diff --git a/agent/agent_init.py b/agent/agent_init.py
index 94ab40b876..5e9549e95c 100644
--- a/agent/agent_init.py
+++ b/agent/agent_init.py
@@ -1831,6 +1831,9 @@ def init_agent(
     except Exception:
         agent.show_commentary = True
 
+    # Window (seconds) for the bounded /fast auto|cold modes (agent.fast_mode).
+    agent.fast_auto_seconds = (_agent_cfg.get("agent") or {}).get("fast_auto_seconds", 60)
+
     # LM Studio can either be explicitly preloaded through LM Studio's
     # management API (the historical Hermes behavior) or left to LM Studio's
     # just-in-time / Auto-Evict chat-completions path.  Keep the default
diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 5f7467e291..e352f40ca9 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -34,6 +34,7 @@ from agent.error_classifier import (
     PROVIDER_STREAM_NON_JSON_ERROR_CODE,
 )
 from agent.errors import EmptyStreamError
+from agent.fast_mode import effective_request_overrides
 from agent.turn_context import substitute_api_content
 from agent.gemini_native_adapter import is_native_gemini_base_url
 from agent.model_metadata import is_local_endpoint
@@ -1985,6 +1986,10 @@ def build_api_kwargs(agent, api_messages: list, tools_for_api: list | None = Non
     _wire_reasoning_config = _reasoning_config_for_wire(agent)
     if tools_for_api is None:
         tools_for_api = agent.tools
+    # The one place request_overrides are consumed: static /fast values are
+    # already pinned in agent.request_overrides; auto/cold windows layer the
+    # fast override here, per request, only while the window is open.
+    _request_overrides = effective_request_overrides(agent)
 
     if agent.api_mode == "anthropic_messages":
         _transport = agent._get_transport()
@@ -2004,7 +2009,7 @@ def build_api_kwargs(agent, api_messages: list, tools_for_api: list | None = Non
             preserve_dots=agent._anthropic_preserve_dots(),
             context_length=ctx_len,
             base_url=getattr(agent, "_anthropic_base_url", None),
-            fast_mode=(agent.request_overrides or {}).get("speed") == "fast",
+            fast_mode=_request_overrides.get("speed") == "fast",
             drop_context_1m_beta=bool(getattr(agent, "_oauth_1m_beta_disabled", False)),
         )
         # Nous Portal reads ``tags`` and ``session_id`` as top-level body fields
@@ -2097,7 +2102,7 @@ def build_api_kwargs(agent, api_messages: list, tools_for_api: list | None = Non
             base_url=agent.base_url,
             max_tokens=agent.max_tokens,
             timeout=agent._resolved_api_call_timeout(),
-            request_overrides=agent.request_overrides,
+            request_overrides=_request_overrides,
             provider=getattr(agent, "provider", None),
             is_github_responses=is_github_responses,
             is_codex_backend=is_codex_backend,
@@ -2249,7 +2254,7 @@ def build_api_kwargs(agent, api_messages: list, tools_for_api: list | None = Non
             ephemeral_max_output_tokens=_ephemeral_out,
             max_tokens_param_fn=agent._max_tokens_param,
             reasoning_config=_wire_reasoning_config,
-            request_overrides=agent.request_overrides,
+            request_overrides=_request_overrides,
             session_id=getattr(agent, "session_id", None),
             cache_scope_id=_cache_scope_id,
             provider_profile=_profile,
@@ -2282,7 +2287,7 @@ def build_api_kwargs(agent, api_messages: list, tools_for_api: list | None = Non
         ephemeral_max_output_tokens=_ephemeral_out,
         max_tokens_param_fn=agent._max_tokens_param,
         reasoning_config=_wire_reasoning_config,
-        request_overrides=agent.request_overrides,
+        request_overrides=_request_overrides,
         session_id=getattr(agent, "session_id", None),
         cache_scope_id=_cache_scope_id,
         model_lower=(agent.model or "").lower(),
diff --git a/agent/conversation_loop.py b/agent/conversation_loop.py
index 4c2d5d4949..d404207119 100644
--- a/agent/conversation_loop.py
+++ b/agent/conversation_loop.py
@@ -41,6 +41,7 @@ from agent.conversation_compression import (
 from agent.context_engine import automatic_compaction_status_message
 from agent.display import KawaiiSpinner
 from agent.error_classifier import FailoverReason, classify_api_error
+from agent.fast_mode import begin_turn as begin_fast_mode_turn
 from agent.message_metadata import append_message
 from agent.turn_context import (
     PreflightCompressionTimedOut,
@@ -2042,6 +2043,7 @@ def run_conversation(
     agent._last_compaction_in_place = False
     agent._last_compression_attempt_recorded = False
     agent._last_compression_attempt_in_place = None
+    begin_fast_mode_turn(agent, conversation_history)
 
     # Adopt any ~/.hermes/.env credential/base-url edits made since the last
     # turn — a Settings save updates .env but not this worker's client, which
diff --git a/agent/fast_mode.py b/agent/fast_mode.py
new file mode 100644
index 0000000000..b8121f6295
--- /dev/null
+++ b/agent/fast_mode.py
@@ -0,0 +1,63 @@
+"""Bounded fast-mode windows (``/fast auto`` and ``/fast cold``).
+
+``agent.service_tier`` is ``None`` (normal), ``"priority"`` (static fast),
+``"auto"`` or ``"cold"``. The static value is pinned into
+``agent.request_overrides`` at agent build time; the two bounded modes
+instead open a wall-clock window at each user-turn boundary and layer the
+provider's fast override onto the request kwargs only while it is open:
+
+- ``auto`` — every user turn opens a window of ``agent.fast_auto_seconds``.
+- ``cold`` — only the first turn of a session (no prior history) opens it.
+
+Only per-request params (``service_tier`` / ``speed``) vary between requests;
+the system prompt, tools, and messages are untouched, so the prompt cache is
+preserved across the window boundary.
+"""
+
+from __future__ import annotations
+
+import time
+from typing import Any
+
+BOUNDED_MODES = frozenset({"auto", "cold"})
+DEFAULT_WINDOW_SECONDS = 60
+
+
+def begin_turn(agent: Any, conversation_history: Any) -> None:
+    """Open (or refuse) the fast window at a user-turn boundary."""
+    mode = getattr(agent, "service_tier", None)
+    agent._fast_until = 0.0
+    if mode not in BOUNDED_MODES:
+        return
+    if mode == "cold" and any(
+        isinstance(m, dict) and m.get("role") in ("user", "assistant", "tool")
+        for m in (conversation_history or ())
+    ):
+        return
+    try:
+        window = float(getattr(agent, "fast_auto_seconds", DEFAULT_WINDOW_SECONDS))
+    except (TypeError, ValueError):
+        window = DEFAULT_WINDOW_SECONDS
+    agent._fast_until = time.monotonic() + max(window, 0.0)
+
+
+def effective_request_overrides(agent: Any) -> dict[str, Any]:
+    """``agent.request_overrides`` plus the fast override while the window is open."""
+    overrides = dict(getattr(agent, "request_overrides", None) or {})
+    if getattr(agent, "service_tier", None) not in BOUNDED_MODES:
+        return overrides
+    if time.monotonic() >= getattr(agent, "_fast_until", 0.0):
+        return overrides
+    from hermes_cli.models import resolve_fast_mode_overrides
+
+    base_url = getattr(agent, "base_url", None)
+    if getattr(agent, "api_mode", None) == "anthropic_messages":
+        base_url = getattr(agent, "_anthropic_base_url", None) or base_url
+    fast = resolve_fast_mode_overrides(
+        getattr(agent, "model", None),
+        provider=getattr(agent, "provider", None),
+        base_url=base_url,
+    )
+    if fast:
+        overrides.update(fast)
+    return overrides
diff --git a/cli-config.yaml.example b/cli-config.yaml.example
index 848482adfc..a0954258d9 100644
--- a/cli-config.yaml.example
+++ b/cli-config.yaml.example
@@ -1181,7 +1181,17 @@ agent:
   #   "claude-opus-4.6": "high"           # bare model name also works
   #   "deepseek/deepseek-v4-pro": "xhigh" # dots and dashes are interchangeable
   reasoning_overrides: {}
-  
+
+  # Fast mode (OpenAI Priority Processing / xAI Grok 4.6 / Anthropic Fast Mode
+  # on Opus 4.8+). Premium pricing; only sent to first-party endpoints.
+  #   "" / "normal" - off (default)
+  #   "fast"        - every request
+  #   "auto"        - only the first fast_auto_seconds of every turn
+  #   "cold"        - that window on the first turn of a session only
+  # Also: /fast normal|fast|auto|cold [--global]
+  service_tier: ""
+  fast_auto_seconds: 60
+
   # Custom personalities (use with /personality command).
   # Built-ins (helpful, concise, technical, creative, teacher, kawaii, catgirl,
   # pirate, shakespeare, surfer, noir, uwu, philosopher, hype) are always
diff --git a/cli.py b/cli.py
index 5918f0564a..5797c81318 100644
--- a/cli.py
+++ b/cli.py
@@ -402,12 +402,14 @@ def _parse_reasoning_config(effort) -> dict | None:
 
