diff --git a/cylc/flow/job_runner_mgr.py b/cylc/flow/job_runner_mgr.py
index 6aa6403c98..088a52fdaf 100644
--- a/cylc/flow/job_runner_mgr.py
+++ b/cylc/flow/job_runner_mgr.py
@@ -24,6 +24,10 @@
 """
 
 from contextlib import suppress
+from dataclasses import (
+    asdict,
+    dataclass,
+)
 import json
 import os
 from pathlib import Path
@@ -34,10 +38,12 @@
 from subprocess import DEVNULL  # nosec
 import sys
 import traceback
-from typing import Optional
+from typing import (
+    List,
+    Optional,
+)
 
 from cylc.flow.cylc_subproc import procopen
-from cylc.flow.parsec.OrderedDict import OrderedDict
 from cylc.flow.task_job_logs import (
     JOB_LOG_ERR,
     JOB_LOG_JOB,
@@ -55,59 +61,36 @@
 from cylc.flow.wallclock import get_current_time_string
 
 
-class JobPollContext():
+@dataclass
+class JobPollContext:
     """Context object for a job poll."""
-    CONTEXT_ATTRIBUTES = (
-        'job_log_dir',  # cycle/task/submit_num
-        'job_runner_name',
-        'job_id',  # job id in job runner
-        'job_runner_exit_polled',  # 0 for false, 1 for true
-        'run_status',  # 0 for success, 1 for failure
-        'run_signal',  # signal received on run failure
-        'time_submit_exit',  # submit (exit) time
-        'time_run',  # run start time
-        'time_run_exit',  # run exit time
-        'job_runner_call_no_lines',  # line count in job runner call stdout
-    )
-
-    __slots__ = CONTEXT_ATTRIBUTES + (
-        'pid',
-        'messages'
-    )
-
-    def __init__(self, job_log_dir, **attrs):
-        self.job_log_dir = job_log_dir
-        self.job_runner_name: Optional[str] = None
-        self.job_id = None
-        self.job_runner_exit_polled: Optional[int] = None
+    job_log_dir: str  # cycle/task/submit_num
+    job_runner_name: Optional[str] = None
+    job_id = None  # job id in job runner
+    job_runner_exit_polled: Optional[int] = None  # 0 for false, 1 for true
+    run_status: Optional[int] = None  # 0 for success, 1 for failure
+    run_signal: Optional[str] = None  # signal received on run failure
+    time_submit_exit: Optional[str] = None  # submit (exit) time
+    time_run: Optional[str] = None  # run start time
+    time_run_exit: Optional[str] = None  # run exit time
+    job_runner_call_no_lines = None  # line count in job runner call stdout
+
+    def __post_init__(self):
         self.pid = None
-        self.run_status: Optional[int] = None
-        self.run_signal: Optional[str] = None
-        self.time_submit_exit: Optional[str] = None
-        self.time_run: Optional[str] = None
-        self.time_run_exit: Optional[str] = None
-        self.job_runner_call_no_lines = None
-        self.messages = []
-
-        if attrs:
-            for key, value in attrs.items():
-                if key not in self.CONTEXT_ATTRIBUTES:
-                    raise ValueError('Invalid kwarg "%s"' % key)
-                setattr(self, key, value)
-
-    def update(self, other):
+        self.messages: List[str] = []
+
+    def update(self, other: 'JobPollContext') -> None:
         """Update my data from given file context."""
-        for i in self.__slots__:
+        for i in self.__dict__:
             setattr(self, i, getattr(other, i))
 
-    def get_summary_str(self):
+    def get_summary_str(self) -> str:
         """Return the poll context as a summary string delimited by "|"."""
-        ret = OrderedDict()
-        for key in self.CONTEXT_ATTRIBUTES:
-            value = getattr(self, key)
-            if key == 'job_log_dir' or value is None:
-                continue
-            ret[key] = value
+        ret = {
+            key: value
+            for key, value in asdict(self).items()
+            if key != 'job_log_dir' and value is not None
+        }
         return '%s|%s' % (self.job_log_dir, json.dumps(ret))
 
 
@@ -235,7 +218,7 @@ def jobs_poll(self, job_log_root, job_log_dirs):
             job_log_root = os.path.expandvars(job_log_root)
         self.configure_workflow_run_dir(job_log_root.rsplit(os.sep, 2)[0])
 
-        ctx_list = []  # Contexts for all relevant jobs
+        ctx_list: List[JobPollContext] = []  # Contexts for all relevant jobs
         ctx_list_by_job_runner = {}  # {job_runner_name1: [ctx1, ...], ...}
 
         for job_log_dir in job_log_dirs: