diff --git a/libs/core/langchain_core/callbacks/base.py b/libs/core/langchain_core/callbacks/base.py
index 23419319040..6e4df3dd891 100644
--- a/libs/core/langchain_core/callbacks/base.py
+++ b/libs/core/langchain_core/callbacks/base.py
@@ -64,7 +64,7 @@ class LLMManagerMixin:
 
     def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         run_id: UUID,
@@ -79,7 +79,7 @@ class LLMManagerMixin:
         For both chat models and non-chat models (legacy text completion LLMs).
 
         Args:
-            token: The new token.
+            token: The new token, or a list of content blocks.
             chunk: The new generated chunk, containing content and other information.
             run_id: The ID of the current run.
             parent_run_id: The ID of the parent run.
@@ -631,7 +631,7 @@ class AsyncCallbackHandler(BaseCallbackHandler):
 
     async def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         run_id: UUID,
@@ -644,7 +644,7 @@ class AsyncCallbackHandler(BaseCallbackHandler):
         For both chat models and non-chat models (legacy text completion LLMs).
 
         Args:
-            token: The new token.
+            token: The new token, or a list of content blocks.
             chunk: The new generated chunk, containing content and other information.
             run_id: The ID of the current run.
             parent_run_id: The ID of the parent run.
diff --git a/libs/core/langchain_core/callbacks/manager.py b/libs/core/langchain_core/callbacks/manager.py
index 40fd907272a..8d46f74eea2 100644
--- a/libs/core/langchain_core/callbacks/manager.py
+++ b/libs/core/langchain_core/callbacks/manager.py
@@ -668,7 +668,7 @@ class CallbackManagerForLLMRun(RunManager, LLMManagerMixin):
 
     def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         **kwargs: Any,
@@ -676,7 +676,7 @@ class CallbackManagerForLLMRun(RunManager, LLMManagerMixin):
         """Run when LLM generates a new token.
 
         Args:
-            token: The new token.
+            token: The new token, or a list of content blocks.
             chunk: The chunk.
             **kwargs: Additional keyword arguments.
 
@@ -787,7 +787,7 @@ class AsyncCallbackManagerForLLMRun(AsyncRunManager, LLMManagerMixin):
 
     async def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         **kwargs: Any,
@@ -795,7 +795,7 @@ class AsyncCallbackManagerForLLMRun(AsyncRunManager, LLMManagerMixin):
         """Run when LLM generates a new token.
 
         Args:
-            token: The new token.
+            token: The new token, or a list of content blocks.
             chunk: The chunk.
             **kwargs: Additional keyword arguments.
 
diff --git a/libs/core/langchain_core/callbacks/streaming_stdout.py b/libs/core/langchain_core/callbacks/streaming_stdout.py
index 920fef80bde..5cba233ee5a 100644
--- a/libs/core/langchain_core/callbacks/streaming_stdout.py
+++ b/libs/core/langchain_core/callbacks/streaming_stdout.py
@@ -47,14 +47,16 @@ class StreamingStdOutCallbackHandler(BaseCallbackHandler):
         """
 
     @override
-    def on_llm_new_token(self, token: str, **kwargs: Any) -> None:
+    def on_llm_new_token(
+        self, token: str | list[str | dict[str, Any]], **kwargs: Any
+    ) -> None:
         """Run on new LLM token. Only available when streaming is enabled.
 
         Args:
-            token: The new token.
+            token: The new token, or a list of content blocks.
             **kwargs: Additional keyword arguments.
         """
-        sys.stdout.write(token)
+        sys.stdout.write(str(token))
         sys.stdout.flush()
 
     def on_llm_end(self, response: LLMResult, **kwargs: Any) -> None:
diff --git a/libs/core/langchain_core/language_models/chat_models.py b/libs/core/langchain_core/language_models/chat_models.py
index cc946a919be..7c21d12110f 100644
--- a/libs/core/langchain_core/language_models/chat_models.py
+++ b/libs/core/langchain_core/language_models/chat_models.py
@@ -792,9 +792,7 @@ class BaseChatModel(BaseLanguageModel[AIMessage], ABC):
                                 index += 1
                             if "index" not in block:
                                 block["index"] = index
-                    run_manager.on_llm_new_token(
-                        cast("str", chunk.message.content), chunk=chunk
-                    )
+                    run_manager.on_llm_new_token(chunk.message.content, chunk=chunk)
                     chunks.append(chunk)
                     yield cast("AIMessageChunk", chunk.message)
                     yielded = True
@@ -927,9 +925,7 @@ class BaseChatModel(BaseLanguageModel[AIMessage], ABC):
                             index += 1
                         if "index" not in block:
                             block["index"] = index
-                await run_manager.on_llm_new_token(
-                    cast("str", chunk.message.content), chunk=chunk
-                )
+                await run_manager.on_llm_new_token(chunk.message.content, chunk=chunk)
                 chunks.append(chunk)
                 yield cast("AIMessageChunk", chunk.message)
                 yielded = True
@@ -1972,9 +1968,7 @@ class BaseChatModel(BaseLanguageModel[AIMessage], ABC):
                 if run_manager:
                     if chunk.message.id is None:
                         chunk.message.id = run_id
-                    run_manager.on_llm_new_token(
-                        cast("str", chunk.message.content), chunk=chunk
-                    )
+                    run_manager.on_llm_new_token(chunk.message.content, chunk=chunk)
                 chunks.append(chunk)
                 yielded = True
 
