diff --git a/.gitignore b/.gitignore
index f58719a..47ef46d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -222,6 +222,9 @@ __marimo__/
 docs/*
 !docs/conf.py
 
+# Generated files
+experiment-*.log
+
 
 
 
diff --git a/.logging_config.yaml b/.logging_config.yaml
index 4af5d56..bf4c8c5 100644
--- a/.logging_config.yaml
+++ b/.logging_config.yaml
@@ -1,36 +1,56 @@
 version: 1
 
 custom_levels:
-  OBSERVATION: 25
-  ACTION: 26
+  OBSERVATION: 24
+  ACTION: 25
+  CHAT: 26
   LLM: 9
 
 formatters:
   # Console output
   colored:
-    (): "colorlog.ColoredFormatter"
+    class: colorlog.ColoredFormatter
     format: "{log_color}{asctime}.{msecs:03.0f} | {levelname:11} | {name:70} | {message}"
     style: "{"
     datefmt: "%H:%M:%S"
 
   # User-facing UI (structured JSON)
-  json_experiment:
-    (): "pythonjsonlogger.jsonlogger.JsonFormatter"
+  json:
+    class: pythonjsonlogger.jsonlogger.JsonFormatter
     format: "{name} {levelname} {levelno} {message} {created} {relativeCreated}"
     style: "{"
 
+  # Experiment stream for console and file output, with optional `role` field
+  experiment:
+    class: control_backend.logging.OptionalFieldFormatter
+    format: "%(asctime)s %(levelname)s %(role?)s %(message)s"
+    defaults:
+      role: "-"
+
+filters:
+  # Filter out any log records that have the extra field "partial" set to True, indicating that they
+  #  will be replaced later.
+  partial:
+    (): control_backend.logging.PartialFilter
+
 handlers:
   console:
     class: logging.StreamHandler
     level: DEBUG
     formatter: colored
+    filters: [partial]
     stream: ext://sys.stdout
   ui:
     class: zmq.log.handlers.PUBHandler
     level: LLM
-    formatter: json_experiment
+    formatter: json
+  file:
+    class: control_backend.logging.DatedFileHandler
+    formatter: experiment
+    filters: [partial]
+    file_prefix: experiment_logs/experiment
 
-# Level of external libraries
+# Level for external libraries
 root:
   level: WARN
   handlers: [console]
@@ -39,3 +59,6 @@ loggers:
   control_backend:
     level: LLM
     handlers: [ui]
+  experiment:
+    level: DEBUG
+    handlers: [ui, file]
diff --git a/src/control_backend/agents/base.py b/src/control_backend/agents/base.py
index ec50af5..beccdaa 100644
--- a/src/control_backend/agents/base.py
+++ b/src/control_backend/agents/base.py
@@ -1,9 +1,10 @@
 import logging
+from abc import ABC
 
 from control_backend.core.agent_system import BaseAgent as CoreBaseAgent
 
 
-class BaseAgent(CoreBaseAgent):
+class BaseAgent(CoreBaseAgent, ABC):
     """
     The primary base class for all implementation agents.
 
diff --git a/src/control_backend/core/config.py b/src/control_backend/core/config.py
index c4a4db7..c8af094 100644
--- a/src/control_backend/core/config.py
+++ b/src/control_backend/core/config.py
@@ -142,6 +142,18 @@ class SpeechModelSettings(BaseModel):
     openai_model_name: str = "small.en"
 
 
+class LoggingSettings(BaseModel):
+    """
+    Configuration for logging.
+
+    :ivar logging_config_file: Path to the logging configuration file.
+    :ivar experiment_logger_name: Name of the experiment logger, should match the logging config.
+    """
+
+    logging_config_file: str = ".logging_config.yaml"
+    experiment_logger_name: str = "experiment"
+
+
 class Settings(BaseSettings):
     """
     Global application settings.
@@ -163,6 +175,8 @@ class Settings(BaseSettings):
 
     ri_host: str = "localhost"
 