 
 def _parse_service_tier_config(raw: str) -> str | None:
-    """Parse a persisted service-tier preference into a Responses API value."""
+    """Parse a persisted fast-mode preference: None, "priority", "auto", or "cold"."""
     value = str(raw or "").strip().lower()
     if not value or value in {"normal", "default", "standard", "off", "none"}:
         return None
     if value in {"fast", "priority", "on"}:
         return "priority"
+    if value in {"auto", "cold"}:
+        return value
     logger.warning("Unknown service_tier '%s', ignoring", raw)
     return None
 
diff --git a/gateway/run.py b/gateway/run.py
index 3f2b91d0c7..05c8a59bb8 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -8903,12 +8903,18 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
         # configured extra_body (chat_template_kwargs, etc.) never reached the
         # model on the gateway path -- only /fast service-tier overrides did.
         service_tier = getattr(self, "_service_tier", None)
-        if not service_tier:
+        if service_tier != "priority":
+            # None (normal) or auto/cold — the bounded window is applied per
+            # request by agent.fast_mode, not pinned into request_overrides.
             route["request_overrides"] = base_request_overrides
             return route
 
         try:
-            overrides = resolve_fast_mode_overrides(route["model"])
+            overrides = resolve_fast_mode_overrides(
+                route["model"],
+                provider=runtime["provider"],
+                base_url=runtime["base_url"],
+            )
         except Exception:
             overrides = None
         # Fast-mode overrides (service_tier / speed) are top-level keys and do
@@ -10367,6 +10373,8 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
             return None
         if value in {"fast", "priority", "on"}:
             return "priority"
+        if value in {"auto", "cold"}:
+            return value
         logger.warning("Unknown service_tier '%s', ignoring", raw)
         return None
 
diff --git a/gateway/slash_commands.py b/gateway/slash_commands.py
index 5493e849dc..e8d84e6dcb 100644
--- a/gateway/slash_commands.py
+++ b/gateway/slash_commands.py
@@ -4122,6 +4122,9 @@ class GatewaySlashCommandsMixin:
                 tier = None
                 saved_value = "normal"
                 label = t("gateway.fast.label_normal")
+            elif value in {"auto", "cold"}:
+                tier = saved_value = value
+                label = value.upper()
             else:
                 return t("gateway.fast.unknown_arg", arg=value)
             self._service_tier = tier
@@ -4144,7 +4147,8 @@ class GatewaySlashCommandsMixin:
 
         if not args or args == "status":
             is_fast = self._service_tier == "priority"
-            status = t("gateway.fast.status_fast") if is_fast else t("gateway.fast.status_normal")
+            mode = "fast" if is_fast else (self._service_tier or "normal")
+            status = {"fast": t("gateway.fast.status_fast"), "normal": t("gateway.fast.status_normal")}.get(mode, mode)
 
             async def _on_fast_choice(_chat_id: str, value: str) -> str:
                 return _apply_fast_selection(value, persist=persist_global)
@@ -4162,7 +4166,17 @@ class GatewaySlashCommandsMixin:
                     {
                         "value": "normal",
                         "label": t("gateway.fast.choice_normal"),
-                        "is_current": not is_fast,
+                        "is_current": mode == "normal",
+                    },
+                    {
+                        "value": "auto",
+                        "label": t("gateway.fast.choice_auto"),
+                        "is_current": mode == "auto",
+                    },
+                    {
+                        "value": "cold",
+                        "label": t("gateway.fast.choice_cold"),
+                        "is_current": mode == "cold",
                     },
                 ],
                 on_choice_selected=_on_fast_choice,
diff --git a/hermes_cli/cli_agent_setup_mixin.py b/hermes_cli/cli_agent_setup_mixin.py
index ae5ce2a3e5..46eae97b0d 100644
--- a/hermes_cli/cli_agent_setup_mixin.py
+++ b/hermes_cli/cli_agent_setup_mixin.py
@@ -353,12 +353,18 @@ class CLIAgentSetupMixin:
         }
 
         service_tier = getattr(self, "service_tier", None)
-        if not service_tier:
+        if service_tier != "priority":
+            # None (normal) or auto/cold — the bounded window is applied per
+            # request by agent.fast_mode, not pinned into request_overrides.
             route["request_overrides"] = None
             return route
 
         try:
-            overrides = resolve_fast_mode_overrides(route["model"])
+            overrides = resolve_fast_mode_overrides(
+                route["model"],
+                provider=runtime["provider"],
+                base_url=runtime["base_url"],
+            )
         except Exception:
             overrides = None
         route["request_overrides"] = overrides
diff --git a/hermes_cli/cli_commands_mixin.py b/hermes_cli/cli_commands_mixin.py
index 7fe5737319..b78ff6157c 100644
--- a/hermes_cli/cli_commands_mixin.py
+++ b/hermes_cli/cli_commands_mixin.py
@@ -3989,9 +3989,9 @@ class CLICommandsMixin:
 
         parts = cmd.strip().split(maxsplit=1)
         if len(parts) < 2 or parts[1].strip().lower() == "status":
-            status = "fast" if self.service_tier == "priority" else "normal"
+            status = {"priority": "fast", None: "normal"}.get(self.service_tier, self.service_tier)
             _cprint(f"  {_ACCENT}{feature_name}: {status}{_RST}")
-            _cprint(f"  {_DIM}Usage: /fast [normal|fast|status] [--global]{_RST}")
+            _cprint(f"  {_DIM}Usage: /fast [normal|fast|auto|cold|status] [--global]{_RST}")
             return
 
