diff --git a/agent/agent_runtime_helpers.py b/agent/agent_runtime_helpers.py
index 1cde73419a44..28f0192d8161 100644
--- a/agent/agent_runtime_helpers.py
+++ b/agent/agent_runtime_helpers.py
@@ -1305,6 +1305,13 @@ def restore_primary_runtime(agent) -> bool:
                         primary_provider or "?",
                     )
 
+        # ── Restore reasoning_config if it was saved ──
+        # switch_model saves reasoning_config in _primary_runtime. If the
+        # snapshot predates that (older sessions), keep the current value.
+        saved_reasoning = rt.get("reasoning_config")
+        if saved_reasoning is not None:
+            agent.reasoning_config = dict(saved_reasoning)
+
         # ── Reset fallback chain for the new turn ──
         agent._fallback_activated = False
         agent._fallback_index = 0
@@ -2065,6 +2072,45 @@ def switch_model(agent, new_model, new_provider, api_key='', base_url='', api_mo
             api_mode=agent.api_mode,
         )
 
+    # ── Re-resolve reasoning_config from per-model override ──
+    # The new model may have a different reasoning_effort override. Re-read
+    # config so the override takes effect immediately on /model switch.
+    # Try both agent.model (normalized, e.g. "claude-opus-4-5") AND the raw
+    # config default (user's original spelling, e.g. "claude-opus-4.5") so
+    # override keys match regardless of how downstream consumers normalized
+    # the input. See plan FINDING #7 + session follow-up.
+    try:
+        from hermes_constants import (
+            parse_reasoning_effort,
+            resolve_per_model_reasoning_effort,
+        )
+        from hermes_cli.config import load_config as _sm_load_config
+
+        _reasoning_cfg = _sm_load_config() or {}
+        _sm_overrides = (_reasoning_cfg.get("agent") or {}).get("reasoning_overrides", {}) or {}
+        # Try the normalized agent.model first, then the raw config default
+        _sm_raw_model_default = str((_reasoning_cfg.get("model") or {}).get("default", "") or "").strip()
+        _sm_per_model = None
+        for _candidate in (agent.model, _sm_raw_model_default):
+            if _candidate:
+                _sm_per_model = resolve_per_model_reasoning_effort(_candidate, _sm_overrides)
+                if _sm_per_model is not None:
+                    break
+        if _sm_per_model is not None:
+            agent.reasoning_config = _sm_per_model
+            logger.info(
+                "switch_model: reasoning_config resolved to per-model override for %s: %s",
+                agent.model, _sm_per_model,
+            )
+        else:
+            # Raw value — a YAML boolean False means thinking disabled,
+            # see parse_reasoning_effort. Do NOT str()/strip() coerce.
+            _sm_global = (_reasoning_cfg.get("agent") or {}).get("reasoning_effort", "")
+            agent.reasoning_config = parse_reasoning_effort(_sm_global)
+            logger.info("switch_model: reasoning_config resolved to global effort: %s", _sm_global or "(none)")
+    except Exception as _reasoning_err:
+        logger.debug("switch_model: could not re-resolve reasoning_config: %s", _reasoning_err)
+
     # ── Invalidate cached system prompt so it rebuilds next turn ──
     agent._cached_system_prompt = None
 
@@ -2087,6 +2133,7 @@ def switch_model(agent, new_model, new_provider, api_key='', base_url='', api_mo
         "client_kwargs": dict(agent._client_kwargs),
         "use_prompt_caching": agent._use_prompt_caching,
         "use_native_cache_layout": agent._use_native_cache_layout,
+        "reasoning_config": dict(agent.reasoning_config) if getattr(agent, "reasoning_config", None) else None,
         "compressor_model": getattr(_cc, "model", agent.model) if _cc else agent.model,
         "compressor_base_url": getattr(_cc, "base_url", agent.base_url) if _cc else agent.base_url,
         "compressor_api_key": getattr(_cc, "api_key", "") if _cc else "",
diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index b93dcf661717..57cc5e76cdb8 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -1635,6 +1635,45 @@ def try_activate_fallback(agent, reason: "FailoverReason | None" = None) -> bool
                 api_mode=agent.api_mode,
             )
 
+        # Re-resolve reasoning_config for the new fallback model (Closes #21256).
+        # Per-model override (if any) takes precedence, else global reasoning_effort.
+        # Wrapped in try/except because config load failure must not kill the swap.
+        try:
+            from hermes_cli.config import load_config
+            from hermes_constants import parse_reasoning_effort, resolve_per_model_reasoning_effort
+
+            _fb_cfg = load_config() or {}
+            _fb_agent_cfg = _fb_cfg.get("agent", {}) or {}
+            _fb_overrides = _fb_agent_cfg.get("reasoning_overrides", {}) or {}
+            _fb_per_model = resolve_per_model_reasoning_effort(agent.model, _fb_overrides)
+            if _fb_per_model is not None:
+                agent.reasoning_config = _fb_per_model
+                logger.info(
+                    "Fallback %s: reasoning_config resolved to per-model override: %s",
+                    agent.model, _fb_per_model,
+                )
+            else:
+                # Raw value — a YAML boolean False means thinking disabled,
+                # see parse_reasoning_effort. Do NOT coerce with ``or ""``.
+                _fb_global_effort = _fb_agent_cfg.get("reasoning_effort", "")
+                agent.reasoning_config = parse_reasoning_effort(_fb_global_effort)
+                if agent.reasoning_config:
+                    logger.info(
+                        "Fallback %s: reasoning_config resolved to global effort: %s",
+                        agent.model, _fb_global_effort,
+                    )
+                else:
+                    logger.info(
+                        "Fallback %s: reasoning_config resolved to None (disabled or default)",
+                        agent.model,
+                    )
+        except Exception as _reasoning_err:
+            logger.debug(
+                "Failed to resolve reasoning_config for fallback %s; keeping current: %s",
+                agent.model, _reasoning_err,
+            )
+            # Keep whatever reasoning_config was active — don't break the fallback swap.
+
         # Keep the prompt's self-identity in sync with the model actually
         # answering, so "what model are you?" doesn't report the primary.
         rewrite_prompt_model_identity(agent, fb_model, fb_provider)
diff --git a/cli-config.yaml.example b/cli-config.yaml.example
index 1858f451c9a4..2583bfb54f0b 100644
--- a/cli-config.yaml.example
+++ b/cli-config.yaml.example
@@ -742,6 +742,19 @@ agent:
   # Options: "xhigh" (max), "high", "medium", "low", "minimal", "none" (disable)
   reasoning_effort: "medium"
   
+  # Per-model reasoning effort overrides (optional dict)
+  # Key: any sensible model spelling works (exact, dots↔dashes interchangeable,
+  #      provider prefix optional). First match wins.
+  # Value: reasoning effort level (same options as reasoning_effort)
+  # Override the global reasoning_effort for that specific model.
+  # NOTE: no `hermes config set` support for this key -- edit YAML directly.
+  # reasoning_overrides:
+  #   "openrouter/anthropic/claude-opus-4.5": "xhigh"
+  #   "openai/gpt-5": "low"
+  #   "claude-opus-4.6": "high"           # bare model name also works
+  #   "deepseek/deepseek-v4-pro": "xhigh" # dots and dashes are interchangeable
+  reasoning_overrides: {}
+  
   # Predefined personalities (use with /personality command)
   personalities:
     helpful: "You are a helpful, friendly AI assistant."
diff --git a/cli.py b/cli.py
index 17d2bdd0e4e3..c836834a2169 100644
--- a/cli.py
+++ b/cli.py
@@ -3917,8 +3917,18 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin):
         )
         
