diff --git a/src/plyngent/config/__init__.py b/src/plyngent/config/__init__.py
index 9df1dbd..526e40d 100644
--- a/src/plyngent/config/__init__.py
+++ b/src/plyngent/config/__init__.py
@@ -21,10 +21,13 @@ from .models import OpenAICompatibleProvider as OpenAICompatibleProvider
 from .models import OpenAIProvider as OpenAIProvider
 from .models import PluginsConfig as PluginsConfig
 from .models import ProviderConfig as ProviderConfig
+from .models import ReasoningEffortConfig as ReasoningEffortConfig
 from .models import SkillDiscoverySource as SkillDiscoverySource
 from .models import SkillsConfig as SkillsConfig
 from .models import compose_agent_system_content as compose_agent_system_content
 from .path import get_default_path as _get_default_path
+from .reasoning import ReasoningConfig as ReasoningConfig
+from .reasoning import resolve_reasoning as resolve_reasoning
 from .routing import EffectiveProvider as EffectiveProvider
 from .routing import ProviderPreset as ProviderPreset
 from .routing import default_url_for_preset as default_url_for_preset
diff --git a/src/plyngent/config/models.py b/src/plyngent/config/models.py
index bb599a9..a93d887 100644
--- a/src/plyngent/config/models.py
+++ b/src/plyngent/config/models.py
@@ -13,6 +13,14 @@ type DeepSeekConvention = Literal["", "openai", "anthropic", "responses"]
 # Static directory pre-allow mode for ``[agent].allow_paths`` (path → mode).
 type AllowPathMode = Literal["read", "write", "exec"]
 
+# Thinking strength, normalized across API surfaces (``reasoning_effort`` on
+# ``[agent]``, a provider, or a single model; the most specific one wins).
+# "" = send nothing and let the provider pick its own default.
+# Mapped per surface by ``config.reasoning``: chat completions / Responses send
+# ``reasoning_effort`` / ``reasoning.effort`` (``max`` is DeepSeek-only and
+# clamps to ``xhigh`` elsewhere), Anthropic maps it onto ``thinking``.
+type ReasoningEffortConfig = Literal["", "none", "minimal", "low", "medium", "high", "xhigh", "max"]
+
 # Built-in skill discovery sources (``[skills].discover``): our own user config
 # directory, and the skill directories other harnesses install into.
 type SkillDiscoverySource = Literal["plyngent", "claude"]
@@ -150,6 +158,14 @@ class AgentConfig(Struct, omit_defaults=True):
     compact_user_prefix: str = ""
     compact_seed_text: str = ""
 
+    # Thinking strength for every request (a provider or single model may
+    # override either value; the most specific one wins).
+    # reasoning_effort: "" | none | minimal | low | medium | high | xhigh | max.
+    # thinking_budget_tokens: explicit Anthropic ``thinking`` budget (0 = derive
+    # it from ``reasoning_effort``). See config/reasoning.py.
+    reasoning_effort: ReasoningEffortConfig = ""
+    thinking_budget_tokens: int = 0
+
 
 class PluginsConfig(Struct, omit_defaults=True):
     """Third-party plugins (not tool-specific config).
@@ -268,6 +284,9 @@ class ModelConfig(Struct, omit_defaults=True):
     url: str = ""
     # DeepSeek API surface override ("" = inherit provider convention).
     convention: DeepSeekConvention = ""
+    # Thinking strength for this model only ("" / 0 = inherit the provider).
+    reasoning_effort: ReasoningEffortConfig = ""
+    thinking_budget_tokens: int = 0
 
 
 class HttpTimeoutConfig(Struct, omit_defaults=True):
@@ -299,6 +318,9 @@ class ProviderConfig(Struct, tag_field="preset", omit_defaults=True):
     models: dict[str, ModelConfig] = field(default_factory=dict)
     # float = single timeout for the session; table = connect/read split; omit = defaults.
     timeout: float | HttpTimeoutConfig | None = None
+    # Thinking strength for every model of this provider ("" / 0 = inherit [agent]).
+    reasoning_effort: ReasoningEffortConfig = ""
+    thinking_budget_tokens: int = 0
 
