diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index d601eaa..3d11d52 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,15 +1,7 @@
 repos:
--   repo: https://github.com/ambv/black
-    rev: 22.6.0
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.2.1
     hooks:
-    - id: black
--   repo: https://github.com/PyCQA/flake8
-    rev: 4.0.1
-    hooks:
-    - id: flake8
-      args: [--exclude=tests/*]
--   repo: https://github.com/pycqa/isort
-    rev: 5.12.0
-    hooks:
-      - id: isort
-        args: ["--profile", "black"]
\ No newline at end of file
+      - id: ruff
+        args: [ --fix ]
+      - id: ruff-format
diff --git a/CHANGES.md b/CHANGES.md
index 85c4939..fb7bb76 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,12 @@
 # Change Log
 
+## 0.0.6 (2024-02-15)
+
+* Use OpenAI v1.12.0.
+* Update OpenAI API calls.
+* Fix default value in greedy filter.
+* Update tests.
+
 ## 0.0.5 (2024-02-10)
 
 * Make Rasa an optional package.
diff --git a/README.md b/README.md
index a9f385c..f0c2a93 100644
--- a/README.md
+++ b/README.md
@@ -37,11 +37,11 @@ pip install -e .
 Once you have installed all dependencies you are ready to go with:
 ```python
 from nl2ltl import translate
-from nl2ltl.engines.rasa.core import RasaEngine
+from nl2ltl.engines.gpt.core import GPTEngine, Models
 from nl2ltl.filters.simple_filters import BasicFilter
 from nl2ltl.engines.utils import pretty
 
-engine = RasaEngine()
+engine = GPTEngine()
 filter = BasicFilter()
 utterance = "Eventually send me a Slack after receiving a Gmail"
 
@@ -65,7 +65,8 @@ For instance, Rasa requires a `.tar.gz` format trained model in the
 - [x] [Rasa](https://rasa.com/) intents/entities classifier (to use Rasa, please install it with `pip install -e ".[rasa]"`)
 - [ ] [Watson Assistant](https://www.ibm.com/products/watson-assistant) intents/entities classifier -- Planned
 
-To use GPT models you need to have the OPEN_API_KEY set as environment variable. To set it:
+**NOTE**: To use OpenAI GPT models don't forget to add the `OPEN_API_KEY` environment
+variable with:
 ```bash
 export OPENAI_API_KEY=your_api_key
 ```
@@ -118,7 +119,11 @@ ltl_formulas = translate(utterance, engine=my_engine, filter=my_filter)
 Contributions are welcome! Here's how to set up the development environment:
 - set up your preferred virtualenv environment
 - clone the repo: `git clone https://github.com/IBM/nl2ltl.git && cd nl2ltl`
+- install dependencies: `pip install -e .`
 - install dev dependencies: `pip install -e ".[dev]"`
+- install pre-commit: `pre-commit install`
+- sign-off your commits using the `-s` flag in the commit message to be compliant with 
+the [DCO](https://developercertificate.org/)
 
 ## Tests
 
diff --git a/nl2ltl/engines/gpt/core.py b/nl2ltl/engines/gpt/core.py
index 4cce8d0..4068b57 100644
--- a/nl2ltl/engines/gpt/core.py
+++ b/nl2ltl/engines/gpt/core.py
@@ -6,12 +6,11 @@
 
 """
 import json
-import os
 from enum import Enum
 from pathlib import Path
 from typing import Dict, Set
 
-import openai
+from openai import OpenAI
 from pylogics.syntax.base import Formula
 
 from nl2ltl.engines.base import Engine
@@ -19,7 +18,11 @@
 from nl2ltl.engines.gpt.output import GPTOutput, parse_gpt_output, parse_gpt_result
 from nl2ltl.filters.base import Filter
 
-openai.api_key = os.getenv("OPENAI_API_KEY")
+try:
+    client = OpenAI()
+except Exception:
+    client = None
+
 engine_root = ENGINE_ROOT
 DATA_DIR = engine_root / "data"
 PROMPT_PATH = engine_root / DATA_DIR / "prompt.json"
@@ -75,7 +78,7 @@ def _check_consistency(self) -> None:
 
     def __check_openai_version(self):
         """Check that the GPT tool is at the right version."""