         arg_tokens = parts[1].strip().lower().split()
@@ -4009,9 +4009,13 @@ class CLICommandsMixin:
             self.service_tier = None
             saved_value = "normal"
             label = "NORMAL"
+        elif arg in {"auto", "cold"}:
+            self.service_tier = arg
+            saved_value = arg
+            label = arg.upper()
         else:
             _cprint(f"  {_DIM}(._.) Unknown argument: {arg}{_RST}")
-            _cprint(f"  {_DIM}Usage: /fast [normal|fast|status] [--global]{_RST}")
+            _cprint(f"  {_DIM}Usage: /fast [normal|fast|auto|cold|status] [--global]{_RST}")
             return
 
         self.agent = None  # Force agent re-init with new service-tier config
diff --git a/hermes_cli/commands.py b/hermes_cli/commands.py
index 23af46886d..f2c2ea7faf 100644
--- a/hermes_cli/commands.py
+++ b/hermes_cli/commands.py
@@ -297,9 +297,9 @@ COMMAND_REGISTRY: list[CommandDef] = [
                args_hint="[level|show|hide|full|clamp] [--global]",
                subcommands=("none", "minimal", "low", "medium", "high", "xhigh", "max", "ultra", "show", "hide", "on", "off", "full", "clamp", "--global"),
                desktop="advanced"),
-    CommandDef("fast", "Toggle fast mode — OpenAI Priority Processing / Anthropic Fast Mode (Normal/Fast)", "Configuration",
-               args_hint="[normal|fast|status] [--global]",
-               subcommands=("normal", "fast", "status", "on", "off", "--global"),
+    CommandDef("fast", "Fast mode — OpenAI Priority Processing / Anthropic Fast Mode (normal/fast/auto/cold)", "Configuration",
+               args_hint="[normal|fast|auto|cold|status] [--global]",
+               subcommands=("normal", "fast", "auto", "cold", "status", "on", "off", "--global"),
                desktop="advanced"),
     CommandDef("skin", "Show or change the display skin/theme", "Configuration",
                cli_only=True, args_hint="[name]", argument_mode="options"),
diff --git a/hermes_cli/config_defaults.py b/hermes_cli/config_defaults.py
index a43ac5b09d..7bce1e561a 100644
--- a/hermes_cli/config_defaults.py
+++ b/hermes_cli/config_defaults.py
@@ -151,7 +151,10 @@ DEFAULT_CONFIG = {
             # leaves the budget untouched.
             "cost_threshold_usd": 0.25,
         },
+        # Fast mode: "" / "normal" (off), "fast" (always), "auto" (first
+        # fast_auto_seconds of every turn), "cold" (first turn of a session only).
         "service_tier": "",
+        "fast_auto_seconds": 60,
         # Tool-use enforcement: injects system prompt guidance that tells the
         # model to actually call tools instead of describing intended actions.
         # Values: "auto" (default — applies to gpt/codex models), true/false
diff --git a/hermes_cli/models.py b/hermes_cli/models.py
index 2c5bc9652d..7968a3f4d9 100644
--- a/hermes_cli/models.py
+++ b/hermes_cli/models.py
@@ -3993,7 +3993,36 @@ def _is_anthropic_fast_model(model_id: Optional[str]) -> bool:
     return any(v in base for v in ("opus-4-8", "opus-4.8", "opus-5"))
 
 
-def resolve_fast_mode_overrides(model_id: Optional[str]) -> dict[str, Any] | None:
+def _fast_mode_route_supported(
+    model_id: Optional[str], provider: Optional[str], base_url: Optional[str]
+) -> bool:
+    """Only the first-party endpoint that bills for fast mode may receive its params.
+
+    OpenRouter, Nous, Copilot, Azure, Bedrock, and custom base_urls either
+    strip ``service_tier``/``speed`` (charging nothing) or 400 on them.
+    """
+    from urllib.parse import urlparse
+
+    from agent.model_metadata import is_grok_46_family
+
+    if _is_anthropic_fast_model(model_id):
+        allowed = {"anthropic": "api.anthropic.com"}
+    elif is_grok_46_family(str(model_id or "")):
+        allowed = {"xai": "api.x.ai"}
+    else:
+        allowed = {"openai": "api.openai.com", "openai-codex": "chatgpt.com"}
+    if provider and normalize_provider(provider) not in allowed:
+        return False
+    host = (urlparse(str(base_url or "")).hostname or "").lower()
+    return not host or host in allowed.values()
+
+
+def resolve_fast_mode_overrides(
+    model_id: Optional[str],
+    *,
+    provider: Optional[str] = None,
+    base_url: Optional[str] = None,
+) -> dict[str, Any] | None:
     """Return request_overrides for fast/priority mode, or None if unsupported.
 
     Returns provider-appropriate overrides:
@@ -4001,12 +4030,21 @@ def resolve_fast_mode_overrides(model_id: Optional[str]) -> dict[str, Any] | Non
     - Anthropic models: ``{"speed": "fast"}`` (Anthropic Fast Mode beta)
     - Grok 4.6: ``{"service_tier": "priority"}`` (xAI Priority Processing)
 
+    When ``provider``/``base_url`` are given the result is also gated on the
+    route (see ``_fast_mode_route_supported``) so proxies never see the
+    params. This is the single fast-mode gate for static ``/fast fast`` and
+    the bounded ``auto``/``cold`` windows in ``agent.fast_mode``.
+
     The overrides are injected into the API request kwargs by
-    ``_build_api_kwargs`` in run_agent.py — each API path handles its own
-    keys (service_tier for OpenAI/Codex, speed for Anthropic Messages).
+    ``build_api_kwargs`` — each API path handles its own keys
+    (service_tier for OpenAI/Codex, speed for Anthropic Messages).
     """
     if not model_supports_fast_mode(model_id):
         return None
+    if (provider or base_url) and not _fast_mode_route_supported(
+        model_id, provider, base_url
+    ):
+        return None
     if _is_anthropic_fast_model(model_id):
         return {"speed": "fast"}
     return {"service_tier": "priority"}
diff --git a/hermes_cli/web_server.py b/hermes_cli/web_server.py
index a2bce1d852..9433f6f16d 100644
--- a/hermes_cli/web_server.py
+++ b/hermes_cli/web_server.py
@@ -1429,8 +1429,8 @@ _SCHEMA_OVERRIDES: Dict[str, Dict[str, Any]] = {
     },
     "agent.service_tier": {
         "type": "select",
-        "description": "API service tier (OpenAI/Anthropic)",
-        "options": ["", "auto", "default", "flex"],
+        "description": "Fast mode: fast = always, auto = first N seconds of each turn, cold = first turn only",
+        "options": ["", "normal", "fast", "auto", "cold"],
     },
     "delegation.reasoning_effort": {
         "type": "select",
diff --git a/locales/af.yaml b/locales/af.yaml
index 21806156ab..363563e9a4 100644
--- a/locales/af.yaml
+++ b/locales/af.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nHuidige modus: `{mode}`\\n\\nKies \\'n opsie:"
     choice_fast:           "fast — Priority Processing aan"
     choice_normal:         "normal — standaardverwerking"
+    choice_auto:           "auto — vinnig vir die eerste sekondes van elke beurt"
+    choice_cold:           "cold — vinnig slegs vir die eerste beurt van 'n sessie"
 