         # Reasoning config (OpenRouter reasoning effort level)
-        self.reasoning_config = _parse_reasoning_config(
-            CLI_CONFIG["agent"].get("reasoning_effort", "")
+        # Per-model override takes precedence over global effort (Closes #21256).
+        _reasoning_overrides = CLI_CONFIG["agent"].get("reasoning_overrides", {}) or {}
+        from hermes_constants import resolve_per_model_reasoning_effort
+        _per_model_reasoning = resolve_per_model_reasoning_effort(
+            self.model, _reasoning_overrides
+        )
+        self.reasoning_config = (
+            _per_model_reasoning
+            if _per_model_reasoning is not None
+            else _parse_reasoning_config(
+                CLI_CONFIG["agent"].get("reasoning_effort", "")
+            )
         )
         self.service_tier = _parse_service_tier_config(
             CLI_CONFIG["agent"].get("service_tier", "")
diff --git a/cron/scheduler.py b/cron/scheduler.py
index a50704ea10be..5e80fc2d7aec 100644
--- a/cron/scheduler.py
+++ b/cron/scheduler.py
@@ -2988,12 +2988,25 @@ def run_job(
         except Exception:
             pass
 
-        # Reasoning config from config.yaml (raw value — a YAML boolean False
-        # means thinking disabled, see parse_reasoning_effort)
-        from hermes_constants import parse_reasoning_effort
-        reasoning_config = parse_reasoning_effort(
-            _cfg.get("agent", {}).get("reasoning_effort", "")
+        # Reasoning config from config.yaml (per-model override > global)
+        from hermes_constants import (
+            parse_reasoning_effort,
+            resolve_per_model_reasoning_effort,
         )
+        _cron_model_cfg = _cfg.get("model", {}) if isinstance(_cfg.get("model", {}), dict) else {}
+        _cron_model = str(
+            _cron_model_cfg.get("default", "") or _cron_model_cfg.get("model", "") or ""
+        ).strip()
+        _cron_overrides = (_cfg.get("agent", {}) or {}).get("reasoning_overrides", {}) or {}
+        _cron_per_model = resolve_per_model_reasoning_effort(_cron_model, _cron_overrides)
+        if _cron_per_model is not None:
+            reasoning_config = _cron_per_model
+        else:
+            # Raw value — a YAML boolean False means thinking disabled,
+            # see parse_reasoning_effort. Do NOT str()/strip() coerce.
+            reasoning_config = parse_reasoning_effort(
+                _cfg.get("agent", {}).get("reasoning_effort", "")
+            )
 
         # Prefill messages from env or config.yaml. The top-level
         # prefill_messages_file key is canonical; agent.prefill_messages_file is
diff --git a/docs/PER_MODEL_REASONING.md b/docs/PER_MODEL_REASONING.md
new file mode 100644
index 000000000000..14a89466d6ee
--- /dev/null
+++ b/docs/PER_MODEL_REASONING.md
@@ -0,0 +1,101 @@
+# Hermes Agent Configuration Guide
+
+## Per-Model Reasoning Effort Overrides
+
+You can configure different reasoning effort levels for different models. This allows you to set `high` effort for complex reasoning models like `claude-opus-4.5` while keeping `medium` for faster models like `gemini-flash`.
+
+### Configuration
+
+Edit your `config.yaml` (typically at `~/.hermes/config.yaml`):
+
+```yaml
+agent:
+  reasoning_overrides:
+    claude-opus-4.5: high
+    gemini-flash: medium
+    gpt-4.5: high
+```
+
+### Key Matching
+
+The model name matching is **spelling-tolerant**. All of these variations will match:
+- `claude-opus-4.5`, `claude-opus-4-5`, `claude-opus.4.5`
+- `anthropic/claude-opus-4.5`, `openrouter/anthropic/claude-opus-4.5`
+- With or without provider prefixes
+
+Exact matches take precedence over variants.
+
+### Resolution Order
+
+When determining reasoning effort for a model, Hermes checks in this order:
+
+1. **Session override**: `/reasoning high` (current session only)
+2. **Per-model override**: `agent.reasoning_overrides.<model>` from config.yaml
+3. **Global default**: `agent.reasoning_effort` from config.yaml
+
+### How It Works
+
+The override applies automatically in these scenarios:
+
+- **CLI startup**: Uses the override for the configured default model
+- **Gateway messaging**: Each gateway session uses the override for its model
+- **Desktop/TUI**: Uses the override for the configured model
+- **Model switching**: When you switch models, the reasoning effort updates to the new model's override
+- **Fallback activation**: When the primary model fails and Hermes falls back to a secondary model, it uses that fallback model's override
+- **Reasoning recovery**: When the primary model recovers after a fallback, the original model's override is restored
+
+### Examples
+
+#### Example 1: High effort for Opus, medium for others
+```yaml
+agent:
+  reasoning_overrides:
+    claude-opus-4.5: high
+```
+
+#### Example 2: Different efforts per model
+```yaml
+agent:
+  reasoning_overrides:
+    claude-opus-4.5: high
+    gemini-2.0-flash: low
+    gpt-4.5: high
+    o3-mini: medium
+```
+
+#### Example 3: With provider prefixes
+```yaml
+agent:
+  reasoning_overrides:
+    anthropic/claude-opus-4.5: high
+    google/gemini-2.0-flash: low
+```
+
+All of these are equivalent — the provider prefix is optional.
+
+### Disabling Reasoning for Specific Models
+
+Set the override to `none` to disable reasoning for a specific model:
+
+```yaml
+agent:
+  reasoning_overrides:
+    gemini-flash: none
+```
+
+### Troubleshooting
+
+**Override not taking effect?**
+- Check the exact model name in your config with `/model`
+- Verify the override is under `agent.reasoning_overrides` (not `agent.reasoning_effort`)
+- Restart the gateway or CLI session after editing config.yaml
+- Check logs for parsing errors
+
+**Override applies but reasoning doesn't work?**
+- Not all models support reasoning (e.g., `gemini-flash` has limited support)
+- Check the model's documentation for reasoning capability
+- Use a model that explicitly supports extended thinking
+
+**Session override not respecting per-model override?**
+- Session overrides take precedence (by design)
+- Clear the session override with `/reasoning default` to return to the per-model override
diff --git a/gateway/run.py b/gateway/run.py
index 8d63da9c952a..7ede7d4130df 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -4852,17 +4852,33 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
 
     @staticmethod
     def _load_reasoning_config() -> dict | None:
-        """Load reasoning effort from config.yaml.
+        """Load reasoning effort from config.yaml, respecting per-model overrides.
 
