diff --git a/haystack/components/generators/chat/utils.py b/haystack/components/generators/chat/utils.py
new file mode 100644
index 00000000000..618816bb47a
--- /dev/null
+++ b/haystack/components/generators/chat/utils.py
@@ -0,0 +1,53 @@
+# SPDX-FileCopyrightText: 2022-present deepset GmbH <info@deepset.ai>
+#
+# SPDX-License-Identifier: Apache-2.0
+
+from haystack.components.generators.chat.types import ChatGenerator
+
+# The `generation_kwargs` key that caps a reply's length, per Chat Generator. Providers do not agree on a name and the
+# `ChatGenerator` protocol does not standardize it. Keyed by class name because most of these live in
+# `haystack-core-integrations` and cannot be imported here.
+_OUTPUT_TOKEN_LIMIT_KEYS = {
+    # Haystack
+    "OpenAIChatGenerator": "max_completion_tokens",
+    "AzureOpenAIChatGenerator": "max_completion_tokens",
+    "OpenAIResponsesChatGenerator": "max_output_tokens",
+    "AzureOpenAIResponsesChatGenerator": "max_output_tokens",
+    # haystack-core-integrations
+    "AIMLAPIChatGenerator": "max_tokens",
+    "AmazonBedrockChatGenerator": "maxTokens",
+    "AnthropicChatGenerator": "max_tokens",
+    "AnthropicFoundryChatGenerator": "max_tokens",
+    "AnthropicVertexChatGenerator": "max_tokens",
+    "CohereChatGenerator": "max_tokens",
+    "CometAPIChatGenerator": "max_tokens",
+    "EdenAIChatGenerator": "max_tokens",
+    "GoogleAIGeminiChatGenerator": "max_output_tokens",
+    "GoogleGenAIChatGenerator": "max_output_tokens",
+    "HuggingFaceAPIChatGenerator": "max_tokens",
+    "LiteLLMChatGenerator": "max_tokens",
+    "LlamaCppChatGenerator": "max_tokens",
+    "LlamaStackChatGenerator": "max_tokens",
+    "MistralChatGenerator": "max_tokens",
+    "NvidiaChatGenerator": "max_tokens",
+    "OllamaChatGenerator": "num_predict",
+    "OpenRouterChatGenerator": "max_tokens",
+    "OrcaRouterChatGenerator": "max_tokens",
+    "PerplexityChatGenerator": "max_output_tokens",
+    "STACKITChatGenerator": "max_tokens",
+    "TogetherAIChatGenerator": "max_tokens",
+    "TransformersChatGenerator": "max_new_tokens",
+    "VertexAIGeminiChatGenerator": "max_output_tokens",
+    "VLLMChatGenerator": "max_tokens",
+    "WatsonxChatGenerator": "max_new_tokens",
+}
+
+
+def _generator_output_token_limit_key(chat_generator: ChatGenerator) -> str | None:
+    """
+    Return the `generation_kwargs` key that limits a Chat Generator's output length.
+
+    :param chat_generator: The generator to look up.
+    :returns: The key the generator expects, or None when the generator is not recognized.
+    """
+    return _OUTPUT_TOKEN_LIMIT_KEYS.get(type(chat_generator).__name__)
diff --git a/test/components/generators/chat/test_utils.py b/test/components/generators/chat/test_utils.py
new file mode 100644
index 00000000000..97ab0cdd00e
--- /dev/null
+++ b/test/components/generators/chat/test_utils.py
@@ -0,0 +1,97 @@
+# SPDX-FileCopyrightText: 2022-present deepset GmbH <info@deepset.ai>
+#
+# SPDX-License-Identifier: Apache-2.0
+
+from typing import Any
+
+import pytest
+
+from haystack.components.generators.chat import (
+    AzureOpenAIChatGenerator,
+    AzureOpenAIResponsesChatGenerator,
+    OpenAIChatGenerator,
+    OpenAIResponsesChatGenerator,
+)
+from haystack.components.generators.chat.types import ChatGenerator
+from haystack.components.generators.chat.utils import _generator_output_token_limit_key
+from haystack.dataclasses import ChatMessage
+
+
+def integration_generator(class_name: str) -> ChatGenerator:
+    """
+    Return an object named `class_name` that satisfies `ChatGenerator`.