+    logging_settings: LoggingSettings = LoggingSettings()
+
     zmq_settings: ZMQSettings = ZMQSettings()
 
     agent_settings: AgentSettings = AgentSettings()
diff --git a/src/control_backend/logging/__init__.py b/src/control_backend/logging/__init__.py
index c97af40..a08e9b8 100644
--- a/src/control_backend/logging/__init__.py
+++ b/src/control_backend/logging/__init__.py
@@ -1 +1,4 @@
+from .dated_file_handler import DatedFileHandler as DatedFileHandler
+from .optional_field_formatter import OptionalFieldFormatter as OptionalFieldFormatter
+from .partial_filter import PartialFilter as PartialFilter
 from .setup_logging import setup_logging as setup_logging
diff --git a/src/control_backend/logging/dated_file_handler.py b/src/control_backend/logging/dated_file_handler.py
new file mode 100644
index 0000000..b927f9d
--- /dev/null
+++ b/src/control_backend/logging/dated_file_handler.py
@@ -0,0 +1,29 @@
+from datetime import datetime
+from logging import FileHandler
+from pathlib import Path
+
+
+class DatedFileHandler(FileHandler):
+    def __init__(self, file_prefix: str, **kwargs):
+        if not file_prefix:
+            raise ValueError("`file_prefix` argument cannot be empty.")
+        self._file_prefix = file_prefix
+        kwargs["filename"] = self._make_filename()
+        super().__init__(**kwargs)
+
+    def _make_filename(self) -> str:
+        filepath = Path(f"{self._file_prefix}-{datetime.now():%Y%m%d-%H%M%S}.log")
+        if not filepath.parent.is_dir():
+            filepath.parent.mkdir(parents=True, exist_ok=True)
+        return str(filepath)
+
+    def do_rollover(self):
+        self.acquire()
+        try:
+            if self.stream:
+                self.stream.close()
+
+            self.baseFilename = self._make_filename()
+            self.stream = self._open()
+        finally:
+            self.release()
diff --git a/src/control_backend/logging/optional_field_formatter.py b/src/control_backend/logging/optional_field_formatter.py
new file mode 100644
index 0000000..886e9a4
--- /dev/null
+++ b/src/control_backend/logging/optional_field_formatter.py
@@ -0,0 +1,67 @@
+import logging
+import re
+
+
+class OptionalFieldFormatter(logging.Formatter):
+    """
+    Logging formatter that supports optional fields marked by `?`.
+
+    Optional fields are denoted by placing a `?` after the field name inside
+    the parentheses, e.g., `%(role?)s`. If the field is not provided in the
+    log call's `extra` dict, it will use the default value from `defaults`
+    or `None` if no default is specified.
+
+    :param fmt: Format string with optional `%(name?)s` style fields.
+    :type fmt: str or None
+    :param datefmt: Date format string, passed to parent :class:`logging.Formatter`.
+    :type datefmt: str or None
+    :param style: Formatting style, must be '%'. Passed to parent.
+    :type style: str
+    :param defaults: Default values for optional fields when not provided.
+    :type defaults: dict or None
+
+    :example:
+
+        >>> formatter = OptionalFieldFormatter(
+        ...     fmt="%(asctime)s %(levelname)s %(role?)s %(message)s",
+        ...     defaults={"role": ""-""}
+        ... )
+        >>> handler = logging.StreamHandler()
+        >>> handler.setFormatter(formatter)
+        >>> logger = logging.getLogger(__name__)
+        >>> logger.addHandler(handler)
+        >>>
+        >>> logger.chat("Hello there!", extra={"role": "USER"})
+        2025-01-15 10:30:00 CHAT USER Hello there!
+        >>>
+        >>> logger.info("A logging message")
+        2025-01-15 10:30:01 INFO - A logging message
+
+    .. note::
+        Only `%`-style formatting is supported. The `{` and `$` styles are not
+        compatible with this formatter.
+
+    .. seealso::
+        :class:`logging.Formatter` for base formatter documentation.
+    """
+
+    # Match %(name?)s or %(name?)d etc.
+    OPTIONAL_PATTERN = re.compile(r"%\((\w+)\?\)([sdifFeEgGxXocrba%])")
+
+    def __init__(self, fmt=None, datefmt=None, style="%", defaults=None):
+        self.defaults = defaults or {}
+
+        self.optional_fields = set(self.OPTIONAL_PATTERN.findall(fmt or ""))
+
+        # Convert %(name?)s to %(name)s for standard formatting
+        normalized_fmt = self.OPTIONAL_PATTERN.sub(r"%(\1)\2", fmt or "")
+
+        super().__init__(normalized_fmt, datefmt, style)
+
+    def format(self, record):
+        for field, _ in self.optional_fields:
+            if not hasattr(record, field):
+                default = self.defaults.get(field, None)
+                setattr(record, field, default)
+
+        return super().format(record)
diff --git a/src/control_backend/logging/partial_filter.py b/src/control_backend/logging/partial_filter.py
new file mode 100644
index 0000000..1b121cb
--- /dev/null
+++ b/src/control_backend/logging/partial_filter.py
@@ -0,0 +1,10 @@
+import logging
+
+
+class PartialFilter(logging.Filter):
+    """
+    Class to filter any log records that have the "partial" attribute set to ``True``.
+    """
+
+    def filter(self, record):
+        return getattr(record, "partial", False) is not True
diff --git a/src/control_backend/logging/setup_logging.py b/src/control_backend/logging/setup_logging.py
index 05ae85a..7147dcc 100644
--- a/src/control_backend/logging/setup_logging.py
+++ b/src/control_backend/logging/setup_logging.py
@@ -37,7 +37,7 @@ def add_logging_level(level_name: str, level_num: int, method_name: str | None =
     setattr(logging, method_name, log_to_root)
 
