenderingConfig
 ---@field max_messages integer|nil
diff --git a/lua/opencode/util.lua b/lua/opencode/util.lua
index 1f51a76f..f414ea01 100644
--- a/lua/opencode/util.lua
+++ b/lua/opencode/util.lua
@@ -224,11 +224,19 @@ function M.format_time(timestamp)
     return ''
   end
 
+  local config = require('opencode.config')
+  local time_format = config.ui.output.time_format
+
+  if time_format then
+    return os.date(time_format, timestamp)
+  end
+
+  local saved = os.setlocale('C', 'time')
   local same_day = os.date('%Y-%m-%d') == os.date('%Y-%m-%d', timestamp)
   local same_year = os.date('%Y') == os.date('%Y', timestamp)
   local locale_time = vim.trim(os.date('%X', timestamp) or '')
+  os.setlocale(saved, 'time')
 
-  -- Keep output close to previous formatting by dropping seconds when present.
   locale_time = locale_time:gsub('^(%d?%d:%d%d):%d%d(.*)$', '%1%2')
   if locale_time == '' then
     locale_time = vim.trim(os.date('%H:%M', timestamp) or '')
@@ -238,11 +246,16 @@ function M.format_time(timestamp)
     return locale_time
   end
 
+  saved = os.setlocale('C', 'time')
+  local date_part
   if same_year then
-    return string.format('%s %s', os.date('%d %b', timestamp), locale_time)
+    date_part = os.date('%d %b', timestamp)
+  else
+    date_part = os.date('%d %b %Y', timestamp)
   end
+  os.setlocale(saved, 'time')
 
-  return string.format('%s %s', os.date('%d %b %Y', timestamp), locale_time)
+  return string.format('%s %s', date_part, locale_time)
 end
 
 ---@param timestamp number
diff --git a/tests/unit/util_spec.lua b/tests/unit/util_spec.lua
index 778b5aa8..958ece76 100644
--- a/tests/unit/util_spec.lua
+++ b/tests/unit/util_spec.lua
@@ -103,8 +103,17 @@ describe('util.format_time', function()
     return os.time({ year = year, month = month, day = day, hour = hour or 0, min = min or 0, sec = sec or 0 })
   end
 
+  local function c_locale_date(fmt, timestamp)
+    local saved = os.setlocale('C', 'time')
+    local result = os.date(fmt, timestamp)
+    os.setlocale(saved, 'time')
+    return result
+  end
+
   local function compact_locale_time(timestamp)
+    local saved = os.setlocale('C', 'time')
     local locale_time = vim.trim(os.date('%X', timestamp) or '')
+    os.setlocale(saved, 'time')
     locale_time = locale_time:gsub('^(%d?%d:%d%d):%d%d(.*)$', '%1%2')
     if locale_time == '' then
       locale_time = vim.trim(os.date('%H:%M', timestamp) or '')
@@ -152,21 +161,21 @@ describe('util.format_time', function()
   describe('other day timestamps', function()
     it('formats yesterday with date prefix and locale time', function()
       local result = util.format_time(yesterday)
-      local expected_prefix = os.date('%d %b', yesterday) .. ' '
+      local expected_prefix = c_locale_date('%d %b', yesterday) .. ' '
       assert.is_true(vim.startswith(result, expected_prefix))
       assert.equals(compact_locale_time(yesterday), result:sub(#expected_prefix + 1))
     end)
 
     it('formats last week with date prefix and locale time', function()
       local result = util.format_time(last_week)
-      local expected_prefix = os.date('%d %b', last_week) .. ' '
+      local expected_prefix = c_locale_date('%d %b', last_week) .. ' '
       assert.is_true(vim.startswith(result, expected_prefix))
       assert.equals(compact_locale_time(last_week), result:sub(#expected_prefix + 1))
     end)
 
     it('formats future date with full date and locale time', function()
       local result = util.format_time(next_year)
-      local expected_prefix = os.date('%d %b %Y', next_year) .. ' '
+      local expected_prefix = c_locale_date('%d %b %Y', next_year) .. ' '
       assert.is_true(vim.startswith(result, expected_prefix))
       assert.equals(compact_locale_time(next_year), result:sub(#expected_prefix + 1))
       assert.matches('%d%d%d%d', result)
@@ -230,7 +239,7 @@ describe('util.format_time', function()
       if os.date('%Y-%m-%d', early_tomorrow) == os.date('%Y-%m-%d') then
         assert.equals(compact_locale_time(early_tomorrow), early_result)
       else
-        local expected_prefix = os.date('%d %b', early_tomorrow) .. ' '
+        local expected_prefix = c_locale_date('%d %b', early_tomorrow) .. ' '
         assert.is_true(vim.startswith(early_result, expected_prefix))
         assert.equals(compact_locale_time(early_tomorrow), early_result:sub(#expected_prefix + 1))
       end