@@ -2130,7 +2124,7 @@ class BaseChatModel(BaseLanguageModel[AIMessage], ABC):
                     if chunk.message.id is None:
                         chunk.message.id = run_id
                     await run_manager.on_llm_new_token(
-                        cast("str", chunk.message.content), chunk=chunk
+                        chunk.message.content, chunk=chunk
                     )
                 chunks.append(chunk)
                 yielded = True
diff --git a/libs/core/langchain_core/tracers/base.py b/libs/core/langchain_core/tracers/base.py
index 0c49530a30b..70ba436c8d2 100644
--- a/libs/core/langchain_core/tracers/base.py
+++ b/libs/core/langchain_core/tracers/base.py
@@ -149,7 +149,7 @@ class BaseTracer(_TracerCore, BaseCallbackHandler, ABC):
     @override
     def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         run_id: UUID,
@@ -161,7 +161,7 @@ class BaseTracer(_TracerCore, BaseCallbackHandler, ABC):
         Only available when streaming is enabled.
 
         Args:
-            token: The token.
+            token: The token, or a list of content blocks for structured output.
             chunk: The chunk.
             run_id: The run ID.
             parent_run_id: The parent run ID.
@@ -645,7 +645,7 @@ class AsyncBaseTracer(_TracerCore, AsyncCallbackHandler, ABC):
     @override
     async def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         run_id: UUID,
@@ -919,7 +919,7 @@ class AsyncBaseTracer(_TracerCore, AsyncCallbackHandler, ABC):
     async def _on_llm_new_token(
         self,
         run: Run,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         chunk: GenerationChunk | ChatGenerationChunk | None,
     ) -> None:
         """Process new LLM token."""
diff --git a/libs/core/langchain_core/tracers/core.py b/libs/core/langchain_core/tracers/core.py
index c6f6cca167c..5e073259d98 100644
--- a/libs/core/langchain_core/tracers/core.py
+++ b/libs/core/langchain_core/tracers/core.py
@@ -242,7 +242,7 @@ class _TracerCore(ABC):
 
     def _llm_run_with_token_event(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         run_id: UUID,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         parent_run_id: UUID | None = None,
@@ -602,14 +602,14 @@ class _TracerCore(ABC):
     def _on_llm_new_token(
         self,
         run: Run,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         chunk: GenerationChunk | ChatGenerationChunk | None,
     ) -> Coroutine[Any, Any, None] | None:
         """Process new LLM token.
 
