diff --git a/lua/opencode/event_manager.lua b/lua/opencode/event_manager.lua
index 7eeeb4c5..f42777d8 100644
--- a/lua/opencode/event_manager.lua
+++ b/lua/opencode/event_manager.lua
@@ -23,6 +23,16 @@ local util = require('opencode.util')
 --- @field type "message.part.updated"
 --- @field properties {part: OpencodeMessagePart}
 
+--- @class EventMessagePartDelta
+--- @field type "message.part.delta"
+--- @field properties {
+---   sessionID: string,
+---   messageID: string,
+---   partID: string,
+---   field: string,
+---   delta: string
+--- }
+
 --- @class EventMessagePartRemoved
 --- @field type "message.part.removed"
 --- @field properties {sessionID: string, messageID: string, partID: string}
@@ -128,6 +138,7 @@ local util = require('opencode.util')
 --- | "message.updated"
 --- | "message.removed"
 --- | "message.part.updated"
+--- | "message.part.delta"
 --- | "message.part.removed"
 --- | "session.compacted"
 --- | "session.idle"
@@ -170,6 +181,7 @@ function EventManager.new()
     state_server_listener = nil,
     is_started = false,
     captured_events = {},
+    _parts_by_id = {},
   }, EventManager)
 
   local throttle_ms = config.ui.output.rendering.event_throttle_ms
@@ -186,6 +198,7 @@ end
 --- @overload fun(self: EventManager, event_name: "message.updated", callback: fun(data: EventMessageUpdated['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "message.removed", callback: fun(data: EventMessageRemoved['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "message.part.updated", callback: fun(data: EventMessagePartUpdated['properties']): nil)
+--- @overload fun(self: EventManager, event_name: "message.part.delta", callback: fun(data: EventMessagePartDelta['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "message.part.removed", callback: fun(data: EventMessagePartRemoved['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "session.compacted", callback: fun(data: EventSessionCompacted['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "session.idle", callback: fun(data: EventSessionIdle['properties']): nil)
@@ -226,6 +239,7 @@ end
 --- @overload fun(self: EventManager, event_name: "message.updated", callback: fun(data: EventMessageUpdated['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "message.removed", callback: fun(data: EventMessageRemoved['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "message.part.updated", callback: fun(data: EventMessagePartUpdated['properties']): nil)
+--- @overload fun(self: EventManager, event_name: "message.part.delta", callback: fun(data: EventMessagePartDelta['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "message.part.removed", callback: fun(data: EventMessagePartRemoved['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "session.compacted", callback: fun(data: EventSessionCompacted['properties']): nil)
 --- @overload fun(self: EventManager, event_name: "session.idle", callback: fun(data: EventSessionIdle['properties']): nil)
@@ -260,6 +274,76 @@ function EventManager:unsubscribe(event_name, callback)
   end
 end
 
+---Normalize message.part.delta events into message.part.updated events so
+---consumers can continue rendering full part payloads.
+---@param event table
+---@return table|nil
+function EventManager:_normalize_stream_event(event)
+  if not event or not event.type then
+    return nil
+  end
+
+  local properties = event.properties or {}
+
+  if event.type == 'message.part.updated' and properties.part and properties.part.id then
+    self._parts_by_id[properties.part.id] = vim.deepcopy(properties.part)
+    return event
+  end
+
+  if event.type == 'message.part.removed' and properties.partID then
+    self._parts_by_id[properties.partID] = nil
+    return event
+  end
+
+  if event.type ~= 'message.part.delta' then
+    return event
+  end
+
+  local part_id = properties.partID
+  local message_id = properties.messageID
+  local session_id = properties.sessionID
+  local field = properties.field
+
+  if not part_id or not message_id or not session_id or not field then
+    return nil
+  end
+
+  local part = vim.deepcopy(self._parts_by_id[part_id])
+  if not part then
+    part = {
+      id = part_id,
+      messageID = message_id,
+      sessionID = session_id,
+    }
+
+    if field == 'text' then
+      part.type = 'text'
+      part.text = ''
+    end
+  end
+
+  local delta = properties.delta
+  local current = part[field]
+  if type(delta) == 'string' then
+    if type(current) == 'string' then
+      part[field] = current .. delta
+    else
+      part[field] = delta
+    end
+  else
+    part[field] = delta
+  end
+
+  self._parts_by_id[part_id] = part
+
+  return {
+    type = 'message.part.updated',
+    properties = {
+      part = part,
+    },
+  }
+end
+
 ---Callback from ThrottlingEmitter when the events are now ready to be processed.
 ---Collapses parts that are duplicated, making sure to replace earlier parts with later
 ---ones (but keeping the earlier position)
@@ -267,8 +351,16 @@ end
 function EventManager:_on_drained_events(events)
   self:emit('custom.emit_events.started', {})
 