         Reads agent.reasoning_effort from config.yaml. Valid: "none",
         "minimal", "low", "medium", "high", "xhigh", "max", "ultra". Returns None to use
         default (medium).
+
+        Per-model overrides (agent.reasoning_overrides) take precedence
+        over the global value when the current model matches a key
+        (spelling-tolerant). Closes #21256.
         """
-        from hermes_constants import parse_reasoning_effort
+        from hermes_constants import parse_reasoning_effort, resolve_per_model_reasoning_effort
         cfg = _load_gateway_runtime_config()
-        # Keep the raw value — coercing with ``or ""`` turns a YAML boolean
-        # False (``reasoning_effort: false``/``off``/``no``) into "", silently
-        # re-enabling thinking for users who explicitly disabled it.
+        # Per-model override first
+        model_cfg = cfg.get("model") or {}
+        model = str(
+            (model_cfg.get("default", "") if isinstance(model_cfg, dict) else "")
+            or (model_cfg.get("model", "") if isinstance(model_cfg, dict) else "")
+            or ""
+        ).strip()
+        overrides = (cfg.get("agent") or {}).get("reasoning_overrides", {}) or {}
+        per_model = resolve_per_model_reasoning_effort(model, overrides)
+        if per_model is not None:
+            return per_model
+        # Global fallback — keep the raw value; coercing with ``or ""`` turns
+        # a YAML boolean False (``reasoning_effort: false``/``off``/``no``)
+        # into "", silently re-enabling thinking for users who explicitly
+        # disabled it.
         effort = cfg_get(cfg, "agent", "reasoning_effort", default="")
         result = parse_reasoning_effort(effort)
         if effort and str(effort).strip() and result is None:
diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index 0754933d6082..737833fae208 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -1158,8 +1158,15 @@ DEFAULT_CONFIG = {
         # only controls how inbound user images are presented.
         "image_input_mode": "auto",
         "disabled_toolsets": [],
+
+        # Per-model reasoning effort overrides (spelling-tolerant).
+        # Dict mapping model names (any reasonable spelling) to effort levels.
+        # Takes precedence over agent.reasoning_effort when the current model
+        # matches a key in this dict.
+        # Edit directly in config.yaml (no CLI support due to dots in keys).
+        "reasoning_overrides": {},
     },
-    
+
     "terminal": {
         "backend": "local",
         "modal_mode": "auto",
diff --git a/hermes_constants.py b/hermes_constants.py
index 26842530c22d..5d64a619ecaa 100644
--- a/hermes_constants.py
+++ b/hermes_constants.py
@@ -823,6 +823,131 @@ def parse_reasoning_effort(effort) -> dict | None:
     return None
 
 
+def _canonical_model_variants(model: str) -> list[str]:
+    """Generate bounded spelling variants for tolerant override matching.
+
+    Model names mix two types of separators:
+    - **Word separators**: dashes between words (``claude-opus``)
+    - **Version separators**: dots or dashes between version digits (``4.5``, ``4-5``)
+
+    The tricky case is that ``.`` appears in BOTH roles (word sep in some
+    spellings, version sep in others), so a blanket ``.replace('.', '-')``
+    is lossy — it collapses version dots into dashes and no later step
+    recovers the canonical form (``claude-opus-4.5``).
+
+    Strategy: generate a small set of base forms, then apply version-dot
+    recovery to EACH of them. This ensures symmetry:
+    ``claude-opus-4.5``, ``claude-opus-4-5``, and ``claude-opus.4.5`` all
+    produce the same variant set.
+
+    Steps:
+    1. Exact input
+    2. Dots/dashes cross-substitution on the entire string
+    3. Version-dot recovery applied to ALL derivatives
+    4. Strip provider/aggregator prefix → bare model variants
+    5. Apply version-dot recovery to bare derivatives
+    6. Prepend known provider/aggregator prefixes
+
+    Duplicates removed in insertion order (exact always wins).
+    """
+    import re
+
+    # Version-dot regexes — digit-separator-digit interconversion
+    _dash_to_dot = lambda s: re.sub(r'(\d)-(\d)', r'\1.\2', s)
+    _dot_to_dash = lambda s: re.sub(r'(\d)\.(\d)', r'\1-\2', s)
+
+    seen = set()
+    variants = []
+
+    def _add(v):
+        if v and v not in seen:
+            seen.add(v)
+            variants.append(v)
+
+    def _add_with_derivatives(s):
+        """Add s plus its dots↔dashes and version-dot derivatives."""
+        _add(s)
+        all_dashed = s.replace('.', '-')
+        _add(all_dashed)
+        all_dotted = s.replace('-', '.')
+        _add(all_dotted)
+        # Version-dot recovery on each base form
+        _add(_dash_to_dot(s))
+        _add(_dot_to_dash(s))
+        _add(_dash_to_dot(all_dashed))
+        _add(_dot_to_dash(all_dotted))
+
+    # 1-3. Base variants for the full string
+    _add_with_derivatives(model)
+
+    # Split by / to handle provider prefix
+    parts = model.split('/')
+
+    # 4. Bare model variants (strip provider/aggregator prefix)
+    if len(parts) >= 2:
+        bare = parts[-1]
+        _add_with_derivatives(bare)
+
+    # Strip aggregator only (3+ parts)
+    # e.g. "openrouter/anthropic/claude-opus-4.5" → "anthropic/claude-opus-4.5"
+    if len(parts) >= 3:
+        _add_with_derivatives('/'.join(parts[1:]))
+
+    # 5. Prepend known provider prefixes to bare variants
+    known_providers = (
+        'anthropic', 'openai', 'google', 'openrouter', 'groq', 'mistral',
+        'xai', 'cohere', 'perplexity', 'together', 'fireworks', 'deepseek',
+    )
+    bare_variants = [v for v in variants if '/' not in v]
+    for v in bare_variants:
+        for provider in known_providers:
+            _add(f"{provider}/{v}")
+
+    # Prepend aggregator to single-slash variants
+    single_slash_variants = [v for v in variants if v.count('/') == 1]
+    known_aggregators = ('openrouter', 'opencode', 'fireworks', 'groq', 'together')
+    for v in single_slash_variants:
+        for agg in known_aggregators:
+            _add(f"{agg}/{v}")
+
+    return variants
+
+
+def resolve_per_model_reasoning_effort(model: str, overrides: dict | None) -> dict | None:
+    """Lookup a per-model reasoning_effort override with spelling-tolerance.
+
+    Args:
+        model: The model string (any spelling — exact, normalized, bare,
+               with provider prefix, etc.)
+        overrides: The dict of per-model overrides from
+                   agent.reasoning_overrides in config.yaml. Keys can be
+                   any sensible spelling of the model name.
+
+    Returns:
+        The parsed reasoning_config dict if a match is found,
+        None otherwise (caller should fall back to global reasoning_effort).
+
+    Resolution order:
+    1. Exact match
+    2. Dots ↔ dashes variants
+    3. Strip provider prefix (bare model name only)
+    4. Strip aggregator prefix (middle segment only)
+    5. Prepend known aggregator prefixes to bare/single-slash variants
+
+    First non-None parse_reasoning_effort result wins.
+    """
+    if not overrides or not isinstance(overrides, dict) or not model:
+        return None
+
+    for variant in _canonical_model_variants(model):
+        if variant in overrides:
+            result = parse_reasoning_effort(overrides[variant])
+            if result is not None:
+                return result
+
+    return None
+
+
 def is_termux() -> bool:
     """Return True when running inside a Termux (Android) environment.
 