         Args:
             run: The LLM run.
-            token: The new token.
+            token: The new token, or a list of content blocks.
             chunk: Optional chunk.
         """
         _ = (run, token, chunk)
diff --git a/libs/core/langchain_core/tracers/event_stream.py b/libs/core/langchain_core/tracers/event_stream.py
index cba55b8bb9c..7d5db9cc8f6 100644
--- a/libs/core/langchain_core/tracers/event_stream.py
+++ b/libs/core/langchain_core/tracers/event_stream.py
@@ -429,7 +429,7 @@ class _AstreamEventsCallbackHandler(
     @override
     async def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         run_id: UUID,
@@ -465,7 +465,8 @@ class _AstreamEventsCallbackHandler(
         elif run_info["run_type"] == "llm":
             event = "on_llm_stream"
             if chunk is None:
-                chunk_ = GenerationChunk(text=token)
+                text = token if isinstance(token, str) else ""
+                chunk_ = GenerationChunk(text=text)
             else:
                 chunk_ = cast("GenerationChunk", chunk)
         else:
diff --git a/libs/core/langchain_core/tracers/langchain.py b/libs/core/langchain_core/tracers/langchain.py
index 6295a2f034b..9b3bbd37527 100644
--- a/libs/core/langchain_core/tracers/langchain.py
+++ b/libs/core/langchain_core/tracers/langchain.py
@@ -359,7 +359,7 @@ class LangChainTracer(BaseTracer):
     @override
     def _llm_run_with_token_event(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         run_id: UUID,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         parent_run_id: UUID | None = None,
diff --git a/libs/core/langchain_core/tracers/log_stream.py b/libs/core/langchain_core/tracers/log_stream.py
index ebafc14b0e9..cf94189c9d5 100644
--- a/libs/core/langchain_core/tracers/log_stream.py
+++ b/libs/core/langchain_core/tracers/log_stream.py
@@ -537,7 +537,7 @@ class LogStreamCallbackHandler(BaseTracer, _StreamingCallbackHandler[Any]):
     def _on_llm_new_token(
         self,
         run: Run,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         chunk: GenerationChunk | ChatGenerationChunk | None,
     ) -> None:
         """Process new LLM token."""
diff --git a/libs/core/tests/benchmarks/test_async_callbacks.py b/libs/core/tests/benchmarks/test_async_callbacks.py
index f6774ae3620..8f5582a96a7 100644
--- a/libs/core/tests/benchmarks/test_async_callbacks.py
+++ b/libs/core/tests/benchmarks/test_async_callbacks.py
@@ -33,7 +33,7 @@ class MyCustomAsyncHandler(AsyncCallbackHandler):
     @override
     async def on_llm_new_token(
         self,
-        token: str,
+        token: str | list[str | dict[str, Any]],
         *,
         chunk: GenerationChunk | ChatGenerationChunk | None = None,
         run_id: UUID,
diff --git a/libs/core/tests/unit_tests/fake/test_fake_chat_model.py b/libs/core/tests/unit_tests/fake/test_fake_chat_model.py
index bf5629a12c5..786c7bcfea3 100644
--- a/libs/core/tests/unit_tests/fake/test_fake_chat_model.py
+++ b/libs/core/tests/unit_tests/fake/test_fake_chat_model.py
@@ -182,7 +182,7 @@ async def test_callback_handlers() -> None:
         @override
         async def on_llm_new_token(
             self,
-            token: str,
+            token: str | list[str | dict[str, Any]],
             *,
             chunk: GenerationChunk | ChatGenerationChunk | None = None,
             run_id: UUID,
@@ -190,7 +190,8 @@ async def test_callback_handlers() -> None:
             tags: list[str] | None = None,
             **kwargs: Any,
         ) -> None:
-            self.store.append(token)
+            if isinstance(token, str):
+                self.store.append(token)
 
     infinite_cycle = cycle(
         [
diff --git a/libs/langchain/Makefile b/libs/langchain/Makefile
index 421d4a5b755..92f0dcaa59e 100644
--- a/libs/langchain/Makefile
+++ b/libs/langchain/Makefile
@@ -52,19 +52,22 @@ lint_diff format_diff: PYTHON_FILES=$(shell git diff --relative=libs/langchain -
 lint_package: PYTHON_FILES=langchain_classic
 lint_tests: PYTHON_FILES=tests
 lint_tests: MYPY_CACHE=.mypy_cache_test
+UV_RUN_LINT = uv run --all-groups
+UV_RUN_TYPE = uv run --all-groups
+lint_package lint_tests: UV_RUN_LINT = uv run --group lint
 
 lint lint_diff lint_package lint_tests:
 	./scripts/lint_imports.sh
-	[ "$(PYTHON_FILES)" = "" ] || uv run --group lint --group typing ruff check $(PYTHON_FILES)
-	[ "$(PYTHON_FILES)" = "" ] || uv run --group lint --group typing ruff format $(PYTHON_FILES) --diff
-	[ "$(PYTHON_FILES)" = "" ] || mkdir -p $(MYPY_CACHE) && uv run --group lint --group typing mypy $(PYTHON_FILES) --cache-dir $(MYPY_CACHE)
+	[ "$(PYTHON_FILES)" = "" ] || $(UV_RUN_LINT) ruff check $(PYTHON_FILES)
+	[ "$(PYTHON_FILES)" = "" ] || $(UV_RUN_LINT) ruff format $(PYTHON_FILES) --diff
+	[ "$(PYTHON_FILES)" = "" ] || mkdir -p $(MYPY_CACHE) && $(UV_RUN_TYPE) mypy $(PYTHON_FILES) --cache-dir $(MYPY_CACHE)
 