-        is_right_version = openai.__version__ == "1.12.0"
+        is_right_version = client._version == "1.12.0"
         if not is_right_version:
             raise Exception(
                 "OpenAI needs to be at version 1.12.0. "
@@ -149,7 +152,7 @@ def _process_utterance(
     query = f"NL: {utterance}\n"
     messages = [{"role": "user", "content": prompt + query}]
     if operation_mode == OperationModes.CHAT.value:
-        prediction = openai.chat.completions.create(
+        prediction = client.chat.completions.create(
             model=model,
             messages=messages,
             temperature=temperature,
@@ -160,7 +163,7 @@ def _process_utterance(
             stop=["\n\n"],
         )
     else:
-        prediction = openai.completions.create(
+        prediction = client.completions.create(
             model=model,
             prompt=messages[0]["content"],
             temperature=temperature,
diff --git a/nl2ltl/engines/gpt/output.py b/nl2ltl/engines/gpt/output.py
index 5377933..b35ba31 100644
--- a/nl2ltl/engines/gpt/output.py
+++ b/nl2ltl/engines/gpt/output.py
@@ -40,7 +40,7 @@ def pattern(self) -> str:
                     Match,
                     re.search(
                         "PATTERN: (.*)\n",
-                        self.output["choices"][0]["message"]["content"],
+                        self.output.choices[0].message.content,
                     ),
                 ).group(1)
             )
@@ -48,7 +48,7 @@ def pattern(self) -> str:
             return str(
                 cast(
                     Match,
-                    re.search("PATTERN: (.*)\n", self.output["choices"][0]["text"]),
+                    re.search("PATTERN: (.*)\n", self.output.choices[0].text),
                 ).group(1)
             )
 
@@ -61,15 +61,13 @@ def entities(self) -> Tuple[str]:
             return tuple(
                 cast(
                     Match,
-                    re.search("SYMBOLS: (.*)", self.output["choices"][0]["message"]["content"]),
+                    re.search("SYMBOLS: (.*)", self.output.choices[0].message.content),
                 )
                 .group(1)
                 .split(", ")
             )
         else:
-            return tuple(
-                cast(Match, re.search("SYMBOLS: (.*)", self.output["choices"][0]["text"])).group(1).split(", ")
-            )
+            return tuple(cast(Match, re.search("SYMBOLS: (.*)", self.output.choices[0].text)).group(1).split(", "))
 
 
 def parse_gpt_output(gpt_output: dict, operation_mode: str) -> GPTOutput:
diff --git a/nl2ltl/filters/simple_filters.py b/nl2ltl/filters/simple_filters.py
index 506b40d..65ae13c 100644
--- a/nl2ltl/filters/simple_filters.py
+++ b/nl2ltl/filters/simple_filters.py
@@ -3,6 +3,7 @@
 
 from pylogics.syntax.base import Formula
 
+from nl2ltl.declare.base import Template
 from nl2ltl.filters.base import Filter
 from nl2ltl.filters.utils.conflicts import conflicts
 from nl2ltl.filters.utils.subsumptions import subsumptions
@@ -44,7 +45,7 @@ def enforce(output: Dict[Formula, float], entities: Dict[str, float], **kwargs)
         """
         result_set = set()
 
-        highest_scoring_formula = max(output, key=output.get)
+        highest_scoring_formula = max(output, key=output.get, default=Template)
         formula_conflicts = conflicts(highest_scoring_formula)
         formula_subsumptions = subsumptions(highest_scoring_formula)
 
diff --git a/pyproject.toml b/pyproject.toml
index 05f2528..5a5e947 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "nl2ltl"
-version = "0.0.5"
+version = "0.0.6"
 license = {file = "LICENSE"}
 authors = [
     { name = "Francesco Fuggitti", email = "francesco.fuggitti@gmail.com" },
@@ -34,7 +34,7 @@ classifiers = [
 
 dependencies = [
     "pylogics",
-    "openai"
+    "openai==1.12.0"
 ]
 
 [project.optional-dependencies]
diff --git a/tests/conftest.py b/tests/conftest.py
index 0e2ff51..ca9ca9b 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -13,8 +13,8 @@
 
 class UtterancesFixtures:
     utterances = [
-        "whenever I get a Slack, send a Gmail",
-        "Invite Sales employees to Thursday's meeting",
-        "If a new Eventbrite is created, alert me through Slack",
-        "send me a Slack whenever I get a Gmail",
+        "whenever I get a Slack, send a Gmail.",
+        "Invite Sales employees.",
+        "If a new Eventbrite is created, alert me through Slack.",
+        "send me a Slack whenever I get a Gmail.",
     ]
diff --git a/tests/test_gpt.py b/tests/test_gpt.py
index 643bfa6..841e13a 100644
--- a/tests/test_gpt.py
+++ b/tests/test_gpt.py
@@ -4,7 +4,7 @@
 import pytest
 
 from nl2ltl import translate
-from nl2ltl.engines.gpt.core import GPTEngine, Models
+from nl2ltl.engines.gpt.core import GPTEngine
 from nl2ltl.filters.simple_filters import BasicFilter, GreedyFilter
 
 from .conftest import UtterancesFixtures
@@ -18,7 +18,7 @@ def setup_class(cls):
         """Setup any state specific to the execution of the given class (which
         usually contains tests).
         """
-        cls.gpt_engine = GPTEngine(model=Models.GPT35_INSTRUCT.value)
+        cls.gpt_engine = GPTEngine()
         cls.basic_filter = BasicFilter()
         cls.greedy_filter = GreedyFilter()
 
diff --git a/tox.ini b/tox.ini
index 7c3febc..906f448 100644
--- a/tox.ini
+++ b/tox.ini
@@ -35,7 +35,7 @@ commands = ruff check .
 
 [testenv:ruff-check-apply]
 skip_install = True
-deps = ruff==0.1.9r
+deps = ruff==0.1.9
 commands = ruff check --fix --show-fixes .
 
 [testenv:ruff-format]