diff --git a/Makefile b/Makefile
index 7c29ab4..4eb552e 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@
 
 CC       ?= cc
 CFLAGS   ?= -O3 -flto -pipe -std=c11 -Wall -D_POSIX_C_SOURCE=200809L -pthread
-SRCS     = main.c server.c jsonapi.c util.c
+SRCS     = main.c server.c jsonapi.c util.c tokenizer.c tokenizer_data.c
 HDRS     = hygate.h
 BINDIR   = bin
 BIN      = $(BINDIR)/hygate
diff --git a/README.md b/README.md
index e005511..69e4798 100644
--- a/README.md
+++ b/README.md
@@ -66,8 +66,30 @@ CORS is enabled for all origins (`Access-Control-Allow-Origin: *`).
 - Upstream calls use Fibonacci-backoff retries (up to `MAX_RETRIES = 5`,
   300 s timeout).
 
+## Token usage counting
+
+Responses include an OpenAI-style `usage` object with `prompt_tokens`,
+`completion_tokens`, and `total_tokens`. These are computed locally by an
+**embedded cl100k_base BPE tokenizer** (vocabulary data in
+`tokenizer_data.c`, logic in `tokenizer.c`) — no upstream token counts are
+available from the Gradio backend.
+
+- `prompt_tokens` sums each message's `content` (or multi-part content
+  parts), `reasoning_content`, and any `tool_calls` function `name` /
+  `arguments`.
+- `completion_tokens` sums the assistant `content`, `reasoning_content`, and
+  any emitted `tool_calls`.
+- `total_tokens = prompt_tokens + completion_tokens`.
+
+cl100k_base is OpenAI's canonical multilingual tokenizer and is used as the
+best available approximation for Hunyuan; the resulting counts are
+deterministic subword counts and may differ slightly from the exact Hunyuan
+vocabulary. No per-message formatting overhead (the `+3`/priming tokens
+OpenAI applies) is added.
+
 ## Security considerations
 
+
 - The server binds all interfaces (`0.0.0.0`) and currently enforces **no
   authentication** — it is an open relay to the configured upstream. Do not
   expose it to untrusted networks without a fronting proxy or auth layer.
diff --git a/hygate.h b/hygate.h
index d11a1ff..f93e6c2 100644
--- a/hygate.h
+++ b/hygate.h
@@ -68,8 +68,20 @@ char *build_gradio_payload(void *req_obj, const char *model_default);
  * frees the result. */
 char *build_completion_response(const char *id, long created, const char *model,
                                 const char *content, const char *reasoning,
-                                tool_call_t *tc, int n_tc);
+                                tool_call_t *tc, int n_tc, int prompt_tokens);
 
+
+/* Token counting (embedded cl100k_base BPE tokenizer). Counts are
+ * deterministic subword counts; the served model (Hunyuan) uses a
+ * different tokenizer, so these are an approximation, not exact. */
+int tok_count(const char *text, int len);
+int tok_count_str(const char *text);
+
+/* Count tokens across an OpenAI request's messages (prompt side). */
+int count_messages_tokens(void *req_obj);
+/* Count tokens of a generated completion (content + reasoning + tool calls). */
+int count_completion_tokens(const char *content, const char *reasoning,
+                            tool_call_t *tc, int n_tc);
 /* Build a streaming tool-call delta JSON array (first emission: full
  * tool call with index). Caller frees the result. */
 char *toolcall_delta_json(tool_call_t *tc, int idx);
diff --git a/jsonapi.c b/jsonapi.c
index 36e2a3e..efc7655 100644
--- a/jsonapi.c
+++ b/jsonapi.c
@@ -4,6 +4,67 @@
 #include <string.h>
 #include <json-c/json.h>
 
