diff --git a/CHANGELOG.md b/CHANGELOG.md
index 95468a7..2319ba4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,16 @@ All notable changes to the AVP Python SDK are documented in this file.
 
 Format follows [Keep a Changelog](https://keepachangelog.com/). Versions follow [Semantic Versioning](https://semver.org/).
 
+## [Unreleased]
+
+### Changed
+
+- **Engine dependency floors** — `avp[hf]` now requires `transformers>=5.10.4` and `avp[vllm]` requires `vllm>=0.29.0` (with `huggingface-hub>=1.5,<2`). vLLM dropped its `transformers<5` cap in 0.24.0, so the `hf`, `vllm`, and `all` extras now resolve together on the current transformers 5.x line instead of forcing the old 4.x stack.
+
+### Fixed
+
+- **Protobuf gencode/runtime mismatch** — `src/avp/avp_pb2.py` was generated with protoc 6.31.1, whose `ValidateProtobufRuntimeVersion` guard requires a protobuf runtime `>=6.31.1`, while `autogen-core` (pulled in by the `autogen` extra and therefore by `all`) caps protobuf at the 5.29 line — so `import avp` raised `VersionError` in any environment containing that extra. The module is now regenerated with protoc 5.29 (gencode 5.29.0), the `protobuf` floor is raised to `>=5.29`, and `grpcio-tools` is pinned to `>=1.71.2,<1.72` so `make proto` cannot silently raise the runtime requirement again.
+
 ## [0.6.2] - 2026-04-26
 
 ### Added
diff --git a/Makefile b/Makefile
index 16e74db..40aefcf 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,8 @@
 .PHONY: proto test lint clean install
 
+# Regenerate avp_pb2.py. Keep grpcio-tools on the 5.29 gencode line
+# (>=1.71.2,<1.72): the autogen extra pins protobuf to 5.29.x, so a
+# newer protoc would emit gencode the runtime refuses to load.
 proto:
 	python -m grpc_tools.protoc \
 		-I proto \
diff --git a/pyproject.toml b/pyproject.toml
index 4b1ca17..3098d2b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,7 +23,7 @@ classifiers = [
 
 dependencies = [
     "numpy>=1.24",
-    "protobuf>=4.21",
+    "protobuf>=5.29",
     "zstandard>=0.21",
 ]
 
@@ -36,9 +36,9 @@ Changelog = "https://github.com/VectorArc/avp-python/blob/main/CHANGELOG.md"
 
 [project.optional-dependencies]
 # Engine connectors (pick one or more)
-hf = ["torch>=2.0", "transformers>=5.0"]
+hf = ["torch>=2.0", "transformers>=5.10.4"]
 huggingface = ["avp[hf]"]
-vllm = ["vllm>=0.17.0,<0.19.0", "safetensors>=0.4", "huggingface-hub>=1.0"]
+vllm = ["vllm>=0.29.0", "safetensors>=0.4", "huggingface-hub>=1.5,<2"]
 llamacpp = ["llama-cpp-python>=0.3", "gguf>=0.6"]
 ollama = ["llama-cpp-python>=0.3", "gguf>=0.6"]
 # Framework integrations (each requires HF engine)
@@ -57,7 +57,7 @@ dev = [
     "pytest>=7.0",
     "pytest-asyncio>=0.21",
     "ruff>=0.1",
-    "grpcio-tools>=1.59",
+    "grpcio-tools>=1.71.2,<1.72",
 ]
 