 
-def setup_logging(path: str = ".logging_config.yaml") -> None:
+def setup_logging(path: str = settings.logging_settings.logging_config_file) -> None:
     """
     Setup logging configuration of the CB. Tries to load the logging configuration from a file,
     in which we specify custom loggers, formatters, handlers, etc.
@@ -65,7 +65,7 @@ def setup_logging(path: str = ".logging_config.yaml") -> None:
 
             # Patch ZMQ PUBHandler to know about custom levels
             if custom_levels:
-                for logger_name in ("control_backend",):
+                for logger_name in config.get("loggers", {}):
                     logger = logging.getLogger(logger_name)
                     for handler in logger.handlers:
                         if isinstance(handler, PUBHandler):
diff --git a/test/unit/logging/test_file_handler.py b/test/unit/logging/test_file_handler.py
new file mode 100644
index 0000000..9d1ee90
--- /dev/null
+++ b/test/unit/logging/test_file_handler.py
@@ -0,0 +1,18 @@
+from unittest.mock import MagicMock, patch
+
+from control_backend.logging.dated_file_handler import DatedFileHandler
+
+
+@patch("control_backend.logging.file_handler.DatedFileHandler._open")
+def test_reset(open_):
+    stream = MagicMock()
+    open_.return_value = stream
+
+    # A file should be opened when the logger is created
+    handler = DatedFileHandler(prefix="anything")
+    assert open_.call_count == 1
+
+    # Upon reset, the current file should be closed, and a new one should be opened
+    handler.do_rollover()
+    assert stream.close.call_count == 1
+    assert open_.call_count == 2
diff --git a/test/unit/logging/test_optional_field_formatter.py b/test/unit/logging/test_optional_field_formatter.py
new file mode 100644
index 0000000..ae75bd9
--- /dev/null
+++ b/test/unit/logging/test_optional_field_formatter.py
@@ -0,0 +1,218 @@
+import logging
+
+import pytest
+
+from control_backend.logging.optional_field_formatter import OptionalFieldFormatter
+
+
+@pytest.fixture
+def logger():
+    """Create a fresh logger for each test."""
+    logger = logging.getLogger(f"test_{id(object())}")
+    logger.setLevel(logging.DEBUG)
+    logger.handlers = []
+    return logger
+
+
+@pytest.fixture
+def log_output(logger):
+    """Capture log output and return a function to get it."""
+
+    class ListHandler(logging.Handler):
+        def __init__(self):
+            super().__init__()
+            self.records = []
+
+        def emit(self, record):
+            self.records.append(self.format(record))
+
+    handler = ListHandler()
+    logger.addHandler(handler)
+
+    def get_output():
+        return handler.records
+
+    return get_output
+
+
+def test_optional_field_present(logger, log_output):
+    """Optional field should appear when provided in extra."""
+    formatter = OptionalFieldFormatter("%(levelname)s - %(role?)s - %(message)s")
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test message", extra={"role": "user"})
+
+    assert log_output() == ["INFO - user - test message"]
+
+
+def test_optional_field_missing_no_default(logger, log_output):
+    """Missing optional field with no default should be None."""
+    formatter = OptionalFieldFormatter("%(levelname)s - %(role?)s - %(message)s")
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test message")
+
+    assert log_output() == ["INFO - None - test message"]
+
+
+def test_optional_field_missing_with_default(logger, log_output):
+    """Missing optional field should use provided default."""
+    formatter = OptionalFieldFormatter(
+        "%(levelname)s - %(role?)s - %(message)s", defaults={"role": "assistant"}
+    )
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test message")
+