diff --git a/tests/cron/test_reasoning_config_per_model.py b/tests/cron/test_reasoning_config_per_model.py
new file mode 100644
index 000000000000..bdd09ade118b
--- /dev/null
+++ b/tests/cron/test_reasoning_config_per_model.py
@@ -0,0 +1,106 @@
+"""Tests for per-model reasoning_effort override in cron scheduler."""
+
+import pytest
+
+
+class TestCronPerModelReasoningConfig:
+    """Test cron scheduler respects per-model reasoning overrides.
+
+    Rather than spinning up a full CronScheduler (heavy), we verify the
+    resolution logic by testing the helper directly against a config dict
+    shaped the same way the scheduler reads it.
+    """
+
+    def test_per_model_override_resolves_for_cron_model(self):
+        """The spelling-tolerant helper resolves the cron config's model."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+
+        # Simulate cron scheduler config shape
+        _cfg = {
+            "model": {"default": "anthropic/claude-opus-4.5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+        _model_cfg = _cfg.get("model", {})
+        _model = str(_model_cfg.get("default", "") or "").strip()
+        _overrides = (_cfg.get("agent", {}) or {}).get("reasoning_overrides", {}) or {}
+
+        result = resolve_per_model_reasoning_effort(_model, _overrides)
+        assert result is not None
+        assert result["effort"] == "xhigh"
+
+    def test_cron_falls_back_to_global_when_no_override(self):
+        """When no per-model override matches, global effort is used."""
+        from hermes_constants import parse_reasoning_effort, resolve_per_model_reasoning_effort
+
+        _cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": "low",
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+        _model = _cfg["model"]["default"]
+        _overrides = _cfg["agent"]["reasoning_overrides"]
+
+        per_model = resolve_per_model_reasoning_effort(_model, _overrides)
+        assert per_model is None  # no match
+
+        # Scheduler falls back to global
+        effort = _cfg["agent"]["reasoning_effort"]
+        result = parse_reasoning_effort(effort)
+        assert result is not None
+        assert result["effort"] == "low"
+
+    def test_cron_handles_missing_model_key(self):
+        """Works when config has no model.default."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+
+        _cfg = {
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {"claude-opus-4.5": "high"},
+            },
+        }
+        _model_cfg = _cfg.get("model", {}) if isinstance(_cfg.get("model", {}), dict) else {}
+        _model = str(_model_cfg.get("default", "") or _model_cfg.get("model", "") or "").strip()
+        _overrides = (_cfg.get("agent", {}) or {}).get("reasoning_overrides", {}) or {}
+
+        # Empty model → resolve returns None → scheduler uses global
+        result = resolve_per_model_reasoning_effort(_model, _overrides)
+        assert result is None
+
+    def test_global_fallback_with_yaml_false(self):
+        """YAML boolean False must reach parse_reasoning_effort uncoerced.
+
+        Regression: str(... or "").strip() turned False into "", silently
+        re-enabling thinking. The raw value must pass through so
+        parse_reasoning_effort(False) returns {'enabled': False}.
+        """
+        from hermes_constants import parse_reasoning_effort, resolve_per_model_reasoning_effort
+
+        _cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": False,  # YAML boolean, not string
+                "reasoning_overrides": {"claude-opus-4.5": "xhigh"},
+            },
+        }
+        _model = _cfg["model"]["default"]
+        _overrides = _cfg["agent"]["reasoning_overrides"]
+
+        per_model = resolve_per_model_reasoning_effort(_model, _overrides)
+        assert per_model is None  # no match
+
+        # Scheduler global fallback — raw value, no coercion
+        result = parse_reasoning_effort(
+            _cfg.get("agent", {}).get("reasoning_effort", "")
+        )
+        assert result is not None
+        assert result.get("enabled") is False
diff --git a/tests/gateway/test_reasoning_config_per_model.py b/tests/gateway/test_reasoning_config_per_model.py
new file mode 100644
index 000000000000..f9799de33198
--- /dev/null
+++ b/tests/gateway/test_reasoning_config_per_model.py
@@ -0,0 +1,111 @@
+"""Tests for per-model reasoning_effort override in gateway _load_reasoning_config."""
+
+import pytest
+
+import gateway.run as gateway_run
+
+
+class TestGatewayPerModelReasoningConfig:
+    """Test GatewayRunner._load_reasoning_config respects per-model overrides."""
+
+    def test_per_model_override_takes_precedence(self, monkeypatch):
+        """Per-model override wins over global reasoning_effort."""
+        from hermes_cli.config import DEFAULT_CONFIG
+
+        fake_cfg = {
+            "model": {"default": "anthropic/claude-opus-4.5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+        monkeypatch.setattr(gateway_run, "_load_gateway_runtime_config", lambda: fake_cfg)
+
+        result = gateway_run.GatewayRunner._load_reasoning_config()
+        assert result is not None
+        assert result["enabled"] is True
+        assert result["effort"] == "xhigh"
+
+    def test_global_fallback_when_no_override(self, monkeypatch):
+        """Global reasoning_effort applies when no per-model override matches."""
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": "high",
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+        monkeypatch.setattr(gateway_run, "_load_gateway_runtime_config", lambda: fake_cfg)
+
+        result = gateway_run.GatewayRunner._load_reasoning_config()
+        assert result is not None
+        assert result["effort"] == "high"
+
+    def test_spelling_tolerant_match_in_gateway(self, monkeypatch):
+        """Override matches even with different spelling (dots vs dashes)."""
+        fake_cfg = {
+            "model": {"default": "claude-opus-4-5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {
+                    "claude-opus-4.5": "xhigh",  # key has dots, model has dashes
+                },
+            },
+        }
+        monkeypatch.setattr(gateway_run, "_load_gateway_runtime_config", lambda: fake_cfg)
+
+        result = gateway_run.GatewayRunner._load_reasoning_config()
+        assert result is not None
+        assert result["effort"] == "xhigh"
+
+    def test_no_overrides_dict(self, monkeypatch):
+        """Works fine when reasoning_overrides key is absent."""
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": "low",
+            },
+        }
+        monkeypatch.setattr(gateway_run, "_load_gateway_runtime_config", lambda: fake_cfg)
+
+        result = gateway_run.GatewayRunner._load_reasoning_config()
+        assert result is not None
+        assert result["effort"] == "low"
+
+    def test_empty_overrides(self, monkeypatch):
+        """Empty overrides dict falls back to global."""
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {},
+            },
+        }
+        monkeypatch.setattr(gateway_run, "_load_gateway_runtime_config", lambda: fake_cfg)
+
+        result = gateway_run.GatewayRunner._load_reasoning_config()
+        assert result is not None
+        assert result["effort"] == "medium"
+
+    def test_global_fallback_with_yaml_false(self, monkeypatch):
+        """YAML boolean False must reach parse_reasoning_effort uncoerced.
+
+        Regression: str(... or "").strip() turned False into "", silently
+        re-enabling thinking. The raw value must pass through so
+        parse_reasoning_effort(False) returns {'enabled': False}.
+        """
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": False,  # YAML boolean, not string
+            },
+        }
+        monkeypatch.setattr(gateway_run, "_load_gateway_runtime_config", lambda: fake_cfg)
+
+        result = gateway_run.GatewayRunner._load_reasoning_config()
+        assert result is not None
+        assert result.get("enabled") is False
diff --git a/tests/run_agent/test_fallback_reasoning_override.py b/tests/run_agent/test_fallback_reasoning_override.py
new file mode 100644
index 000000000000..1c2c3e6228a7
--- /dev/null
+++ b/tests/run_agent/test_fallback_reasoning_override.py
@@ -0,0 +1,144 @@
+"""Tests for per-model reasoning_effort override during fallback activation.
+
+Tests that try_activate_fallback re-resolves reasoning_config when
+swapping to a fallback model, so per-model overrides are honored even
+during error recovery.
+"""
+
+import pytest
+from unittest.mock import MagicMock, patch
+
+
+class TestFallbackReasoningOverride:
+    """Test try_activate_fallback re-resolves reasoning_config."""
+
+    def test_fallback_re_resolves_reasoning_config(self):
+        """When fallback activates, reasoning_config should be re-resolved.
+
+        We test the resolution logic directly rather than spinning up a
+        full try_activate_fallback (which requires extensive agent setup).
+        The production code calls resolve_per_model_reasoning_effort with
+        the fallback model string — we verify that works correctly.
+        """
+        from hermes_constants import resolve_per_model_reasoning_effort
+
+        # Simulate: primary was gemini-flash (medium), fallback to claude-opus-4.5 (xhigh)
+        overrides = {
+            "claude-opus-4.5": "xhigh",
+            "gemini-flash": "medium",
+        }
+
+        # Fallback model lookup
+        fb_result = resolve_per_model_reasoning_effort("claude-opus-4.5", overrides)
+        assert fb_result is not None
+        assert fb_result["effort"] == "xhigh"
+
+        # Primary model lookup (for comparison)
+        primary_result = resolve_per_model_reasoning_effort("gemini-flash", overrides)
+        assert primary_result is not None
+        assert primary_result["effort"] == "medium"
+
+        # The key point: fallback result differs from primary
+        assert fb_result["effort"] != primary_result["effort"]
+
+    def test_fallback_to_model_without_override_uses_global(self):
+        """Fallback to a model with no override should resolve to None (→ global)."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+
+        overrides = {"claude-opus-4.5": "xhigh"}
+
+        # Fallback to gpt-5 which has no override
+        result = resolve_per_model_reasoning_effort("gpt-5", overrides)
+        assert result is None  # caller falls back to global
+
+    def test_fallback_with_normalized_model_name(self):
+        """Fallback model name may be normalized (dots→dashes); override should still match."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+
+        # User wrote key with dots, but normalize_model_for_provider converts to dashes
+        overrides = {"claude-sonnet-4.6": "high"}
+
+        result = resolve_per_model_reasoning_effort("claude-sonnet-4-6", overrides)
+        assert result is not None
+        assert result["effort"] == "high"
+
+    def test_fallback_recovery_restores_primary_reasoning(self):
+        """After fallback + restore_primary_runtime, reasoning_config returns to primary's value.
+
+        This tests the integration of Task 6 (_primary_runtime snapshot) with
+        Task 6b (fallback re-resolution). The full cycle:
+        1. Primary model = gemini-flash, reasoning = medium
+        2. /model switch → _primary_runtime captures reasoning_config
+        3. Fallback activates → reasoning re-resolved for fallback model
+        4. restore_primary_runtime → reasoning_config restored from snapshot
+        """
+        from agent.agent_runtime_helpers import restore_primary_runtime
+
+        agent = MagicMock()
+        # Simulate: _primary_runtime was captured during /model switch
+        agent._primary_runtime = {
+            "model": "gemini-flash",
+            "provider": "google",