+/* forward declaration (defined later in this file) */
+static char *content_to_string(json_object *content);
+
+/* ------------------------------------------------------------------ */
+/* Token counting (embedded cl100k_base BPE)                            */
+/* ------------------------------------------------------------------ */
+int count_messages_tokens(void *req_obj) {
+  json_object *req = (json_object *)req_obj;
+  json_object *messages = NULL;
+  if (!json_object_object_get_ex(req, "messages", &messages) ||
+      json_object_get_type(messages) != json_type_array)
+    return 0;
+  int total = 0;
+  int n = json_object_array_length(messages);
+  for (int i = 0; i < n; i++) {
+    json_object *m = json_object_array_get_idx(messages, i);
+    if (!m) continue;
+    json_object *content = json_object_object_get(m, "content");
+    char *cs = content_to_string(content);
+    total += tok_count_str(cs);
+    free(cs);
+    json_object *rc = NULL;
+    if (json_object_object_get_ex(m, "reasoning_content", &rc) &&
+        json_object_get_type(rc) == json_type_string)
+      total += tok_count_str(json_object_get_string(rc));
+    json_object *tcs = NULL;
+    if (json_object_object_get_ex(m, "tool_calls", &tcs) &&
+        json_object_get_type(tcs) == json_type_array) {
+      int tn = json_object_array_length(tcs);
+      for (int j = 0; j < tn; j++) {
+        json_object *tc = json_object_array_get_idx(tcs, j);
+        if (!tc) continue;
+        json_object *fn = NULL;
+        if (json_object_object_get_ex(tc, "function", &fn) &&
+            json_object_get_type(fn) == json_type_object) {
+          json_object *nm = NULL, *ar = NULL;
+          if (json_object_object_get_ex(fn, "name", &nm) &&
+              json_object_get_type(nm) == json_type_string)
+            total += tok_count_str(json_object_get_string(nm));
+          if (json_object_object_get_ex(fn, "arguments", &ar) &&
+              json_object_get_type(ar) == json_type_string)
+            total += tok_count_str(json_object_get_string(ar));
+        }
+      }
+    }
+  }
+  return total;
+}
+
+int count_completion_tokens(const char *content, const char *reasoning,
+                            tool_call_t *tc, int n_tc) {
+  int total = 0;
+  if (content && content[0]) total += tok_count_str(content);
+  if (reasoning && reasoning[0]) total += tok_count_str(reasoning);
+  for (int i = 0; i < n_tc; i++) {
+    if (tc[i].name && tc[i].name[0]) total += tok_count_str(tc[i].name);
+    if (tc[i].arguments && tc[i].arguments[0]) total += tok_count_str(tc[i].arguments);
+  }
+  return total;
+}
+
 /* Convert an OpenAI "content" field to a flat string. Caller frees. */
 static char *content_to_string(json_object *content) {
   if (!content) return strdup("");
@@ -328,7 +389,7 @@ int parse_gradio_stream(const char *data_json,
 /* ------------------------------------------------------------------ */
 char *build_completion_response(const char *id, long created, const char *model,
                                 const char *content, const char *reasoning,
-                                tool_call_t *tc, int n_tc) {
+                                tool_call_t *tc, int n_tc, int prompt_tokens) {
   bool has_tc = n_tc > 0;
   json_object *root = json_object_new_object();
   json_object_object_add(root, "id", json_object_new_string(id));
@@ -374,10 +435,12 @@ char *build_completion_response(const char *id, long created, const char *model,
   json_object_array_add(choices, choice);
   json_object_object_add(root, "choices", choices);
 
+  int completion_tokens = count_completion_tokens(content, reasoning, tc, n_tc);
+  int total_tokens = prompt_tokens + completion_tokens;
   json_object *usage = json_object_new_object();
-  json_object_object_add(usage, "prompt_tokens", json_object_new_int(0));
-  json_object_object_add(usage, "completion_tokens", json_object_new_int(0));
-  json_object_object_add(usage, "total_tokens", json_object_new_int(0));
+  json_object_object_add(usage, "prompt_tokens", json_object_new_int(prompt_tokens));
+  json_object_object_add(usage, "completion_tokens", json_object_new_int(completion_tokens));
+  json_object_object_add(usage, "total_tokens", json_object_new_int(total_tokens));
   json_object_object_add(root, "usage", usage);
 
   const char *s = json_object_to_json_string(root);
diff --git a/server.c b/server.c
index 3f3fab5..e93616c 100644
--- a/server.c
+++ b/server.c
@@ -30,6 +30,7 @@ typedef struct {
   int tc_state_n;
   int tc_state_cap;
   bool any_toolcall;
+  int include_usage;
   char *final_content;     /* non-streaming accumulation */
   char *final_reasoning;
   tool_call_t *final_tc;
@@ -132,6 +133,31 @@ static void emit_chunk(sse_ctx_t *ctx, const char *role, const char *content,
   json_object_put(root);
 }
 