 
 def _default_openai_models() -> dict[str, ModelConfig]:
diff --git a/src/plyngent/config/reasoning.py b/src/plyngent/config/reasoning.py
new file mode 100644
index 0000000..c9df677
--- /dev/null
+++ b/src/plyngent/config/reasoning.py
@@ -0,0 +1,80 @@
+"""Thinking-strength resolution across config layers and API surfaces.
+
+``reasoning_effort`` (and the optional Anthropic ``thinking_budget_tokens``) may
+be set on ``[agent]``, on a provider, or on a single model. This module merges
+the layers — the most specific one wins, per field — and normalizes the result
+for the API surface the provider actually talks to, so the agent loop and the
+provider bridges receive one value with a single meaning:
+
+* ``""`` — send nothing; the provider applies its own default.
+* chat completions / Responses — ``reasoning_effort`` / ``reasoning.effort``.
+* Anthropic — ``thinking`` (an effort level has no wire form there).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING
+
+from .routing import model_config_for, resolve_effective_provider
+
+if TYPE_CHECKING:
+    from .models import AgentConfig, Provider, ReasoningEffortConfig
+
+# DeepSeek's own ``reasoning_effort`` accepts "max"; OpenAI and Anthropic do not,
+# so anywhere else it clamps down to the highest level they do understand.
+_DEEPSEEK_CHAT_CONVENTIONS = frozenset({"", "openai"})
+
+
+@dataclass(frozen=True, slots=True)
+class ReasoningConfig:
+    """Merged thinking settings for one provider + model."""
+
+    effort: ReasoningEffortConfig = ""
+    # Explicit Anthropic ``thinking`` budget; 0 = derive it from ``effort``.
+    thinking_budget_tokens: int = 0
+
+
+def _clamp_effort(effort: ReasoningEffortConfig, *, preset: str, convention: str) -> ReasoningEffortConfig:
+    """Keep ``max`` only on the DeepSeek chat surface that defines it."""
+    if effort != "max":
+        return effort
+    if preset == "deepseek" and convention in _DEEPSEEK_CHAT_CONVENTIONS:
+        return effort
+    return "xhigh"
+
+
+def resolve_reasoning(
+    agent: AgentConfig | None,
+    provider: Provider,
+    model: str | None,
+) -> ReasoningConfig:
+    """Merge ``[agent]`` < provider < model thinking settings for *model*.
+
+    *agent* is ``None`` for callers that only know the provider (config tools,
+    tests); the model layer is the provider's entry for *model*, if any. Each
+    field falls back on its own, so a model may inherit only the effort (or only
+    the budget) from above.
+    """
+    effective = resolve_effective_provider(provider, model=model)
+    model_config = model_config_for(provider, model)
+
+    effort: ReasoningEffortConfig = ""
+    for layer in (model_config, provider, agent):
+        if layer is not None and layer.reasoning_effort:
+            effort = layer.reasoning_effort
+            break
+
+    budget = 0
+    for layer in (model_config, provider, agent):
+        if layer is not None and layer.thinking_budget_tokens > 0:
+            budget = layer.thinking_budget_tokens
+            break
+
+    return ReasoningConfig(
+        effort=_clamp_effort(effort, preset=effective.preset, convention=effective.convention),
+        thinking_budget_tokens=budget,
+    )
+
+
+__all__ = ["ReasoningConfig", "resolve_reasoning"]
diff --git a/tests/test_config/test_agent_section.py b/tests/test_config/test_agent_section.py
index 1237f58..05ba9ba 100644
--- a/tests/test_config/test_agent_section.py
+++ b/tests/test_config/test_agent_section.py
@@ -29,6 +29,8 @@ def test_agent_section_defaults(tmp_path: Path) -> None:
     assert store.agent_config.allow_paths == {}
     assert store.agent_config.auto_continue_limits is False
     assert store.agent_config.max_context_tokens == 200_000
+    assert store.agent_config.reasoning_effort == ""
+    assert store.agent_config.thinking_budget_tokens == 0
     assert store.plugins_config.enable == []
     assert store.plugins_config.disable == []
     assert store.networking_config.ssrf_assume_public_cidrs == []
diff --git a/tests/test_config/test_config.py b/tests/test_config/test_config.py
index 942be5c..97c886b 100644
--- a/tests/test_config/test_config.py
+++ b/tests/test_config/test_config.py
@@ -299,6 +299,70 @@ def test_read_bad_config() -> None:
     assert isinstance(config.bad_providers, Mapping)
 