+    assert log_output() == ["INFO - assistant - test message"]
+
+
+def test_optional_field_overrides_default(logger, log_output):
+    """Provided extra value should override default."""
+    formatter = OptionalFieldFormatter(
+        "%(levelname)s - %(role?)s - %(message)s", defaults={"role": "assistant"}
+    )
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test message", extra={"role": "user"})
+
+    assert log_output() == ["INFO - user - test message"]
+
+
+def test_multiple_optional_fields(logger, log_output):
+    """Multiple optional fields should work independently."""
+    formatter = OptionalFieldFormatter(
+        "%(levelname)s - %(role?)s - %(request_id?)s - %(message)s", defaults={"role": "assistant"}
+    )
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test", extra={"request_id": "123"})
+
+    assert log_output() == ["INFO - assistant - 123 - test"]
+
+
+def test_mixed_optional_and_required_fields(logger, log_output):
+    """Standard fields should work alongside optional fields."""
+    formatter = OptionalFieldFormatter("%(levelname)s %(name)s %(role?)s %(message)s")
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test", extra={"role": "user"})
+
+    output = log_output()[0]
+    assert "INFO" in output
+    assert "user" in output
+    assert "test" in output
+
+
+def test_no_optional_fields(logger, log_output):
+    """Formatter should work normally with no optional fields."""
+    formatter = OptionalFieldFormatter("%(levelname)s %(message)s")
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test message")
+
+    assert log_output() == ["INFO test message"]
+
+
+def test_integer_format_specifier(logger, log_output):
+    """Optional fields with %d specifier should work."""
+    formatter = OptionalFieldFormatter(
+        "%(levelname)s %(count?)d %(message)s", defaults={"count": 0}
+    )
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test", extra={"count": 42})
+
+    assert log_output() == ["INFO 42 test"]
+
+
+def test_float_format_specifier(logger, log_output):
+    """Optional fields with %f specifier should work."""
+    formatter = OptionalFieldFormatter(
+        "%(levelname)s %(duration?)f %(message)s", defaults={"duration": 0.0}
+    )
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test", extra={"duration": 1.5})
+
+    assert "1.5" in log_output()[0]
+
+
+def test_empty_string_default(logger, log_output):
+    """Empty string default should work."""
+    formatter = OptionalFieldFormatter("%(levelname)s %(role?)s %(message)s", defaults={"role": ""})
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test")
+
+    assert log_output() == ["INFO  test"]
+
+
+def test_none_format_string():
+    """None format string should not raise."""
+    formatter = OptionalFieldFormatter(fmt=None)
+    assert formatter.optional_fields == set()
+
+
+def test_optional_fields_parsed_correctly():
+    """Check that optional fields are correctly identified."""
+    formatter = OptionalFieldFormatter("%(asctime)s %(role?)s %(level?)d %(name)s")
+
+    assert formatter.optional_fields == {("role", "s"), ("level", "d")}
+
+
+def test_format_string_normalized():
+    """Check that ? is removed from format string."""
+    formatter = OptionalFieldFormatter("%(role?)s %(message)s")
+
+    assert "?" not in formatter._style._fmt
+    assert "%(role)s" in formatter._style._fmt
+
+
+def test_field_with_underscore(logger, log_output):
+    """Field names with underscores should work."""
+    formatter = OptionalFieldFormatter("%(levelname)s %(user_id?)s %(message)s")
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test", extra={"user_id": "abc123"})
+
+    assert log_output() == ["INFO abc123 test"]
+
+
+def test_field_with_numbers(logger, log_output):