   footer:
     status:                "📎 Looptyd-voetstuk: **{state}**\nVelde: `{fields}`\nPlatform: `{platform}`"
diff --git a/locales/ar.yaml b/locales/ar.yaml
index 1f68628a3b..abdc371ead 100644
--- a/locales/ar.yaml
+++ b/locales/ar.yaml
@@ -160,6 +160,8 @@ gateway:
     picker_title:          "⚡ **المعالجة ذات الأولوية**\n\nالوضع الحالي: `{mode}`\n\nاختر خيارًا:"
     choice_fast:           "fast — المعالجة ذات الأولوية مُفعّلة"
     choice_normal:         "normal — المعالجة القياسية"
+    choice_auto:           "auto — سريع في الثواني الأولى من كل دور"
+    choice_cold:           "cold — سريع في الدور الأول من الجلسة فقط"
 
   footer:
     status:                "📎 تذييل التشغيل: **{state}**\nالحقول: `{fields}`\nالمنصّة: `{platform}`"
diff --git a/locales/de.yaml b/locales/de.yaml
index bc00bfe32f..d6e1528088 100644
--- a/locales/de.yaml
+++ b/locales/de.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nAktueller Modus: `{mode}`\\n\\nOption wählen:"
     choice_fast:           "fast — Priority Processing an"
     choice_normal:         "normal — Standardverarbeitung"
+    choice_auto:           "auto — schnell in den ersten Sekunden jedes Zugs"
+    choice_cold:           "cold — schnell nur im ersten Zug einer Sitzung"
 
   footer:
     status:                "📎 Laufzeit-Fußzeile: **{state}**\nFelder: `{fields}`\nPlattform: `{platform}`"
diff --git a/locales/en.yaml b/locales/en.yaml
index 2adac023f2..9b06ae1e96 100644
--- a/locales/en.yaml
+++ b/locales/en.yaml
@@ -141,8 +141,8 @@ gateway:
 
   fast:
     not_supported:         "⚡ /fast is only available for OpenAI models that support Priority Processing."
-    status:                "⚡ Priority Processing\n\nCurrent mode: `{mode}`\n\n_Usage:_ `/fast <normal|fast|status>`"
-    unknown_arg:           "⚠️ Unknown argument: `{arg}`\n\n**Valid options:** normal, fast, status"
+    status:                "⚡ Priority Processing\n\nCurrent mode: `{mode}`\n\n_Usage:_ `/fast <normal|fast|auto|cold|status>`"
+    unknown_arg:           "⚠️ Unknown argument: `{arg}`\n\n**Valid options:** normal, fast, auto, cold, status"
     saved:                 "⚡ ✓ Priority Processing: **{label}** (saved to config)\n_(takes effect on next message)_"
     session_only:          "⚡ ✓ Priority Processing: **{label}** (this session only)"
     label_fast:            "FAST"
@@ -152,6 +152,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\n\nCurrent mode: `{mode}`\n\nPick an option:"
     choice_fast:           "fast — Priority Processing on"
     choice_normal:         "normal — standard processing"
+    choice_auto:           "auto — fast for the first seconds of every turn"
+    choice_cold:           "cold — fast for the first turn of a session only"
 
   footer:
     status:                "📎 Runtime footer: **{state}**\nFields: `{fields}`\nPlatform: `{platform}`"
diff --git a/locales/es.yaml b/locales/es.yaml
index 6b06a52afb..06cd2e9e23 100644
--- a/locales/es.yaml
+++ b/locales/es.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nModo actual: `{mode}`\\n\\nElige una opción:"
     choice_fast:           "fast — Priority Processing activado"
     choice_normal:         "normal — procesamiento estándar"
+    choice_auto:           "auto — rápido en los primeros segundos de cada turno"
+    choice_cold:           "cold — rápido solo en el primer turno de una sesión"
 
   footer:
     status:                "📎 Pie de ejecución: **{state}**\nCampos: `{fields}`\nPlataforma: `{platform}`"
diff --git a/locales/fr.yaml b/locales/fr.yaml
index 4ce9760969..4f1faa6cbf 100644
--- a/locales/fr.yaml
+++ b/locales/fr.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nMode actuel : `{mode}`\\n\\nChoisissez une option :"
     choice_fast:           "fast — Priority Processing activé"
     choice_normal:         "normal — traitement standard"
+    choice_auto:           "auto — rapide pendant les premières secondes de chaque tour"
+    choice_cold:           "cold — rapide uniquement au premier tour d'une session"
 
   footer:
     status:                "📎 Pied de page d'exécution : **{state}**\nChamps : `{fields}`\nPlateforme : `{platform}`"
diff --git a/locales/ga.yaml b/locales/ga.yaml
index 92ef5363ea..843dc5a1c2 100644
--- a/locales/ga.yaml
+++ b/locales/ga.yaml
@@ -141,6 +141,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nMód reatha: `{mode}`\\n\\nRoghnaigh rogha:"
     choice_fast:           "fast — Priority Processing ar siúl"
     choice_normal:         "normal — gnáthphróiseáil"
+    choice_auto:           "auto — tapa do na chéad soicindí de gach seal"
+    choice_cold:           "cold — tapa don chéad seal de sheisiún amháin"
 
   footer:
     status:                "📎 Buntásc rite: **{state}**\nRéimsí: `{fields}`\nArdán: `{platform}`"
diff --git a/locales/hu.yaml b/locales/hu.yaml
index b8feb1b994..d134d4372f 100644
--- a/locales/hu.yaml
+++ b/locales/hu.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nJelenlegi mód: `{mode}`\\n\\nVálassz egy opciót:"
     choice_fast:           "fast — Priority Processing bekapcsolva"
     choice_normal:         "normal — normál feldolgozás"
+    choice_auto:           "auto — gyors minden kör első másodperceiben"
+    choice_cold:           "cold — gyors csak a munkamenet első körében"
 
   footer:
     status:                "📎 Futási idejű lábléc: **{state}**\nMezők: `{fields}`\nPlatform: `{platform}`"
diff --git a/locales/it.yaml b/locales/it.yaml
index 758be5d8a7..a3480541bc 100644
--- a/locales/it.yaml
+++ b/locales/it.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nModalità attuale: `{mode}`\\n\\nScegli un\\'opzione:"
     choice_fast:           "fast — Priority Processing attivo"
     choice_normal:         "normal — elaborazione standard"
+    choice_auto:           "auto — veloce nei primi secondi di ogni turno"
+    choice_cold:           "cold — veloce solo nel primo turno di una sessione"
 
   footer:
     status:                "📎 Footer di runtime: **{state}**\nCampi: `{fields}`\nPiattaforma: `{platform}`"
diff --git a/locales/ja.yaml b/locales/ja.yaml
index 28b41682aa..b691daf93d 100644
--- a/locales/ja.yaml
+++ b/locales/ja.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\n現在のモード: `{mode}`\\n\\nオプションを選択:"
     choice_fast:           "fast — Priority Processing オン"
     choice_normal:         "normal — 標準処理"
+    choice_auto:           "auto — 各ターンの最初の数秒間だけ高速"
+    choice_cold:           "cold — セッションの最初のターンのみ高速"
 