 [project.entry-points."vllm.general_plugins"]
diff --git a/src/avp/avp_pb2.py b/src/avp/avp_pb2.py
index 69aaa91..a73085d 100644
--- a/src/avp/avp_pb2.py
+++ b/src/avp/avp_pb2.py
@@ -2,7 +2,7 @@
 # Generated by the protocol buffer compiler.  DO NOT EDIT!
 # NO CHECKED-IN PROTOBUF GENCODE
 # source: avp.proto
-# Protobuf Python Version: 6.31.1
+# Protobuf Python Version: 5.29.0
 """Generated protocol buffer code."""
 from google.protobuf import descriptor as _descriptor
 from google.protobuf import descriptor_pool as _descriptor_pool
@@ -11,9 +11,9 @@
 from google.protobuf.internal import builder as _builder
 _runtime_version.ValidateProtobufRuntimeVersion(
     _runtime_version.Domain.PUBLIC,
-    6,
-    31,
-    1,
+    5,
+    29,
+    0,
     '',
     'avp.proto'
 )
@@ -24,7 +24,7 @@
 
 
 
-DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(b'\n\tavp.proto\x12\x03\x61vp\"\xdb\x03\n\x08Metadata\x12\x12\n\nsession_id\x18\x01 \x01(\t\x12\x17\n\x0fsource_agent_id\x18\x02 \x01(\t\x12\x17\n\x0ftarget_agent_id\x18\x03 \x01(\t\x12\x10\n\x08model_id\x18\x04 \x01(\t\x12\x12\n\nhidden_dim\x18\x05 \x01(\r\x12\x12\n\nnum_layers\x18\x06 \x01(\r\x12&\n\x0cpayload_type\x18\x07 \x01(\x0e\x32\x10.avp.PayloadType\x12\x1c\n\x05\x64type\x18\x08 \x01(\x0e\x32\r.avp.DataType\x12\x14\n\x0ctensor_shape\x18\t \x03(\r\x12$\n\x04mode\x18\n \x01(\x0e\x32\x16.avp.CommunicationMode\x12\x18\n\x0b\x63ompression\x18\x0b \x01(\tH\x00\x88\x01\x01\x12\x12\n\navp_map_id\x18\r \x01(\t\x12\'\n\x05\x65xtra\x18\x0e \x03(\x0b\x32\x18.avp.Metadata.ExtraEntry\x12\x1d\n\x10payload_checksum\x18\x0f \x01(\rH\x01\x88\x01\x01\x1a,\n\nExtraEntry\x12\x0b\n\x03key\x18\x01 \x01(\t\x12\r\n\x05value\x18\x02 \x01(\t:\x02\x38\x01\x42\x0e\n\x0c_compressionB\x13\n\x11_payload_checksumJ\x04\x08\x0c\x10\r\"\xcc\x01\n\x10TransmitResponse\x12\x0f\n\x07success\x18\x01 \x01(\x08\x12\x14\n\x07message\x18\x02 \x01(\tH\x00\x88\x01\x01\x12\x17\n\nrequest_id\x18\x03 \x01(\tH\x01\x88\x01\x01\x12/\n\x05\x65xtra\x18\x04 \x03(\x0b\x32 .avp.TransmitResponse.ExtraEntry\x1a,\n\nExtraEntry\x12\x0b\n\x03key\x18\x01 \x01(\t\x12\r\n\x05value\x18\x02 \x01(\t:\x02\x38\x01\x42\n\n\x08_messageB\r\n\x0b_request_id*<\n\x0bPayloadType\x12\x10\n\x0cHIDDEN_STATE\x10\x00\x12\x0c\n\x08KV_CACHE\x10\x01\x12\r\n\tEMBEDDING\x10\x02*.\n\x11\x43ommunicationMode\x12\n\n\x06LATENT\x10\x00\x12\r\n\tJSON_MODE\x10\x01*<\n\x08\x44\x61taType\x12\x0b\n\x07\x46LOAT32\x10\x00\x12\x0b\n\x07\x46LOAT16\x10\x01\x12\x0c\n\x08\x42\x46LOAT16\x10\x02\x12\x08\n\x04INT8\x10\x03\x62\x06proto3')
+DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(b'\n\tavp.proto\x12\x03\x61vp\"\xdb\x03\n\x08Metadata\x12\x12\n\nsession_id\x18\x01 \x01(\t\x12\x17\n\x0fsource_agent_id\x18\x02 \x01(\t\x12\x17\n\x0ftarget_agent_id\x18\x03 \x01(\t\x12\x10\n\x08model_id\x18\x04 \x01(\t\x12\x12\n\nhidden_dim\x18\x05 \x01(\r\x12\x12\n\nnum_layers\x18\x06 \x01(\r\x12&\n\x0cpayload_type\x18\x07 \x01(\x0e\x32\x10.avp.PayloadType\x12\x1c\n\x05\x64type\x18\x08 \x01(\x0e\x32\r.avp.DataType\x12\x14\n\x0ctensor_shape\x18\t \x03(\r\x12$\n\x04mode\x18\n \x01(\x0e\x32\x16.avp.CommunicationMode\x12\x18\n\x0b\x63ompression\x18\x0b \x01(\tH\x00\x88\x01\x01\x12\x12\n\navp_map_id\x18\r \x01(\t\x12\'\n\x05\x65xtra\x18\x0e \x03(\x0b\x32\x18.avp.Metadata.ExtraEntry\x12\x1d\n\x10payload_checksum\x18\x0f \x01(\rH\x01\x88\x01\x01\x1a,\n\nExtraEntry\x12\x0b\n\x03key\x18\x01 \x01(\t\x12\r\n\x05value\x18\x02 \x01(\t:\x02\x38\x01\x42\x0e\n\x0c_compressionB\x13\n\x11_payload_checksumJ\x04\x08\x0c\x10\r\"\xcc\x01\n\x10TransmitResponse\x12\x0f\n\x07success\x18\x01 \x01(\x08\x12\x14\n\x07message\x18\x02 \x01(\tH\x00\x88\x01\x01\x12\x17\n\nrequest_id\x18\x03 \x01(\tH\x01\x88\x01\x01\x12/\n\x05\x65xtra\x18\x04 \x03(\x0b\x32 .avp.TransmitResponse.ExtraEntry\x1a,\n\nExtraEntry\x12\x0b\n\x03key\x18\x01 \x01(\t\x12\r\n\x05value\x18\x02 \x01(\t:\x02\x38\x01\x42\n\n\x08_messageB\r\n\x0b_request_id*-\n\x0bPayloadType\x12\x10\n\x0cHIDDEN_STATE\x10\x00\x12\x0c\n\x08KV_CACHE\x10\x01*.\n\x11\x43ommunicationMode\x12\n\n\x06LATENT\x10\x00\x12\r\n\tJSON_MODE\x10\x01*<\n\x08\x44\x61taType\x12\x0b\n\x07\x46LOAT32\x10\x00\x12\x0b\n\x07\x46LOAT16\x10\x01\x12\x0c\n\x08\x42\x46LOAT16\x10\x02\x12\x08\n\x04INT8\x10\x03\x62\x06proto3')
 
 _globals = globals()
 _builder.BuildMessageAndEnumDescriptors(DESCRIPTOR, _globals)
@@ -36,11 +36,11 @@
   _globals['_TRANSMITRESPONSE_EXTRAENTRY']._loaded_options = None
   _globals['_TRANSMITRESPONSE_EXTRAENTRY']._serialized_options = b'8\001'
   _globals['_PAYLOADTYPE']._serialized_start=703
-  _globals['_PAYLOADTYPE']._serialized_end=763
-  _globals['_COMMUNICATIONMODE']._serialized_start=765
-  _globals['_COMMUNICATIONMODE']._serialized_end=811
-  _globals['_DATATYPE']._serialized_start=813
-  _globals['_DATATYPE']._serialized_end=873
+  _globals['_PAYLOADTYPE']._serialized_end=748
+  _globals['_COMMUNICATIONMODE']._serialized_start=750
+  _globals['_COMMUNICATIONMODE']._serialized_end=796
+  _globals['_DATATYPE']._serialized_start=798
+  _globals['_DATATYPE']._serialized_end=858
   _globals['_METADATA']._serialized_start=19
   _globals['_METADATA']._serialized_end=494
   _globals['_METADATA_EXTRAENTRY']._serialized_start=407