 type:
-	mkdir -p $(MYPY_CACHE) && uv run --group lint --group typing mypy $(PYTHON_FILES) --cache-dir $(MYPY_CACHE)
+	mkdir -p $(MYPY_CACHE) && $(UV_RUN_TYPE) mypy $(PYTHON_FILES) --cache-dir $(MYPY_CACHE)
 
 format format_diff:
-	[ "$(PYTHON_FILES)" = "" ] || uv run --group lint --group typing ruff format $(PYTHON_FILES)
-	[ "$(PYTHON_FILES)" = "" ] || uv run --group lint --group typing ruff check --fix $(PYTHON_FILES)
+	[ "$(PYTHON_FILES)" = "" ] || $(UV_RUN_LINT) ruff format $(PYTHON_FILES)
+	[ "$(PYTHON_FILES)" = "" ] || $(UV_RUN_LINT) ruff check --fix $(PYTHON_FILES)
 
 ######################
 # HELP
diff --git a/libs/langchain/langchain_classic/callbacks/streaming_aiter.py b/libs/langchain/langchain_classic/callbacks/streaming_aiter.py
index 0811e86a3e7..cb0ab1f86dc 100644
--- a/libs/langchain/langchain_classic/callbacks/streaming_aiter.py
+++ b/libs/langchain/langchain_classic/callbacks/streaming_aiter.py
@@ -39,9 +39,12 @@ class AsyncIteratorCallbackHandler(AsyncCallbackHandler):
         self.done.clear()
 
     @override
-    async def on_llm_new_token(self, token: str, **kwargs: Any) -> None:
-        if token is not None and token != "":
-            self.queue.put_nowait(token)
+    async def on_llm_new_token(
+        self, token: str | list[str | dict[str, Any]], **kwargs: Any
+    ) -> None:
+        token_str = token if isinstance(token, str) else str(token)
+        if token_str != "":
+            self.queue.put_nowait(token_str)
 
     @override
     async def on_llm_end(self, response: LLMResult, **kwargs: Any) -> None:
diff --git a/libs/langchain/langchain_classic/callbacks/streaming_aiter_final_only.py b/libs/langchain/langchain_classic/callbacks/streaming_aiter_final_only.py
index 744475e6628..37b3ce93a9a 100644
--- a/libs/langchain/langchain_classic/callbacks/streaming_aiter_final_only.py
+++ b/libs/langchain/langchain_classic/callbacks/streaming_aiter_final_only.py
@@ -81,9 +81,13 @@ class AsyncFinalIteratorCallbackHandler(AsyncIteratorCallbackHandler):
             self.done.set()
 
     @override
-    async def on_llm_new_token(self, token: str, **kwargs: Any) -> None:
+    async def on_llm_new_token(
+        self, token: str | list[str | dict[str, Any]], **kwargs: Any
+    ) -> None:
+        token_str = token if isinstance(token, str) else str(token)
+
         # Remember the last n tokens, where n = len(answer_prefix_tokens)
-        self.append_to_last_tokens(token)
+        self.append_to_last_tokens(token_str)
 
         # Check if the last n tokens match the answer_prefix_tokens list ...
         if self.check_if_answer_reached():
@@ -95,4 +99,4 @@ class AsyncFinalIteratorCallbackHandler(AsyncIteratorCallbackHandler):
 
         # If yes, then put tokens from now on
         if self.answer_reached:
-            self.queue.put_nowait(token)
+            self.queue.put_nowait(token_str)
diff --git a/libs/langchain/langchain_classic/callbacks/streaming_stdout_final_only.py b/libs/langchain/langchain_classic/callbacks/streaming_stdout_final_only.py
index e8eee519b3e..62ef56ddbdd 100644
--- a/libs/langchain/langchain_classic/callbacks/streaming_stdout_final_only.py
+++ b/libs/langchain/langchain_classic/callbacks/streaming_stdout_final_only.py
@@ -76,10 +76,14 @@ class FinalStreamingStdOutCallbackHandler(StreamingStdOutCallbackHandler):
         self.answer_reached = False
 
     @override
-    def on_llm_new_token(self, token: str, **kwargs: Any) -> None:
+    def on_llm_new_token(
+        self, token: str | list[str | dict[str, Any]], **kwargs: Any
+    ) -> None:
         """Run on new LLM token. Only available when streaming is enabled."""
+        token_str = token if isinstance(token, str) else str(token)
+
         # Remember the last n tokens, where n = len(answer_prefix_tokens)
-        self.append_to_last_tokens(token)
+        self.append_to_last_tokens(token_str)
 