   footer:
     status:                "📎 ランタイムフッター: **{state}**\nフィールド: `{fields}`\nプラットフォーム: `{platform}`"
diff --git a/locales/ko.yaml b/locales/ko.yaml
index ecf58bbc68..f7f4f25a06 100644
--- a/locales/ko.yaml
+++ b/locales/ko.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\n현재 모드: `{mode}`\\n\\n옵션을 선택하세요:"
     choice_fast:           "fast — Priority Processing 켜기"
     choice_normal:         "normal — 표준 처리"
+    choice_auto:           "auto — 매 턴의 처음 몇 초 동안 빠름"
+    choice_cold:           "cold — 세션의 첫 턴에만 빠름"
 
   footer:
     status:                "📎 런타임 푸터: **{state}**\n필드: `{fields}`\n플랫폼: `{platform}`"
diff --git a/locales/pt.yaml b/locales/pt.yaml
index 1ac1fd4b00..f18100340e 100644
--- a/locales/pt.yaml
+++ b/locales/pt.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nModo atual: `{mode}`\\n\\nEscolha uma opção:"
     choice_fast:           "fast — Priority Processing ativado"
     choice_normal:         "normal — processamento padrão"
+    choice_auto:           "auto — rápido nos primeiros segundos de cada turno"
+    choice_cold:           "cold — rápido apenas no primeiro turno de uma sessão"
 
   footer:
     status:                "📎 Rodapé de execução: **{state}**\nCampos: `{fields}`\nPlataforma: `{platform}`"
diff --git a/locales/ru.yaml b/locales/ru.yaml
index 51c892e02e..7fd2c285f2 100644
--- a/locales/ru.yaml
+++ b/locales/ru.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nТекущий режим: `{mode}`\\n\\nВыберите вариант:"
     choice_fast:           "fast — Priority Processing включён"
     choice_normal:         "normal — стандартная обработка"
+    choice_auto:           "auto — быстро в первые секунды каждого хода"
+    choice_cold:           "cold — быстро только на первом ходе сессии"
 
   footer:
     status:                "📎 Нижний колонтитул среды выполнения: **{state}**\nПоля: `{fields}`\nПлатформа: `{platform}`"
diff --git a/locales/tr.yaml b/locales/tr.yaml
index a88b1d0586..7af791fb74 100644
--- a/locales/tr.yaml
+++ b/locales/tr.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nMevcut mod: `{mode}`\\n\\nBir seçenek seçin:"
     choice_fast:           "fast — Priority Processing açık"
     choice_normal:         "normal — standart işleme"
+    choice_auto:           "auto — her turun ilk saniyelerinde hızlı"
+    choice_cold:           "cold — yalnızca oturumun ilk turunda hızlı"
 
   footer:
     status:                "📎 Çalışma zamanı altbilgisi: **{state}**\nAlanlar: `{fields}`\nPlatform: `{platform}`"
diff --git a/locales/uk.yaml b/locales/uk.yaml
index 730a052cd5..5e63f0bdad 100644
--- a/locales/uk.yaml
+++ b/locales/uk.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\nПоточний режим: `{mode}`\\n\\nОберіть варіант:"
     choice_fast:           "fast — Priority Processing увімкнено"
     choice_normal:         "normal — стандартна обробка"
+    choice_auto:           "auto — швидко в перші секунди кожного ходу"
+    choice_cold:           "cold — швидко лише на першому ході сесії"
 
   footer:
     status:                "📎 Нижній колонтитул середовища: **{state}**\nПоля: `{fields}`\nПлатформа: `{platform}`"
diff --git a/locales/zh-hant.yaml b/locales/zh-hant.yaml
index 9468fbba1c..b9091c2aa2 100644
--- a/locales/zh-hant.yaml
+++ b/locales/zh-hant.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **Priority Processing**\\n\\n目前模式：`{mode}`\\n\\n請選擇："
     choice_fast:           "fast — 開啟 Priority Processing"
     choice_normal:         "normal — 標準處理"
+    choice_auto:           "auto — 每輪的前幾秒快速"
+    choice_cold:           "cold — 僅會話的第一輪快速"
 
   footer:
     status:                "📎 執行階段頁尾：**{state}**\n欄位：`{fields}`\n平台：`{platform}`"
diff --git a/locales/zh.yaml b/locales/zh.yaml
index f659de9a24..dde25d0e82 100644
--- a/locales/zh.yaml
+++ b/locales/zh.yaml
@@ -137,6 +137,8 @@ gateway:
     picker_title:          "⚡ **优先处理**\\n\\n当前模式：`{mode}`\\n\\n请选择："
     choice_fast:           "fast — 开启优先处理"
     choice_normal:         "normal — 标准处理"
+    choice_auto:           "auto — 每轮的前几秒快速"
+    choice_cold:           "cold — 仅会话的第一轮快速"
 