+  local normalized_events = {}
+  for _, event in ipairs(events) do
+    local normalized_event = self:_normalize_stream_event(event)
+    if normalized_event then
+      table.insert(normalized_events, normalized_event)
+    end
+  end
+
   if not config.ui.output.rendering.event_collapsing then
-    for _, event in ipairs(events) do
+    for _, event in ipairs(normalized_events) do
       self:emit(event.type, event.properties)
     end
     self:emit('custom.emit_events.finished', {})
@@ -278,7 +370,7 @@ function EventManager:_on_drained_events(events)
   local collapsed_events = {}
   local part_update_indices = {}
 
-  for i, event in ipairs(events) do
+  for i, event in ipairs(normalized_events) do
     if event.type == 'message.part.updated' and event.properties.part then
       local part_id = event.properties.part.id
       if part_update_indices[part_id] then
@@ -289,7 +381,10 @@ function EventManager:_on_drained_events(events)
         -- permission.updated/permission.asked sits between the two updates.
         local has_intervening_permission_event = false
         for j = previous_index + 1, i - 1 do
-          if events[j] and (events[j].type == 'permission.updated' or events[j].type == 'permission.asked') then
+          if normalized_events[j] and (
+            normalized_events[j].type == 'permission.updated'
+            or normalized_events[j].type == 'permission.asked'
+          ) then
             has_intervening_permission_event = true
             break
           end
@@ -312,7 +407,7 @@ function EventManager:_on_drained_events(events)
     end
   end
 
-  for i = 1, #events do
+  for i = 1, #normalized_events do
     local event = collapsed_events[i]
     if event then
       self:emit(event.type, event.properties)
@@ -404,6 +499,7 @@ function EventManager:stop()
   self:_cleanup_server_subscription()
 
   self.throttling_emitter:clear()
+  self._parts_by_id = {}
   self.events = {}
 end
 
diff --git a/tests/helpers.lua b/tests/helpers.lua
index 189741b9..53d15189 100644
--- a/tests/helpers.lua
+++ b/tests/helpers.lua
@@ -174,6 +174,7 @@ end
 
 function M.load_session_from_events(events)
   local session_data = {}
+  local parts_by_id = {}
 
   for _, event in ipairs(events) do
     local properties = event.properties
@@ -210,12 +211,53 @@ function M.load_session_from_events(events)
 
           if existing_part then
             msg.parts[existing_part] = vim.deepcopy(part)
+            parts_by_id[part.id] = msg.parts[existing_part]
           else
             table.insert(msg.parts, vim.deepcopy(part))
+            parts_by_id[part.id] = msg.parts[#msg.parts]
           end
           break
         end
       end
+    elseif event.type == 'message.part.delta'
+      and properties.partID
+      and properties.messageID
+      and properties.field then
+      local part = parts_by_id[properties.partID]
+
+      if not part then
+        for _, msg in ipairs(session_data) do
+          if msg.info.id == properties.messageID then
+            part = {
+              id = properties.partID,
+              messageID = properties.messageID,
+              sessionID = properties.sessionID,
+              type = properties.field == 'text' and 'text' or nil,
+            }
+            if properties.field == 'text' then
+              part.text = ''
+            end
+            table.insert(msg.parts, part)
+            parts_by_id[properties.partID] = part
+            break
+          end
+        end
+      end
+
+      if part then
+        local field = properties.field
+        local delta = properties.delta
+        if type(delta) == 'string' then
+          local current = part[field]
+          if type(current) == 'string' then
+            part[field] = current .. delta
+          else
+            part[field] = delta
+          end
+        else
+          part[field] = delta
+        end
+      end
     end
   end
 