         # Check if the last n tokens match the answer_prefix_tokens list ...
         if self.check_if_answer_reached():
@@ -92,5 +96,5 @@ class FinalStreamingStdOutCallbackHandler(StreamingStdOutCallbackHandler):
 
         # ... if yes, then print tokens from now on
         if self.answer_reached:
-            sys.stdout.write(token)
+            sys.stdout.write(token_str)
             sys.stdout.flush()
diff --git a/libs/langchain/tests/unit_tests/llms/test_fake_chat_model.py b/libs/langchain/tests/unit_tests/llms/test_fake_chat_model.py
index 88cd91c3d13..57a2f884985 100644
--- a/libs/langchain/tests/unit_tests/llms/test_fake_chat_model.py
+++ b/libs/langchain/tests/unit_tests/llms/test_fake_chat_model.py
@@ -173,7 +173,7 @@ async def test_callback_handlers() -> None:
         @override
         async def on_llm_new_token(
             self,
-            token: str,
+            token: str | list[str | dict[str, Any]],
             *,
             chunk: GenerationChunk | ChatGenerationChunk | None = None,
             run_id: UUID,
@@ -181,7 +181,8 @@ async def test_callback_handlers() -> None:
             tags: list[str] | None = None,
             **kwargs: Any,
         ) -> None:
-            self.store.append(token)
+            if isinstance(token, str):
+                self.store.append(token)
 
     infinite_cycle = cycle(
         [
diff --git a/libs/partners/anthropic/langchain_anthropic/output_parsers.py b/libs/partners/anthropic/langchain_anthropic/output_parsers.py
index 57e2121c5e5..60b189de1d6 100644
--- a/libs/partners/anthropic/langchain_anthropic/output_parsers.py
+++ b/libs/partners/anthropic/langchain_anthropic/output_parsers.py
@@ -77,7 +77,7 @@ def _extract_tool_calls_from_message(message: AIMessage) -> list[ToolCall]:
     return extract_tool_calls(message.content)
 
 
-def extract_tool_calls(content: str | list[str | dict]) -> list[ToolCall]:
+def extract_tool_calls(content: str | list[str | dict[str, Any]]) -> list[ToolCall]:
     """Extract tool calls from a list of content blocks."""
     if isinstance(content, list):
         tool_calls = []
diff --git a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
index fe1f217f851..0dbdceb483e 100644
--- a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
@@ -737,7 +737,7 @@ def test__format_messages_with_tool_calls() -> None:
     assert expected == actual
 
     # Check handling of empty AIMessage
-    empty_contents: list[str | list[str | dict]] = ["", []]
+    empty_contents: list[str | list[str | dict[str, Any]]] = ["", []]
     for empty_content in empty_contents:
         ## Permit message in final position
         _, anthropic_messages = _format_messages([human, AIMessage(empty_content)])
diff --git a/libs/partners/mistralai/langchain_mistralai/_compat.py b/libs/partners/mistralai/langchain_mistralai/_compat.py
index f716300dccc..16f525791f7 100644
--- a/libs/partners/mistralai/langchain_mistralai/_compat.py
+++ b/libs/partners/mistralai/langchain_mistralai/_compat.py
@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+from typing import Any
+
 from langchain_core.messages import AIMessage, AIMessageChunk
 from langchain_core.messages import content as types
 from langchain_core.messages.block_translators import register_translator
@@ -10,7 +12,7 @@ from langchain_core.messages.block_translators import register_translator
 def _convert_from_v1_to_mistral(
     content: list[types.ContentBlock],
     model_provider: str | None,
-) -> str | list[str | dict]:
+) -> str | list[str | dict[str, Any]]:
     new_content: list = []
     for block in content:
         if block["type"] == "text":
diff --git a/libs/partners/mistralai/tests/unit_tests/test_chat_models.py b/libs/partners/mistralai/tests/unit_tests/test_chat_models.py
index 90be8938812..38de8cdb074 100644
--- a/libs/partners/mistralai/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/mistralai/tests/unit_tests/test_chat_models.py
@@ -339,8 +339,11 @@ async def mock_chat_astream(*args: Any, **kwargs: Any) -> AsyncGenerator:
 class MyCustomHandler(BaseCallbackHandler):
     last_token: str = ""
 
-    def on_llm_new_token(self, token: str, **kwargs: Any) -> None:
-        self.last_token = token
+    def on_llm_new_token(
+        self, token: str | list[str | dict[str, Any]], **kwargs: Any
+    ) -> None:
+        if isinstance(token, str):
+            self.last_token = token
 
 
 @patch(