   footer:
     status:                "📎 运行时页脚：**{state}**\n字段：`{fields}`\n平台：`{platform}`"
diff --git a/tests/agent/test_fast_mode_auto.py b/tests/agent/test_fast_mode_auto.py
new file mode 100644
index 0000000000..a9af81a8df
--- /dev/null
+++ b/tests/agent/test_fast_mode_auto.py
@@ -0,0 +1,143 @@
+"""Bounded /fast auto|cold windows and the shared route-aware gate."""
+
+from types import SimpleNamespace
+
+from agent import fast_mode
+
+
+def _agent(**kw):
+    base = dict(
+        service_tier="auto",
+        model="gpt-5.4",
+        provider="openai",
+        base_url="https://api.openai.com/v1",
+        api_mode="chat_completions",
+        request_overrides={"extra_body": {"keep": 1}},
+        fast_auto_seconds=60,
+    )
+    base.update(kw)
+    return SimpleNamespace(**base)
+
+
+def test_bounded_fast_window_policy(monkeypatch):
+    clock = [1000.0]
+    monkeypatch.setattr(fast_mode.time, "monotonic", lambda: clock[0])
+
+    # auto: window open -> fast override layered over existing overrides
+    agent = _agent()
+    fast_mode.begin_turn(agent, conversation_history=[])
+    assert fast_mode.effective_request_overrides(agent) == {
+        "extra_body": {"keep": 1},
+        "service_tier": "priority",
+    }
+    assert agent.request_overrides == {"extra_body": {"keep": 1}}  # never mutated
+
+    # window expired -> override absent
+    clock[0] += 61
+    assert fast_mode.effective_request_overrides(agent) == {"extra_body": {"keep": 1}}
+
+    # auto re-opens on the next turn
+    fast_mode.begin_turn(agent, conversation_history=[{"role": "user", "content": "x"}])
+    assert "service_tier" in fast_mode.effective_request_overrides(agent)
+
+    # cold: prior history -> no window at all
+    cold = _agent(service_tier="cold")
+    fast_mode.begin_turn(cold, conversation_history=[{"role": "user", "content": "x"}])
+    assert "service_tier" not in fast_mode.effective_request_overrides(cold)
+    fast_mode.begin_turn(cold, conversation_history=None)
+    assert fast_mode.effective_request_overrides(cold)["service_tier"] == "priority"
+
+    # Anthropic route uses the speed param
+    anth = _agent(
+        service_tier="auto",
+        model="claude-opus-5",
+        provider="anthropic",
+        base_url="https://api.anthropic.com",
+        api_mode="anthropic_messages",
+    )
+    fast_mode.begin_turn(anth, conversation_history=[])
+    assert fast_mode.effective_request_overrides(anth)["speed"] == "fast"
+
+    # unsupported routes never get fast params, in auto or static mode
+    from hermes_cli.models import resolve_fast_mode_overrides
+
+    for provider, base_url in (
+        ("openrouter", "https://openrouter.ai/api/v1"),
+        ("nous", "https://inference-api.nousresearch.com/v1"),
+        ("copilot", "https://api.githubcopilot.com"),
+        ("azure", "https://foo.openai.azure.com"),
+        ("custom", "http://10.0.0.1:8000/v1"),
+        ("openai", "https://proxy.example.com/v1"),
+    ):
+        proxied = _agent(provider=provider, base_url=base_url)
+        fast_mode.begin_turn(proxied, conversation_history=[])
+        assert "service_tier" not in fast_mode.effective_request_overrides(proxied), provider
+        assert resolve_fast_mode_overrides("gpt-5.4", provider=provider, base_url=base_url) is None
+    assert resolve_fast_mode_overrides(
+        "claude-opus-5", provider="bedrock", base_url="https://bedrock-runtime.us-east-1.amazonaws.com"
+    ) is None
+    # first-party routes (and the legacy model-only call) still resolve
+    assert resolve_fast_mode_overrides("gpt-5.4", provider="openai-codex", base_url="https://chatgpt.com/backend-api/codex")
+    assert resolve_fast_mode_overrides("grok-4.6", provider="xai", base_url="https://api.x.ai/v1")
+    assert resolve_fast_mode_overrides("gpt-5.4") == {"service_tier": "priority"}
+
+    # normal / static modes are untouched by the window logic
+    static = _agent(service_tier="priority", request_overrides={"service_tier": "priority"})
+    fast_mode.begin_turn(static, conversation_history=[])
+    assert fast_mode.effective_request_overrides(static) == {"service_tier": "priority"}
+    off = _agent(service_tier=None)
+    fast_mode.begin_turn(off, conversation_history=[])
+    assert fast_mode.effective_request_overrides(off) == {"extra_body": {"keep": 1}}
+
+
+def test_fast_auto_and_cold_parse_and_slash_command(monkeypatch):
+    import hermes_cli.config as config_mod
+
+    if not hasattr(config_mod, "save_env_value_secure"):
+        config_mod.save_env_value_secure = lambda key, value: {"success": True}
+    import cli as cli_mod
+    from gateway.run import GatewayRunner
+    from hermes_cli.commands import COMMAND_REGISTRY
+    from hermes_cli.config import DEFAULT_CONFIG
+
+    # config parsing: CLI, gateway, TUI all accept auto/cold; default stays off
+    for raw, expected in (("auto", "auto"), ("COLD", "cold"), ("fast", "priority"), ("", None), ("bogus", None)):
+        assert cli_mod._parse_service_tier_config(raw) == expected
+        monkeypatch.setattr(
+            "gateway.run._load_gateway_runtime_config", lambda: {"agent": {"service_tier": raw}}
+        )
+        assert GatewayRunner._load_service_tier() == expected
+    assert DEFAULT_CONFIG["agent"]["service_tier"] == ""
+    assert DEFAULT_CONFIG["agent"]["fast_auto_seconds"] == 60
+
+    # /fast auto — session-scoped, agent rebuilt, status reports the mode
+    fast_cmd = next(c for c in COMMAND_REGISTRY if c.name == "fast")
+    assert {"auto", "cold"} <= set(fast_cmd.subcommands)
+    printed = []
+    monkeypatch.setattr(cli_mod, "_cprint", lambda *a, **k: printed.append(" ".join(map(str, a))))
+    monkeypatch.setattr(cli_mod, "save_config_value", lambda *a, **k: (_ for _ in ()).throw(AssertionError("no config write")))
+    stub = SimpleNamespace(
+        service_tier=None, model="gpt-5.4", agent=object(), _fast_command_available=lambda: True
+    )
+    cli_mod.HermesCLI._handle_fast_command(stub, "/fast auto")
+    assert stub.service_tier == "auto"
+    assert stub.agent is None
+    cli_mod.HermesCLI._handle_fast_command(stub, "/fast status")
+    assert any("auto" in line for line in printed)
+    cli_mod.HermesCLI._handle_fast_command(stub, "/fast cold")
+    assert stub.service_tier == "cold"
+
+    # auto/cold do NOT pin a static override into the turn route
+    route_stub = SimpleNamespace(
+        model="gpt-5.4", api_key="k", base_url="https://api.openai.com/v1", provider="openai",
+        api_mode="chat_completions", acp_command=None, acp_args=[], _credential_pool=None,
+        service_tier="auto",
+    )
+    assert cli_mod.HermesCLI._resolve_turn_agent_config(route_stub, "hi")["request_overrides"] is None
+    route_stub.service_tier = "priority"
+    assert cli_mod.HermesCLI._resolve_turn_agent_config(route_stub, "hi")["request_overrides"] == {
+        "service_tier": "priority"
+    }
+    route_stub.base_url = "https://openrouter.ai/api/v1"
+    route_stub.provider = "openrouter"
+    assert cli_mod.HermesCLI._resolve_turn_agent_config(route_stub, "hi")["request_overrides"] is None
diff --git a/tests/cli/test_fast_command.py b/tests/cli/test_fast_command.py
index 23170bc300..203dfe329d 100644
--- a/tests/cli/test_fast_command.py
+++ b/tests/cli/test_fast_command.py
@@ -159,8 +159,8 @@ class TestFastModeRouting(unittest.TestCase):
         stub = SimpleNamespace(
             model="gpt-5.4",
             api_key="primary-key",
-            base_url="https://openrouter.ai/api/v1",
-            provider="openrouter",
+            base_url="https://api.openai.com/v1",
+            provider="openai",
             api_mode="chat_completions",
             acp_command=None,
             acp_args=[],
@@ -171,11 +171,16 @@ class TestFastModeRouting(unittest.TestCase):
         route = cli_mod.HermesCLI._resolve_turn_agent_config(stub, "hi")
 
         # Provider should NOT have changed
-        assert route["runtime"]["provider"] == "openrouter"
+        assert route["runtime"]["provider"] == "openai"
         assert route["runtime"]["api_mode"] == "chat_completions"
         # But request_overrides should be set
         assert route["request_overrides"] == {"service_tier": "priority"}
 