+    """Field names with numbers should work."""
+    formatter = OptionalFieldFormatter("%(levelname)s %(field2?)s %(message)s")
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test", extra={"field2": "value"})
+
+    assert log_output() == ["INFO value test"]
+
+
+def test_multiple_log_calls(logger, log_output):
+    """Formatter should work correctly across multiple log calls."""
+    formatter = OptionalFieldFormatter(
+        "%(levelname)s %(role?)s %(message)s", defaults={"role": "other"}
+    )
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("first", extra={"role": "assistant"})
+    logger.info("second")
+    logger.info("third", extra={"role": "user"})
+
+    assert log_output() == [
+        "INFO assistant first",
+        "INFO other second",
+        "INFO user third",
+    ]
+
+
+def test_default_not_mutated(logger, log_output):
+    """Original defaults dict should not be mutated."""
+    defaults = {"role": "other"}
+    formatter = OptionalFieldFormatter("%(levelname)s %(role?)s %(message)s", defaults=defaults)
+    logger.handlers[0].setFormatter(formatter)
+
+    logger.info("test")
+
+    assert defaults == {"role": "other"}
diff --git a/test/unit/logging/test_partial_filter.py b/test/unit/logging/test_partial_filter.py
new file mode 100644
index 0000000..bd5ef10
--- /dev/null
+++ b/test/unit/logging/test_partial_filter.py
@@ -0,0 +1,83 @@
+import logging
+
+import pytest
+
+from control_backend.logging import PartialFilter
+
+
+@pytest.fixture
+def logger():
+    """Create a fresh logger for each test."""
+    logger = logging.getLogger(f"test_{id(object())}")
+    logger.setLevel(logging.DEBUG)
+    logger.handlers = []
+    return logger
+
+
+@pytest.fixture
+def log_output(logger):
+    """Capture log output and return a function to get it."""
+
+    class ListHandler(logging.Handler):
+        def __init__(self):
+            super().__init__()
+            self.records = []
+
+        def emit(self, record):
+            self.records.append(self.format(record))
+
+    handler = ListHandler()
+    handler.addFilter(PartialFilter())
+    handler.setFormatter(logging.Formatter("%(message)s"))
+    logger.addHandler(handler)
+
+    return lambda: handler.records
+
+
+def test_no_partial_attribute(logger, log_output):
+    """Records without partial attribute should pass through."""
+    logger.info("normal message")
+
+    assert log_output() == ["normal message"]
+
+
+def test_partial_true_filtered(logger, log_output):
+    """Records with partial=True should be filtered out."""
+    logger.info("partial message", extra={"partial": True})
+
+    assert log_output() == []
+
+
+def test_partial_false_passes(logger, log_output):
+    """Records with partial=False should pass through."""
+    logger.info("complete message", extra={"partial": False})
+
+    assert log_output() == ["complete message"]
+
+
+def test_partial_none_passes(logger, log_output):
+    """Records with partial=None should pass through."""
+    logger.info("message", extra={"partial": None})
+
+    assert log_output() == ["message"]
+
+
+def test_partial_truthy_value_passes(logger, log_output):
+    """
+    Records with truthy but non-True partial should pass through, that is, only when it's exactly
+    ``True`` should it pass.
+    """
+    logger.info("message", extra={"partial": "yes"})
+
+    assert log_output() == ["message"]
+
+
+def test_multiple_records_mixed(logger, log_output):
+    """Filter should handle mixed records correctly."""
+    logger.info("first")
+    logger.info("second", extra={"partial": True})
+    logger.info("third", extra={"partial": False})
+    logger.info("fourth", extra={"partial": True})
+    logger.info("fifth")
+
+    assert log_output() == ["first", "third", "fifth"]