@@ -247,7 +289,9 @@ function M.get_session_from_events(events, with_session_updates)
   for _, event in ipairs(events) do
     -- find the session id in a message or part event
     local properties = event.properties
-    local session_id = properties.info and properties.info.sessionID or properties.part and properties.part.sessionID
+    local session_id = properties.info and properties.info.sessionID
+      or properties.part and properties.part.sessionID
+      or properties.sessionID
 
     if session_id then
       ---@diagnostic disable-next-line: missing-fields
diff --git a/tests/unit/event_manager_spec.lua b/tests/unit/event_manager_spec.lua
index 01915f87..3eb79074 100644
--- a/tests/unit/event_manager_spec.lua
+++ b/tests/unit/event_manager_spec.lua
@@ -1,6 +1,7 @@
 local EventManager = require('opencode.event_manager')
 local Promise = require('opencode.promise')
 local state = require('opencode.state')
+local config = require('opencode.config')
 
 describe('EventManager', function()
   local event_manager
@@ -189,6 +190,93 @@ describe('EventManager', function()
     vim.defer_fn = original_defer_fn
   end)
 
+  it('normalizes message.part.delta into message.part.updated', function()
+    local original_event_collapsing = config.ui.output.rendering.event_collapsing
+    config.ui.output.rendering.event_collapsing = true
+
+    local received = {}
+    event_manager:subscribe('message.part.updated', function(data)
+      table.insert(received, vim.deepcopy(data.part))
+    end)
+
+    event_manager:_on_drained_events({
+      {
+        type = 'message.part.updated',
+        properties = {
+          part = {
+            id = 'part_1',
+            messageID = 'msg_1',
+            sessionID = 'ses_1',
+            type = 'text',
+            text = '',
+          },
+        },
+      },
+      {
+        type = 'message.part.delta',
+        properties = {
+          partID = 'part_1',
+          messageID = 'msg_1',
+          sessionID = 'ses_1',
+          field = 'text',
+          delta = 'hello',
+        },
+      },
+      {
+        type = 'message.part.delta',
+        properties = {
+          partID = 'part_1',
+          messageID = 'msg_1',
+          sessionID = 'ses_1',
+          field = 'text',
+          delta = ' world',
+        },
+      },
+    })
+
+    config.ui.output.rendering.event_collapsing = original_event_collapsing
+
+    assert.are.equal(1, #received)
+    assert.are.equal('hello world', received[1].text)
+  end)
+
+  it('keeps accumulated delta text across event batches', function()
+    local received = {}
+    event_manager:subscribe('message.part.updated', function(data)
+      table.insert(received, vim.deepcopy(data.part))
+    end)
+
+    event_manager:_on_drained_events({
+      {
+        type = 'message.part.updated',
+        properties = {
+          part = {
+            id = 'part_2',
+            messageID = 'msg_2',
+            sessionID = 'ses_2',
+            type = 'text',
+            text = '',
+          },
+        },
+      },
+    })
+
+    event_manager:_on_drained_events({
+      {
+        type = 'message.part.delta',
+        properties = {
+          partID = 'part_2',
+          messageID = 'msg_2',
+          sessionID = 'ses_2',
+          field = 'text',
+          delta = 'abc',
+        },
+      },
+    })
+
+    assert.are.equal('abc', received[#received].text)
+  end)
+
   describe('User autocmd events', function()
     it('should fire User autocmd when emitting events', function()
       local autocmd_called = false