+        # Proxied routes (OpenRouter etc.) strip/400 on the param — never sent.
+        stub.base_url = "https://openrouter.ai/api/v1"
+        stub.provider = "openrouter"
+        assert cli_mod.HermesCLI._resolve_turn_agent_config(stub, "hi")["request_overrides"] is None
+
     def test_turn_route_keeps_primary_runtime_when_model_has_no_fast_backend(self):
         cli_mod = _import_cli()
         stub = SimpleNamespace(
diff --git a/tests/gateway/test_choice_picker.py b/tests/gateway/test_choice_picker.py
index a2c9a52961..c8e6712ec0 100644
--- a/tests/gateway/test_choice_picker.py
+++ b/tests/gateway/test_choice_picker.py
@@ -126,7 +126,7 @@ class TestFastChoicePicker:
 
         assert result is None
         values = [c["value"] for c in adapter.calls[0]["choices"]]
-        assert values == ["fast", "normal"]
+        assert values == ["fast", "normal", "auto", "cold"]
 
     @pytest.mark.asyncio
     async def test_fast_picker_selection_is_session_scoped(self, tmp_path, monkeypatch):
diff --git a/tests/gateway/test_fast_command.py b/tests/gateway/test_fast_command.py
index c714b76e84..b8792ecce4 100644
--- a/tests/gateway/test_fast_command.py
+++ b/tests/gateway/test_fast_command.py
@@ -109,8 +109,8 @@ def test_turn_route_injects_priority_processing_without_changing_runtime():
     runner._service_tier = "priority"
     runtime_kwargs = {
         "api_key": "***",
-        "base_url": "https://openrouter.ai/api/v1",
-        "provider": "openrouter",
+        "base_url": "https://api.openai.com/v1",
+        "provider": "openai",
         "api_mode": "chat_completions",
         "command": None,
         "args": [],
@@ -119,10 +119,15 @@ def test_turn_route_injects_priority_processing_without_changing_runtime():
 
     route = gateway_run.GatewayRunner._resolve_turn_agent_config(runner, "hi", "gpt-5.4", runtime_kwargs)
 
-    assert route["runtime"]["provider"] == "openrouter"
+    assert route["runtime"]["provider"] == "openai"
     assert route["runtime"]["api_mode"] == "chat_completions"
     assert route["request_overrides"] == {"service_tier": "priority"}
 
+    # Proxied routes never receive the param (OpenRouter strips it / others 400).
+    runtime_kwargs.update(base_url="https://openrouter.ai/api/v1", provider="openrouter")
+    route = gateway_run.GatewayRunner._resolve_turn_agent_config(runner, "hi", "gpt-5.4", runtime_kwargs)
+    assert route["request_overrides"] == {}
+
 
 @pytest.mark.asyncio
 async def test_handle_fast_command_global_flag_persists_config(monkeypatch, tmp_path):
diff --git a/tests/gateway/test_turn_request_overrides.py b/tests/gateway/test_turn_request_overrides.py
index c985125176..bd5da602d8 100644
--- a/tests/gateway/test_turn_request_overrides.py
+++ b/tests/gateway/test_turn_request_overrides.py
@@ -53,7 +53,7 @@ def test_provider_request_overrides_merged_under_fast_mode(monkeypatch):
     """/fast active: provider extra_body AND the service-tier marker both survive."""
     monkeypatch.setattr(
         "hermes_cli.models.resolve_fast_mode_overrides",
-        lambda model_id: {"service_tier": "priority"},
+        lambda model_id, **_route: {"service_tier": "priority"},
     )
     runner = _runner(service_tier="priority")
     rk = _runtime_kwargs(request_overrides=PROVIDER_OVERRIDES)
diff --git a/tests/test_tui_gateway_server.py b/tests/test_tui_gateway_server.py
index fcb059da82..724efd7d45 100644
--- a/tests/test_tui_gateway_server.py
+++ b/tests/test_tui_gateway_server.py
@@ -8504,7 +8504,7 @@ def test_config_set_fast_updates_live_agent_session_scoped(monkeypatch):
     monkeypatch.setattr(server, "_emit", lambda *args: emits.append(args))
     monkeypatch.setattr(
         "hermes_cli.models.resolve_fast_mode_overrides",
-        lambda _model_id: {"service_tier": "priority"},
+        lambda _model_id, **_route: {"service_tier": "priority"},
     )
 
     try:
@@ -8583,7 +8583,7 @@ def test_config_set_fast_rejects_unsupported_model(monkeypatch):
     )
     monkeypatch.setattr(
         "hermes_cli.models.resolve_fast_mode_overrides",
-        lambda _model_id: None,
+        lambda _model_id, **_route: None,
     )
 
     try:
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 9a519659eb..b50ee9d265 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -6113,6 +6113,8 @@ def _load_service_tier() -> str | None:
         return None
     if raw in {"fast", "priority", "on"}:
         return "priority"
+    if raw in {"auto", "cold"}:
+        return raw
     return None
 
 
@@ -14644,19 +14646,20 @@ def _(rid, params: dict) -> dict:
         raw = str(value or "").strip().lower()
         agent = session.get("agent") if session else None
         if agent is not None:
-            current_fast = getattr(agent, "service_tier", None) == "priority"
+            current_tier = getattr(agent, "service_tier", None)
         elif session is not None and session.get("create_service_tier_override") is not None:
             # Pre-build session with a pinned tier (desktop draft pick or an
             # earlier session-scoped toggle) — report/toggle from the pin, not
             # the global default.
-            current_fast = session["create_service_tier_override"] == "priority"
+            current_tier = session["create_service_tier_override"] or None
         else:
-            current_fast = _load_service_tier() == "priority"
+            current_tier = _load_service_tier()
+        current_fast = current_tier == "priority"
 
         if raw in {"status"}:
             return _ok(
                 rid,
-                {"key": key, "value": "fast" if current_fast else "normal"},
+                {"key": key, "value": {"priority": "fast", None: "normal"}.get(current_tier, current_tier)},
             )
 
         if raw in {"", "toggle"}:
@@ -14665,6 +14668,8 @@ def _(rid, params: dict) -> dict:
             nv = "fast"
         elif raw in {"normal", "off"}:
             nv = "normal"
+        elif raw in {"auto", "cold"}:
+            nv = raw
         else:
             return _err(rid, 4002, f"unknown fast mode: {value}")
 