+            "base_url": "",
+            "api_mode": "openai",
+            "api_key": "key",
+            "client_kwargs": {},
+            "use_prompt_caching": False,
+            "use_native_cache_layout": False,
+            "reasoning_config": {"enabled": True, "effort": "medium"},
+            "compressor_model": "gemini-flash",
+            "compressor_base_url": "",
+            "compressor_api_key": "",
+            "compressor_provider": "",
+            "compressor_context_length": 0,
+            "compressor_api_mode": "",
+            "compressor_threshold_tokens": 0,
+        }
+        agent._fallback_activated = True
+        agent._fallback_index = 0
+        agent._fallback_chain = []
+        agent._fallback_model = None
+        agent._transport_cache = {}
+        agent._config_context_length = None
+        agent._rate_limited_until = 0
+        # During fallback, reasoning was changed to xhigh (fallback model's override)
+        agent.model = "claude-opus-4.5"
+        agent.provider = "anthropic"
+        agent.reasoning_config = {"enabled": True, "effort": "xhigh"}
+        agent.context_compressor = MagicMock()
+        agent.base_url = ""
+        agent._anthropic_prompt_cache_policy = MagicMock(return_value=(False, False))
+        agent._create_openai_client = MagicMock(return_value=MagicMock())
+        agent._ensure_lmstudio_runtime_loaded = MagicMock()
+
+        result = restore_primary_runtime(agent)
+        assert result is True
+        # reasoning_config should be restored to primary's value (medium)
+        assert agent.reasoning_config == {"enabled": True, "effort": "medium"}
+
+    def test_fallback_global_fallback_with_yaml_false(self):
+        """Fallback global fallback must not coerce YAML boolean False.
+
+        Regression: ``or ""`` turned False into "", silently re-enabling
+        thinking. The raw value must pass through so
+        parse_reasoning_effort(False) returns {'enabled': False}.
+
+        The production code in try_activate_fallback does:
+            _fb_global_effort = _fb_agent_cfg.get("reasoning_effort", "")
+            agent.reasoning_config = parse_reasoning_effort(_fb_global_effort)
+        We verify that passing the raw False (not coerced "") produces
+        the disabled config.
+        """
+        from hermes_constants import parse_reasoning_effort
+
+        # Simulate: no per-model override matches, global is YAML False
+        _fb_agent_cfg = {"reasoning_effort": False}
+
+        # This is the exact line from try_activate_fallback's else branch.
+        # The bug was: _fb_global_effort = _fb_agent_cfg.get(...) or ""
+        # which turned False into "". The fix passes the raw value.
+        _fb_global_effort = _fb_agent_cfg.get("reasoning_effort", "")
+        result = parse_reasoning_effort(_fb_global_effort)
+
+        assert result is not None
+        assert result.get("enabled") is False
diff --git a/tests/run_agent/test_switch_model_reasoning_override.py b/tests/run_agent/test_switch_model_reasoning_override.py
new file mode 100644
index 000000000000..ae304e118df3
--- /dev/null
+++ b/tests/run_agent/test_switch_model_reasoning_override.py
@@ -0,0 +1,220 @@
+"""Tests for per-model reasoning_effort override during /model switch.
+
+Tests that switch_model:
+1. Re-resolves reasoning_config when switching to a model with an override
+2. Falls back to global when switching to a model without an override
+3. Saves reasoning_config into _primary_runtime for fallback recovery
+"""
+
+import pytest
+from unittest.mock import MagicMock, patch
+
+
+class TestSwitchModelReasoningOverride:
+    """Test switch_model re-resolves reasoning_config on model switch."""
+
+    def _make_fake_agent(self, model="gpt-5", provider="openai"):
+        """Create a minimal fake agent for switch_model testing."""
+        agent = MagicMock()
+        agent.model = model
+        agent.provider = provider
+        agent.base_url = "https://api.openai.com/v1"
+        agent.api_mode = "openai"
+        agent.api_key = "test-key"
+        agent._client_kwargs = {"api_key": "test-key", "base_url": "https://api.openai.com/v1"}
+        agent._use_prompt_caching = False
+        agent._use_native_cache_layout = False
+        agent.reasoning_config = {"enabled": True, "effort": "medium"}
+        agent._fallback_activated = False
+        agent._fallback_index = 0
+        agent._fallback_chain = []
+        agent._fallback_model = None
+        agent._config_context_length = None
+        agent._transport_cache = {}
+        agent.context_compressor = None
+        agent._cached_system_prompt = None
+        agent._anthropic_api_key = ""
+        agent._anthropic_base_url = None
+        agent._is_anthropic_oauth = False
+        agent._anthropic_prompt_cache_policy = MagicMock(
+            return_value=(False, False)
+        )
+        agent._ensure_lmstudio_runtime_loaded = MagicMock()
+        agent._create_openai_client = MagicMock(return_value=MagicMock())
+        return agent
+
+    def test_primary_runtime_includes_reasoning_config(self):
+        """After switch_model, _primary_runtime should contain reasoning_config key."""
+        from agent.agent_runtime_helpers import switch_model
+
+        agent = self._make_fake_agent()
+
+        fake_cfg = {
+            "model": {"default": "claude-opus-4.5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {
+                    "claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+
+        with patch("hermes_cli.config.load_config", return_value=fake_cfg):
+            try:
+                switch_model(
+                    agent,
+                    new_model="claude-opus-4.5",
+                    new_provider="anthropic",
+                    base_url="https://api.anthropic.com",
+                    api_mode="anthropic_messages",
+                )
+            except Exception:
+                # Client creation may fail in test env; check _primary_runtime was set
+                pass
+
+        assert hasattr(agent, "_primary_runtime")
+        assert "reasoning_config" in agent._primary_runtime
+
+    def test_reasoning_config_resolves_to_override_on_switch(self):
+        """switch_model should resolve reasoning_config to per-model override."""
+        from agent.agent_runtime_helpers import switch_model
+
+        agent = self._make_fake_agent()
+
+        fake_cfg = {
+            "model": {"default": "claude-opus-4.5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {
+                    "claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+
+        with patch("hermes_cli.config.load_config", return_value=fake_cfg):
+            try:
+                switch_model(
+                    agent,
+                    new_model="claude-opus-4.5",
+                    new_provider="anthropic",
+                    base_url="https://api.anthropic.com",
+                    api_mode="anthropic_messages",
+                )
+            except Exception:
+                pass
+
+        # reasoning_config should be updated to xhigh
+        assert agent.reasoning_config is not None
+        assert agent.reasoning_config.get("effort") == "xhigh"
+
+    def test_reasoning_config_falls_back_to_global(self):
+        """switch_model should fall back to global when no override for new model."""
+        from agent.agent_runtime_helpers import switch_model
+
+        agent = self._make_fake_agent()
+
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": "low",
+                "reasoning_overrides": {
+                    "claude-opus-4.5": "xhigh",  # override for different model
+                },
+            },
+        }
+
+        with patch("hermes_cli.config.load_config", return_value=fake_cfg):
+            try:
+                switch_model(
+                    agent,
+                    new_model="gpt-5",
+                    new_provider="openai",
+                    api_mode="openai",
+                )
+            except Exception:
+                pass
+
+        # No override for gpt-5 → should fall back to global "low"
+        assert agent.reasoning_config is not None
+        assert agent.reasoning_config.get("effort") == "low"
+
+    def test_restore_primary_runtime_restores_reasoning(self):
+        """restore_primary_runtime should restore reasoning_config from snapshot."""
+        from agent.agent_runtime_helpers import restore_primary_runtime
+
+        agent = MagicMock()
+        agent._primary_runtime = {
+            "model": "claude-opus-4.5",
+            "provider": "anthropic",
+            "base_url": "https://api.anthropic.com",
+            "api_mode": "anthropic_messages",
+            "api_key": "key",
+            "client_kwargs": {},
+            "use_prompt_caching": True,
+            "use_native_cache_layout": False,
+            "reasoning_config": {"enabled": True, "effort": "xhigh"},
+            "compressor_model": "claude-opus-4.5",
+            "compressor_base_url": "",
+            "compressor_api_key": "",
+            "compressor_provider": "",
+            "compressor_context_length": 0,
+            "compressor_api_mode": "",
+            "compressor_threshold_tokens": 0,
+            "anthropic_api_key": "key",
+            "anthropic_base_url": "https://api.anthropic.com",
+            "is_anthropic_oauth": False,
+        }
+        agent._fallback_activated = True
+        agent._fallback_index = 0
+        agent._fallback_chain = []
+        agent._fallback_model = None
+        agent._transport_cache = {}
+        agent._config_context_length = None
+        agent._rate_limited_until = 0
+        agent.model = "fallback-model"
+        agent.provider = "openai"
+        agent.reasoning_config = {"enabled": True, "effort": "medium"}
+        agent.context_compressor = MagicMock()
+        agent.base_url = ""
+        # Mock the methods restore_primary_runtime calls
+        agent._anthropic_prompt_cache_policy = MagicMock(return_value=(True, False))
+        agent._create_openai_client = MagicMock(return_value=MagicMock())
+        agent._ensure_lmstudio_runtime_loaded = MagicMock()
+
+        result = restore_primary_runtime(agent)
+        assert result is True
+        assert agent.reasoning_config == {"enabled": True, "effort": "xhigh"}
+
+    def test_switch_model_global_fallback_with_yaml_false(self):
+        """switch_model global fallback must not coerce YAML boolean False.
+
+        Regression: str(... or "").strip() turned False into "", silently
+        re-enabling thinking. The raw value must pass through so
+        parse_reasoning_effort(False) returns {'enabled': False}.
+        """
+        from agent.agent_runtime_helpers import switch_model
+
+        agent = self._make_fake_agent()
+
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": False,  # YAML boolean, not string
+                "reasoning_overrides": {},
+            },
+        }
+
+        with patch("hermes_cli.config.load_config", return_value=fake_cfg):
+            try:
+                switch_model(
+                    agent,
+                    new_model="gpt-5",
+                    new_provider="openai",
+                    api_mode="openai",
+                )
+            except Exception:
+                pass
+
+        # No override for gpt-5 → global fallback with raw False
+        assert agent.reasoning_config is not None
+        assert agent.reasoning_config.get("enabled") is False
\ No newline at end of file
diff --git a/tests/test_hermes_constants.py b/tests/test_hermes_constants.py
index 44a449d91d08..5c70ebcb952b 100644
--- a/tests/test_hermes_constants.py
+++ b/tests/test_hermes_constants.py
@@ -490,6 +490,206 @@ class TestParseReasoningEffort:
         assert documented.issubset(set(VALID_REASONING_EFFORTS))
 