+
+    It stands in for a generator from `haystack-core-integrations`, which cannot be imported here. Lookup is by class
+    name, so the name is the only part that has to match; a rename on the integration side goes unnoticed.
+    """
+
+    def run(self: Any, messages: list[ChatMessage], **kwargs: Any) -> dict[str, Any]:
+        return {"replies": []}
+
+    generator: ChatGenerator = type(class_name, (), {"run": run})()
+    return generator
+
+
+class TestGeneratorOutputTokenLimitKey:
+    @pytest.mark.parametrize(
+        ("generator", "expected"),
+        [
+            pytest.param(OpenAIChatGenerator(), "max_completion_tokens", id="openai"),
+            pytest.param(
+                AzureOpenAIChatGenerator(azure_endpoint="https://test.openai.azure.com"),
+                "max_completion_tokens",
+                id="azure-openai",
+            ),
+            pytest.param(OpenAIResponsesChatGenerator(), "max_output_tokens", id="openai-responses"),
+            pytest.param(
+                AzureOpenAIResponsesChatGenerator(azure_endpoint="https://test.openai.azure.com"),
+                "max_output_tokens",
+                id="azure-openai-responses",
+            ),
+        ],
+    )
+    def test_recognizes_built_in_generators(self, generator, expected):
+        assert _generator_output_token_limit_key(chat_generator=generator) == expected
+
+    @pytest.mark.parametrize(
+        ("class_name", "expected"),
+        [
+            ("AIMLAPIChatGenerator", "max_tokens"),
+            ("AmazonBedrockChatGenerator", "maxTokens"),
+            ("AnthropicChatGenerator", "max_tokens"),
+            ("AnthropicFoundryChatGenerator", "max_tokens"),
+            ("AnthropicVertexChatGenerator", "max_tokens"),
+            ("CohereChatGenerator", "max_tokens"),
+            ("CometAPIChatGenerator", "max_tokens"),
+            ("EdenAIChatGenerator", "max_tokens"),
+            ("GoogleAIGeminiChatGenerator", "max_output_tokens"),
+            ("GoogleGenAIChatGenerator", "max_output_tokens"),
+            ("HuggingFaceAPIChatGenerator", "max_tokens"),
+            ("LiteLLMChatGenerator", "max_tokens"),
+            ("LlamaCppChatGenerator", "max_tokens"),
+            ("LlamaStackChatGenerator", "max_tokens"),
+            ("MistralChatGenerator", "max_tokens"),
+            ("NvidiaChatGenerator", "max_tokens"),
+            ("OllamaChatGenerator", "num_predict"),
+            ("OpenRouterChatGenerator", "max_tokens"),
+            ("OrcaRouterChatGenerator", "max_tokens"),
+            ("PerplexityChatGenerator", "max_output_tokens"),
+            ("STACKITChatGenerator", "max_tokens"),
+            ("TogetherAIChatGenerator", "max_tokens"),
+            ("TransformersChatGenerator", "max_new_tokens"),
+            ("VertexAIGeminiChatGenerator", "max_output_tokens"),
+            ("VLLMChatGenerator", "max_tokens"),
+            ("WatsonxChatGenerator", "max_new_tokens"),
+        ],
+    )
+    def test_recognizes_integration_generators(self, class_name, expected):
+        assert _generator_output_token_limit_key(chat_generator=integration_generator(class_name)) == expected
+
+    def test_an_unlisted_subclass_is_not_recognized(self):
+        class ProviderChatGenerator(OpenAIChatGenerator):
+            pass
+
+        assert _generator_output_token_limit_key(chat_generator=ProviderChatGenerator()) is None
+
+    def test_unknown_generator_is_not_recognized(self):
+        assert _generator_output_token_limit_key(chat_generator=integration_generator("MysteryChatGenerator")) is None