@@ -14690,7 +14695,11 @@ def _(rid, params: dict) -> dict:
                     4002,
                     "fast mode is not available without a selected model",
                 )
-            overrides = resolve_fast_mode_overrides(target_model)
+            overrides = resolve_fast_mode_overrides(
+                target_model,
+                provider=getattr(agent, "provider", None),
+                base_url=getattr(agent, "base_url", None),
+            )
             if overrides is None:
                 return _err(
                     rid,
@@ -14707,13 +14716,11 @@ def _(rid, params: dict) -> dict:
             # build ("switch one session, switches everywhere"). Pin the
             # create override so lazily-built sessions and rebuilds (/new,
             # deferred resume) keep the choice; "" pins normal explicitly.
-            session["create_service_tier_override"] = (
-                "priority" if nv == "fast" else ""
-            )
+            session["create_service_tier_override"] = {"fast": "priority", "normal": ""}.get(nv, nv)
         else:
             _write_config_key("agent.service_tier", nv)
         if agent is not None:
-            agent.service_tier = "priority" if nv == "fast" else None
+            agent.service_tier = {"fast": "priority", "normal": None}.get(nv, nv)
             current_overrides = dict(getattr(agent, "request_overrides", {}) or {})
             current_overrides.pop("service_tier", None)
             current_overrides.pop("speed", None)
@@ -16897,6 +16904,8 @@ def _mirror_slash_side_effects(sid: str, session: dict, command: str) -> str:
                 agent.service_tier = "priority"
             elif mode in {"normal", "off"}:
                 agent.service_tier = None
+            elif mode in {"auto", "cold"}:
+                agent.service_tier = mode
             _emit("session.info", sid, _session_info(agent, session))
         elif name == "reload-mcp" and agent and hasattr(agent, "reload_mcp_tools"):
             agent.reload_mcp_tools()
diff --git a/website/docs/reference/slash-commands.md b/website/docs/reference/slash-commands.md
index 41dd223b7f..f7a281d44f 100644
--- a/website/docs/reference/slash-commands.md
+++ b/website/docs/reference/slash-commands.md
@@ -81,7 +81,7 @@ Type `/` in the CLI to open the autocomplete menu. Built-in commands are case-in
 | `/personality` | Set a predefined personality. `/personality none` (or `default` / `neutral`) clears the overlay and returns to base behavior. |
 | `/verbose` | Cycle tool progress display: off → new → all → verbose. Can be [enabled for messaging](#notes) via config. |
 | `/focus [on\|off\|status]` | Toggle **focus view** — a display-only reduced-output mode showing just your prompt and the final response. Composes with `/verbose`: turning it on snaps tool progress to `off` and remembers your previous mode, and `/focus off` restores it. Each turn ends with a dim recovery line (`⋯ 7 tool lines hidden · /focus off to show`) and a persistent `◉ focus` badge sits in the status bar so you always know you're in the reduced view. Nothing is sent differently to the model — detail is hidden, never discarded. |
-| `/fast [normal\|fast\|status]` | Toggle fast mode — OpenAI Priority Processing / Anthropic Fast Mode. Options: `normal`, `fast`, `status`. |
+| `/fast [normal\|fast\|auto\|cold\|status]` | Fast mode — OpenAI Priority Processing / Anthropic Fast Mode. `fast` = every request; `auto` = only requests in the first `agent.fast_auto_seconds` (default 60s) of each turn; `cold` = that same window on the first turn of a session only. Default `normal` (off). See [Fast mode](../user-guide/configuration.md#fast-mode). |
 | `/reasoning [level\|show\|hide\|full\|clamp] [--global]` | Manage reasoning effort and display. Levels include `none` / `minimal` / `low` / `medium` / `high` / `xhigh` / `max` / `ultra`. `show` / `hide` (or `on` / `off`) toggle reasoning display; `full` and `clamp` adjust how reasoning is shown. `--global` persists effort to config. |
 | `/skin` | Show or change the display skin/theme |
 | `/export [profile] [-o out.tar.gz]` | **CLI only.** Pack a profile into a shareable `.tar.gz` — skills, memory, persona, crons, plugins, settings, and (from the desktop) themes and layout. Credentials (`auth.json`, `.env`) are stripped. Defaults to the active profile and `<name>.tar.gz` in the current directory. Same archive as `hermes profile export`; for a versioned, updatable share use a [profile distribution](../user-guide/profile-distributions.md) instead. |
@@ -246,7 +246,7 @@ The messaging gateway supports the following built-in commands inside Telegram,
 | `/model [provider:model]` | Show or change the model. Supports provider switches (`/model zai:glm-5`), custom endpoints (`/model custom:model`), named custom providers (`/model custom:local:qwen`), auto-detect (`/model custom`), and user-defined aliases (`/model fav`, `/model grok` — see [Custom model aliases](#custom-model-aliases)). Use `--global` to persist the change to config.yaml. **Note:** `/model` can only switch between already-configured providers. To add a new provider or set up API keys, use `hermes model` from your terminal (outside the chat session). **Cost note:** a mid-session model switch resets the prompt cache (the cache key includes the model), so the next message re-reads the whole conversation at full input price. |
 | `/codex-runtime [auto\|codex_app_server\|on\|off]` | Toggle the optional [Codex app-server runtime](../user-guide/features/codex-app-server-runtime). Persists to `model.openai_runtime` in config.yaml and evicts the cached agent so the next message picks up the new runtime. Effective on next session. |
 | `/personality [name]` | Set a personality overlay for the session. `/personality none` (or `default` / `neutral`) clears it. |
-| `/fast [normal\|fast\|status]` | Toggle fast mode — OpenAI Priority Processing / Anthropic Fast Mode. |
+| `/fast [normal\|fast\|auto\|cold\|status]` | Fast mode — OpenAI Priority Processing / Anthropic Fast Mode. `auto`/`cold` open a bounded fast window per turn / per session. |
 | `/retry` | Retry the last message. |
 | `/undo` | Remove the last exchange. |
 | `/sethome` (alias: `/set-home`) | Mark the current chat as the platform home channel for deliveries. |
diff --git a/website/docs/user-guide/configuration.md b/website/docs/user-guide/configuration.md
index 95c0a1c030..2e2778760d 100644
--- a/website/docs/user-guide/configuration.md
+++ b/website/docs/user-guide/configuration.md
@@ -1701,6 +1701,27 @@ There is no `hermes config set` support for `reasoning_overrides` keys — edit
 
 The override applies automatically everywhere: CLI startup, messaging gateway, Desktop/TUI, cron jobs, `/model` mid-session switches, and fallback model activation.
 
+## Fast Mode
+
+Fast mode asks the provider for faster output at a premium price: OpenAI [Priority Processing](https://openai.com/api-priority-processing/) (`service_tier: priority`), xAI Priority Processing on Grok 4.6, and Anthropic [Fast Mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) (`speed: fast`, Opus 4.8 / Opus 5 only). It is **off by default**.
+
+```yaml
+agent:
+  service_tier: ""          # "" / normal | fast | auto | cold
+  fast_auto_seconds: 60     # window for auto / cold
+```
+
+| Mode | When fast params are sent | Use it for |
+|------|---------------------------|------------|
+| `normal` (default, `""`) | Never | Cheapest; standard latency |
+| `fast` | Every request | Long interactive sessions where you always want speed |
+| `auto` | Requests in the first `fast_auto_seconds` of **every** turn | Snappy first reply; long tool loops fall back to standard pricing |
+| `cold` | Same window, but only on the **first turn** of a session (no prior history) | Fast onboarding reply, standard pricing afterwards |
+
+`/fast normal|fast|auto|cold` switches the mode for the session; add `--global` to persist to `config.yaml`. `/fast` alone shows the current mode.
+
+**Cost note:** both providers bill fast requests at a multiplier on standard rates (Anthropic: $10 / $50 per MTok in/out on Opus 4.8 and Opus 5), stacking with prompt-cache pricing. `auto`/`cold` bound that premium to the window only. Fast params are only sent to the first-party endpoint that supports them (`api.openai.com` / Codex subscription, `api.anthropic.com`, `api.x.ai`); OpenRouter, Nous Portal, Copilot, Azure, Bedrock, and custom `base_url` routes never receive them in any mode. Only the per-request parameter changes between requests — the system prompt, tools, and messages stay byte-identical, so the prompt cache survives the window boundary.
+
 ## Tool-Use Enforcement
 
 Some models occasionally describe intended actions as text instead of making tool calls ("I would run the tests..." instead of actually calling the terminal). Tool-use enforcement injects system prompt guidance that steers the model back to actually calling tools.