 
+class TestResolvePerModelReasoningEffort:
+    """Tests for resolve_per_model_reasoning_effort() — spelling-tolerant
+    per-model override lookup from agent.reasoning_overrides dict.
+
+    Contract: the override key the user writes in config.yaml should match
+    regardless of how downstream consumers normalize the model string.
+    normalize_model_for_provider() converts dots to dashes and
+    adds/strips provider prefixes. Our resolver tolerates these
+    variations so the user's intent ("this model always gets xhigh")
+    is honored no matter which code path feeds the model string.
+    """
+
+    def test_exact_match(self):
+        """Exact model string match returns the parsed override."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "xhigh"}
+        result = resolve_per_model_reasoning_effort("claude-opus-4.5", overrides)
+        assert result == {"enabled": True, "effort": "xhigh"}
+
+    def test_none_when_no_matching_key(self):
+        """Model not in overrides returns None (caller falls back to global)."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "xhigh"}
+        assert resolve_per_model_reasoning_effort("gpt-5", overrides) is None
+
+    def test_none_value_returns_disabled(self):
+        """Override set to 'none' returns {'enabled': False}."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "none"}
+        result = resolve_per_model_reasoning_effort("claude-opus-4.5", overrides)
+        assert result == {"enabled": False}
+
+    def test_invalid_value_returns_none(self):
+        """Override with invalid effort falls back to None (global)."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "banana"}
+        assert resolve_per_model_reasoning_effort("claude-opus-4.5", overrides) is None
+
+    def test_none_or_empty_overrides_returns_none(self):
+        """None or empty overrides dict returns None."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        assert resolve_per_model_reasoning_effort("claude-opus-4.5", None) is None
+        assert resolve_per_model_reasoning_effort("claude-opus-4.5", {}) is None
+
+    def test_empty_model_returns_none(self):
+        """Empty model string returns None."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        assert resolve_per_model_reasoning_effort("", {"gpt-5": "low"}) is None
+
+    # --- Spelling tolerance layer ---
+
+    def test_dots_to_dashes_variant(self):
+        """User wrote key with dots; input comes in normalized with dashes.
+
+        normalize_model_for_provider converts claude-opus-4.5 → claude-opus-4-5
+        for the anthropic provider. The user's override key should still match.
+        """
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "xhigh"}
+        result = resolve_per_model_reasoning_effort("claude-opus-4-5", overrides)
+        assert result == {"enabled": True, "effort": "xhigh"}
+
+    def test_dashes_to_dots_variant(self):
+        """User wrote key with dashes; input comes in with dots."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4-5": "high"}
+        result = resolve_per_model_reasoning_effort("claude-opus.4.5", overrides)
+        assert result == {"enabled": True, "effort": "high"}
+
+    def test_strip_provider_prefix(self):
+        """User wrote key WITH provider prefix; input comes in bare.
+
+        E.g. user config: model.default: claude-opus-4.5 (no prefix),
+        but override key: anthropic/claude-opus-4.5.
+        """
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"anthropic/claude-opus-4.5": "high"}
+        result = resolve_per_model_reasoning_effort("claude-opus-4.5", overrides)
+        assert result == {"enabled": True, "effort": "high"}
+
+    def test_prepend_provider_prefix(self):
+        """User wrote key bare; input comes in WITH provider prefix.
+
+        E.g. user config: model.default: anthropic/claude-opus-4.5,
+        but override key: claude-opus-4.5 (no prefix).
+        """
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "high"}
+        result = resolve_per_model_reasoning_effort("anthropic/claude-opus-4.5", overrides)
+        assert result == {"enabled": True, "effort": "high"}
+
+    def test_aggregator_prefix_stripping(self):
+        """openrouter/anthropic/claude-opus-4.5 should match key anthropic/claude-opus-4.5.
+
+        Aggregator providers (openrouter) prepend their own name,
+        creating a triple-prefix. The resolver strips the aggregator
+        layer to find the user's two-segment key.
+        """
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"anthropic/claude-opus-4.5": "xhigh"}
+        result = resolve_per_model_reasoning_effort("openrouter/anthropic/claude-opus-4.5", overrides)
+        assert result == {"enabled": True, "effort": "xhigh"}
+
+    def test_exact_match_wins_over_variant(self):
+        """Ambiguity resolution: exact match takes priority over a variant.
+
+        If both 'claude-opus-4.5' (exact) and 'claude-opus-4-5' (dashes
+        variant) are keys, the exact input matches the exact key first.
+        """
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "high", "claude-opus-4-5": "xhigh"}
+        result = resolve_per_model_reasoning_effort("claude-opus-4.5", overrides)
+        assert result == {"enabled": True, "effort": "high"}
+
+    def test_none_when_no_variant_matches(self):
+        """All variants exhausted without a match returns None."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"gpt-5": "low"}
+        assert resolve_per_model_reasoning_effort("claude-opus-4.5", overrides) is None
+
+    def test_all_dotted_input_matches_canonical_key(self):
+        """Regression: all-dotted input (claude-opus.4.5) must match
+        canonical key (claude-opus-4.5).
+
+        This was a real bug found by delegate review: the old
+        all_dashed = model.replace('.', '-') collapsed version dots,
+        making the canonical form unreachable from all-dotted input.
+        """
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"claude-opus-4.5": "xhigh"}
+        result = resolve_per_model_reasoning_effort("claude-opus.4.5", overrides)
+        assert result is not None
+        assert result["effort"] == "xhigh"
+
+    def test_different_models_do_not_match(self):
+        """No false positives: gemini-2.0-flash must not match gemini-flash."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        overrides = {"gemini-flash": "low"}
+        assert resolve_per_model_reasoning_effort("gemini-2.0-flash", overrides) is None
+
+
+class TestReasoningOverridesDefaultConfig:
+    """Tests for the agent.reasoning_overrides default config key (Task 2)."""
+
+    def test_default_config_has_reasoning_overrides_key(self):
+        """DEFAULT_CONFIG['agent'] contains 'reasoning_overrides' as an empty dict."""
+        from hermes_cli.config import DEFAULT_CONFIG
+        assert "reasoning_overrides" in DEFAULT_CONFIG["agent"]
+        assert DEFAULT_CONFIG["agent"]["reasoning_overrides"] == {}
+
+    def test_config_version_bumped(self):
+        """Config version was bumped to signal the schema change for reasoning_overrides."""
+        from hermes_cli.config import DEFAULT_CONFIG
+        assert DEFAULT_CONFIG.get("_config_version") >= 31
+
+    def test_load_config_preserves_user_reasoning_overrides(self, tmp_path, monkeypatch):
+        """User-added reasoning_overrides are preserved through load_config()."""
+        import yaml
+        from hermes_cli.config import load_config, get_config_path
+
+        user_config = {
+            "agent": {
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4-5": "high",
+                    "openrouter/anthropic/claude-sonnet-4-6": "low",
+                }
+            }
+        }
+        config_path = tmp_path / "config.yaml"
+        config_path.write_text(yaml.safe_dump(user_config))
+
+        # load_config() reads from get_config_path() — patch its global reference
+        monkeypatch.setitem(
+            load_config.__globals__, "get_config_path", lambda: config_path
+        )
+
+        loaded = load_config()
+        assert loaded["agent"]["reasoning_overrides"] == {
+            "anthropic/claude-opus-4-5": "high",
+            "openrouter/anthropic/claude-sonnet-4-6": "low",
+        }
+
+    def test_spelling_tolerant_lookup_works_with_user_config(self):
+        """resolve_per_model_reasoning_effort works with user-added overrides."""
+        from hermes_constants import resolve_per_model_reasoning_effort
+        # User config with one override, query uses different spelling
+        overrides = {
+            "anthropic/claude-opus-4.5": "xhigh",  # user wrote with dots
+        }
+        # Lookup with different spelling (bare, dashes) — should still match
+        result = resolve_per_model_reasoning_effort("claude-opus-4-5", overrides)
+        assert result == {"enabled": True, "effort": "xhigh"}
+
+        # Another override, bare key
+        overrides2 = {"gpt-5": "low"}
+        # Lookup with provider prefix — should match
+        result2 = resolve_per_model_reasoning_effort("openai/gpt-5", overrides2)
+        assert result2 == {"enabled": True, "effort": "low"}
+
+
 class TestSecureParentDir:
     """Tests for secure_parent_dir() — prevents chmod on / or top-level dirs."""
 
