diff --git a/Makefile b/Makefile
index f00279f..c6633ba 100644
--- a/Makefile
+++ b/Makefile
@@ -16,6 +16,10 @@ check:
 		-fsyntax-only -Iinclude test/ptoas_linx_type_compat.cpp
 	$(CXX) -std=c++20 -D__linx -include test/linx_host_type_shim.hpp \
 		-fsyntax-only -Iinclude test/pto0583_contract.cpp
+	$(CXX) -std=c++20 -D__linx -fsyntax-only -Iinclude \
+		test/linx_group_runtime_api.cpp
+	$(CC) -std=c11 -D__linx -fsyntax-only -Iinclude \
+		test/linx_group_runtime_api.c
 	bash -n test/tileop_api/compile.all test/tileop_api/run_negatives.sh \
 		test/tileop_api/verify_pto0583_asm.sh \
 		test/tileop_api/verify_target_cxx_frontend.sh
diff --git a/README.md b/README.md
index b605823..2c80f2f 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@ canonical aliases.
 - [Comparison operations](docs/tileop-usage/cmp.md)
 - [Sorting operations](docs/tileop-usage/sort.md)
 - [Fixed-point matrix wrappers](docs/tileop-usage/tmatmul-fixp.md)
+- [Hosted four-PE group runtime](docs/tileop-usage/group-runtime.md)
 
 ## Validation
 
diff --git a/docs/tileop-usage/group-runtime.md b/docs/tileop-usage/group-runtime.md
new file mode 100644
index 0000000..8e8e2eb
--- /dev/null
+++ b/docs/tileop-usage/group-runtime.md
@@ -0,0 +1,41 @@
+# Hosted four-PE group runtime
+
+The first hosted SMT4 ABI keeps the process runtime on PE0 and uses a small
+worker entry for PE1 through PE3. It is intentionally static-only,
+single-shot, and independent of glibc or musl internals.
+
+## Required symbols
+
+Applications define one worker body:
+
+```cpp
+extern "C" int __linx_group_worker_main(uint32_t peId, void *context);
+```
+
+PE0 calls:
+
+```cpp
+int status = linx_group_run(context);
+```
+
+The linked compiler runtime provides `linx_group_run()` and the non-returning
+`__linx_group_worker_start` entry consumed by gfrun.
+
+## Ownership
+
+- PE0 owns libc startup, TLS, file descriptors, input/output, and process
+  exit.
+- PE1 through PE3 use independent stacks and do not call libc or issue
+  syscalls.
+- `THREAD_ID` selects PE0 through PE3; `BLOCKID` remains the core work ID.
+- The worker body publishes one completion status per PE and then parks until
+  PE0 terminates the process.
+
+## ELF boundary
+
+The first ABI supports static executable and static PIE carriers. A
+`PT_INTERP` image is rejected. A static PIE may contain `PT_DYNAMIC` for
+self-relocation without becoming a dynamically interpreted carrier.
+
+The executable must retain `__linx_group_worker_start` in its symbol table so
+the functional model can assign PE1 through PE3 their initial PC.
diff --git a/include/common/linx_group_runtime.h b/include/common/linx_group_runtime.h
new file mode 100644
index 0000000..e54525d
--- /dev/null
+++ b/include/common/linx_group_runtime.h
@@ -0,0 +1,28 @@
+#ifndef LINX_GROUP_RUNTIME_H
+#define LINX_GROUP_RUNTIME_H
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* One static ELF provides one group worker body. A direct symbol avoids a
+ * function-pointer relocation in the first gfrun ABI. */
+int __linx_group_worker_main(uint32_t pe_id, void *context);
+
+/* Run the ELF's worker body on the fixed four-PE group. PE0 calls this after
+ * hosted libc and input initialization; PE1..PE3 are already parked in the
+ * entry exported below. The first non-zero PE status is returned. */
+int linx_group_run(void *context);
+
+/* Static hosted ELF ABI symbol consumed by gfrun. This entry never enters
+ * libc and never returns. */
+__attribute__((noreturn, used, visibility("default"))) void
+__linx_group_worker_start(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/include/common/pto_tileop.hpp b/include/common/pto_tileop.hpp
index 7ea24f3..892ed55 100644
--- a/include/common/pto_tileop.hpp
+++ b/include/common/pto_tileop.hpp
@@ -4,6 +4,7 @@
 #include "common/pto_tile.hpp"
 #include "common/tileop_api.hpp"
 #include "common/global_iterator.hpp"
+#include "common/linx_group_runtime.h"
 #include "common/tile_tensor_impl.hpp"
 #include "common/debug_utils.hpp"
 
diff --git a/test/linx_group_runtime_api.c b/test/linx_group_runtime_api.c
new file mode 100644
index 0000000..5806a75
--- /dev/null
+++ b/test/linx_group_runtime_api.c
@@ -0,0 +1,7 @@
+#include <common/linx_group_runtime.h>
+
+int __linx_group_worker_main(uint32_t pe_id, void *context) {
+  return context == 0 ? (int)pe_id : 0;
+}
+
+int call_group_runtime_c(void *context) { return linx_group_run(context); }
diff --git a/test/linx_group_runtime_api.cpp b/test/linx_group_runtime_api.cpp
new file mode 100644
index 0000000..5e657a6
--- /dev/null
+++ b/test/linx_group_runtime_api.cpp
@@ -0,0 +1,7 @@
+#include <common/linx_group_runtime.h>
+
+extern "C" int __linx_group_worker_main(uint32_t peId, void *context) {
+  return context == nullptr ? static_cast<int>(peId) : 0;
+}
+
+int call_group_runtime(void *context) { return linx_group_run(context); }