+static void emit_usage_chunk(sse_ctx_t *ctx, int prompt_tokens, int completion_tokens) {
+  json_object *root = json_object_new_object();
+  json_object_object_add(root, "id", json_object_new_string(ctx->completion_id));
+  json_object_object_add(root, "object", json_object_new_string("chat.completion.chunk"));
+  json_object_object_add(root, "created", json_object_new_int64(ctx->created));
+  json_object_object_add(root, "model", json_object_new_string(ctx->model));
+  json_object *choices = json_object_new_array();
+  json_object_object_add(root, "choices", choices);
+  json_object *usage = json_object_new_object();
+  json_object_object_add(usage, "prompt_tokens", json_object_new_int(prompt_tokens));
+  json_object_object_add(usage, "completion_tokens", json_object_new_int(completion_tokens));
+  json_object_object_add(usage, "total_tokens",
+                         json_object_new_int(prompt_tokens + completion_tokens));
+  json_object_object_add(root, "usage", usage);
+  const char *j = json_object_to_json_string(root);
+  if (j) {
+    size_t need = strlen(j) + 32;
+    char *buf = (char *)malloc(need);
+    int bl = snprintf(buf, need, "data: %s\n\n", j);
+    write_all(ctx->client_fd, buf, (size_t)bl);
+    free(buf);
+  }
+  json_object_put(root);
+}
+
 /* ------------------------------------------------------------------ */
 /* SSE line processing                                                 */
 /* ------------------------------------------------------------------ */
@@ -396,6 +422,18 @@ static void handle_chat(int fd, http_req_t *req, const config_t *cfg) {
   }
 
   char *payload = build_gradio_payload(jreq, model);
+
+  int prompt_tokens = count_messages_tokens(jreq);
+  bool include_usage = false;
+  json_object *so = NULL;
+  if (json_object_object_get_ex(jreq, "stream_options", &so) &&
+      json_object_get_type(so) == json_type_object) {
+    json_object *iu = NULL;
+    if (json_object_object_get_ex(so, "include_usage", &iu) &&
+        json_object_get_type(iu) == json_type_boolean)
+      include_usage = json_object_get_boolean(iu);
+  }
+
   json_object_put(jreq);
   if (!payload) {
     send_simple(fd, 400, "Bad Request", "Invalid request: missing messages");
@@ -457,6 +495,7 @@ static void handle_chat(int fd, http_req_t *req, const config_t *cfg) {
   ctx.client_fd = fd;
   ctx.streaming = stream;
   ctx.model = model;
+  ctx.include_usage = include_usage;
   ctx.created = (long)time(NULL);
   char uuid[37];
   generate_uuid(uuid);
@@ -479,12 +518,19 @@ static void handle_chat(int fd, http_req_t *req, const config_t *cfg) {
 
   if (stream) {
     emit_chunk(&ctx, NULL, NULL, NULL, NULL, ctx.any_toolcall ? "tool_calls" : "stop");
+    if (ctx.include_usage) {
+      int completion_tokens = tok_count_str(ctx.emitted_content.buf);
+      completion_tokens += tok_count_str(ctx.emitted_reasoning.buf);
+      for (int i = 0; i < ctx.tc_state_n; i++)
+        completion_tokens += tok_count_str(ctx.tc_state[i].prev_args);
+      emit_usage_chunk(&ctx, prompt_tokens, completion_tokens);
+    }
     const char *done = "data: [DONE]\n\n";
     write_all(fd, done, strlen(done));
   } else {
     char *resp = build_completion_response(ctx.completion_id, ctx.created, ctx.model,
                                           ctx.final_content, ctx.final_reasoning,
-                                          ctx.final_tc, ctx.final_n_tc);
+                                          ctx.final_tc, ctx.final_n_tc, prompt_tokens);
     if (resp) {
       send_json(fd, resp);
       free(resp);