diff --git a/tests/tui_gateway/test_reasoning_config_per_model.py b/tests/tui_gateway/test_reasoning_config_per_model.py
new file mode 100644
index 000000000000..d3468ff530a9
--- /dev/null
+++ b/tests/tui_gateway/test_reasoning_config_per_model.py
@@ -0,0 +1,100 @@
+"""Tests for per-model reasoning_effort override in TUI gateway _load_reasoning_config."""
+
+import pytest
+
+import tui_gateway.server as tui_server
+
+
+class TestTUIPerModelReasoningConfig:
+    """Test tui_gateway _load_reasoning_config respects per-model overrides."""
+
+    def test_per_model_override_takes_precedence(self, monkeypatch):
+        """Per-model override wins over global reasoning_effort."""
+        fake_cfg = {
+            "model": {"default": "anthropic/claude-opus-4.5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+        monkeypatch.setattr(tui_server, "_load_cfg", lambda: fake_cfg)
+
+        result = tui_server._load_reasoning_config()
+        assert result is not None
+        assert result["enabled"] is True
+        assert result["effort"] == "xhigh"
+
+    def test_global_fallback_when_no_override(self, monkeypatch):
+        """Global reasoning_effort applies when no per-model override matches."""
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": "high",
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4.5": "xhigh",
+                },
+            },
+        }
+        monkeypatch.setattr(tui_server, "_load_cfg", lambda: fake_cfg)
+
+        result = tui_server._load_reasoning_config()
+        assert result is not None
+        assert result["effort"] == "high"
+
+    def test_spelling_tolerant_match(self, monkeypatch):
+        """Override matches even with different spelling (provider prefix)."""
+        fake_cfg = {
+            "model": {"default": "claude-opus-4.5"},
+            "agent": {
+                "reasoning_effort": "medium",
+                "reasoning_overrides": {
+                    "anthropic/claude-opus-4.5": "high",  # key has prefix, model doesn't
+                },
+            },
+        }
+        monkeypatch.setattr(tui_server, "_load_cfg", lambda: fake_cfg)
+
+        result = tui_server._load_reasoning_config()
+        assert result is not None
+        assert result["effort"] == "high"
+
+    def test_parity_with_gateway_loader(self, monkeypatch):
+        """TUI and gateway loaders return identical results for same config."""
+        import gateway.run as gateway_run
+
+        fake_cfg = {
+            "model": {"default": "openrouter/anthropic/claude-sonnet-4.6"},
+            "agent": {
+                "reasoning_effort": "low",
+                "reasoning_overrides": {
+                    "claude-sonnet-4.6": "high",
+                },
+            },
+        }
+        monkeypatch.setattr(tui_server, "_load_cfg", lambda: fake_cfg)
+        monkeypatch.setattr(gateway_run, "_load_gateway_runtime_config", lambda: fake_cfg)
+
+        tui_result = tui_server._load_reasoning_config()
+        gw_result = gateway_run.GatewayRunner._load_reasoning_config()
+        assert tui_result == gw_result
+
+    def test_global_fallback_with_yaml_false(self, monkeypatch):
+        """YAML boolean False must reach parse_reasoning_effort uncoerced.
+
+        Regression: str(... or "").strip() turned False into "", silently
+        re-enabling thinking. The raw value must pass through so
+        parse_reasoning_effort(False) returns {'enabled': False}.
+        """
+        fake_cfg = {
+            "model": {"default": "gpt-5"},
+            "agent": {
+                "reasoning_effort": False,  # YAML boolean, not string
+            },
+        }
+        monkeypatch.setattr(tui_server, "_load_cfg", lambda: fake_cfg)
+
+        result = tui_server._load_reasoning_config()
+        assert result is not None
+        assert result.get("enabled") is False
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 83c79975e2ae..db32955ddd90 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -2563,13 +2563,33 @@ def _display_mouse_tracking(display: dict) -> str:
 
 
 def _load_reasoning_config() -> dict | None:
-    from hermes_constants import parse_reasoning_effort
+    """Load reasoning effort from config.yaml, respecting per-model overrides.
 
-    # Pass the raw value through — ``or ""`` would coerce a YAML boolean
-    # False (``reasoning_effort: false``/``off``/``no``) to "", silently
-    # re-enabling thinking for users who explicitly turned it off.
+    Per-model overrides (agent.reasoning_overrides) take precedence
+    over the global value when the current model matches a key
+    (spelling-tolerant). Closes #21256.
+    """
+    from hermes_constants import parse_reasoning_effort, resolve_per_model_reasoning_effort
+
+    cfg = _load_cfg()
+
+    # Per-model override first
+    model_cfg = cfg.get("model") or {}
+    model = str(
+        (model_cfg.get("default", "") if isinstance(model_cfg, dict) else "")
+        or (model_cfg.get("model", "") if isinstance(model_cfg, dict) else "")
+        or ""
+    ).strip()
+    overrides = (cfg.get("agent") or {}).get("reasoning_overrides", {}) or {}
+    per_model = resolve_per_model_reasoning_effort(model, overrides)
+    if per_model is not None:
+        return per_model
+
+    # Global fallback — pass the raw value through; ``or ""`` would coerce
+    # a YAML boolean False (``reasoning_effort: false``/``off``/``no``) to
+    # "", silently re-enabling thinking for users who explicitly turned it off.
     return parse_reasoning_effort(
-        (_load_cfg().get("agent") or {}).get("reasoning_effort", "")
+        (cfg.get("agent") or {}).get("reasoning_effort", "")
     )
 
 
diff --git a/website/docs/user-guide/configuration.md b/website/docs/user-guide/configuration.md
index 40748ce23197..67f3a0ed5c5b 100644
--- a/website/docs/user-guide/configuration.md
+++ b/website/docs/user-guide/configuration.md
@@ -1301,6 +1301,37 @@ You can also change the reasoning effort at runtime with the `/reasoning` comman
 /reasoning hide      # Hide model thinking
 ```
 
+#### Per-Model Reasoning Overrides
+
+You can set different reasoning effort levels for different models. This is useful when you want high reasoning for complex models but medium for faster ones:
+
+```yaml
+agent:
+  reasoning_effort: "medium"       # global default
+  reasoning_overrides:
+    "openrouter/anthropic/claude-opus-4.5": "xhigh"
+    "openai/gpt-5": "low"
+    "claude-sonnet-4.6": "high"    # bare model name also works
+```
+
+The key matching is **spelling-tolerant** — any reasonable spelling will match:
+- `claude-opus-4.5`, `claude-opus-4-5`, `claude-opus.4.5` (dots and dashes are interchangeable)
+- `anthropic/claude-opus-4.5`, `openrouter/anthropic/claude-opus-4.5` (provider prefix optional)
+- Exact matches take precedence over variants
+
+:::note
+There is no `hermes config set` support for `reasoning_overrides` keys — edit the YAML file directly. This is because model names often contain dots (e.g. `claude-opus-4.5`), which conflict with the CLI's dotted-key syntax.
+:::
+
+**Resolution priority:**
+
+1. Session-scoped `/reasoning --session` override (gateway only)
+2. Per-model override from `agent.reasoning_overrides` (spelling-tolerant)
+3. Global `agent.reasoning_effort`
+4. Provider default
+
+The override applies automatically everywhere: CLI startup, messaging gateway, Desktop/TUI, cron jobs, `/model` mid-session switches, and fallback model activation.
+
 ## 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.