 
+def test_reasoning_effort_from_toml(tmp_path: Path) -> None:
+    path = tmp_path / "reasoning.toml"
+    _ = path.write_text(
+        """
+[agent]
+reasoning_effort = "low"
+thinking_budget_tokens = 4000
+
+[providers.ds]
+preset = "deepseek"
+access_key_or_token = "sk-test"
+reasoning_effort = "high"
+
+[providers.ds.models]
+"deepseek-v4-pro" = { text = true, reasoning_effort = "max", thinking_budget_tokens = 32000 }
+"deepseek-v4-flash" = { text = true }
+""",
+        encoding="utf-8",
+    )
+    config = plyngent.config.load(path)
+    agent_cfg = config.agent_config
+    assert agent_cfg.reasoning_effort == "low"
+    assert agent_cfg.thinking_budget_tokens == 4000
+    provider = config.providers["ds"]
+    assert provider.reasoning_effort == "high"
+    assert provider.thinking_budget_tokens == 0
+    assert provider.models["deepseek-v4-pro"].reasoning_effort == "max"
+    assert provider.models["deepseek-v4-pro"].thinking_budget_tokens == 32000
+    assert provider.models["deepseek-v4-flash"].reasoning_effort == ""
+    assert provider.models["deepseek-v4-flash"].thinking_budget_tokens == 0
+
+
+def test_reasoning_effort_defaults_are_unset(tmp_path: Path) -> None:
+    path = tmp_path / "reasoning-default.toml"
+    _ = path.write_text(
+        """
+[providers.ds]
+preset = "deepseek"
+access_key_or_token = "sk-test"
+""",
+        encoding="utf-8",
+    )
+    config = plyngent.config.load(path)
+    assert config.agent_config.reasoning_effort == ""
+    assert config.agent_config.thinking_budget_tokens == 0
+    assert config.providers["ds"].reasoning_effort == ""
+
+
+def test_reasoning_effort_invalid_is_bad_provider(tmp_path: Path) -> None:
+    path = tmp_path / "reasoning-bad.toml"
+    _ = path.write_text(
+        """
+[providers.ds]
+preset = "deepseek"
+access_key_or_token = "sk-test"
+reasoning_effort = "highest"
+""",
+        encoding="utf-8",
+    )
+    config = plyngent.config.load(path)
+    assert "ds" not in config.providers
+    assert "ds" in config.bad_providers
+
+
 def test_provider_with_empty_models_is_recoverable(tmp_path: Path) -> None:
     path = tmp_path / "empty-models.toml"
     _ = path.write_text(
diff --git a/tests/test_config/test_reasoning.py b/tests/test_config/test_reasoning.py
new file mode 100644
index 0000000..eaa8baf
--- /dev/null
+++ b/tests/test_config/test_reasoning.py
@@ -0,0 +1,100 @@
+"""Tests for thinking-strength resolution across config layers and surfaces."""
+
+from __future__ import annotations
+
+from plyngent.config.models import (
+    AgentConfig,
+    AnthropicProvider,
+    DeepseekProvider,
+    ModelConfig,
+    OpenAICompatibleProvider,
+    OpenAIProvider,
+)
+from plyngent.config.reasoning import resolve_reasoning
+
+
+def _compat() -> OpenAICompatibleProvider:
+    return OpenAICompatibleProvider(access_key_or_token="sk-test", url="https://example.com/v1")
+
+
+def test_agent_layer_only() -> None:
+    reasoning = resolve_reasoning(
+        AgentConfig(reasoning_effort="high", thinking_budget_tokens=9000),
+        _compat(),
+        "gpt-4o-mini",
+    )
+    assert reasoning.effort == "high"
+    assert reasoning.thinking_budget_tokens == 9000
+
+
+def test_provider_overrides_agent_and_model_overrides_provider() -> None:
+    provider = OpenAICompatibleProvider(
+        access_key_or_token="sk-test",
+        url="https://example.com/v1",
+        reasoning_effort="low",
+        models={"gpt-4o-mini": ModelConfig(reasoning_effort="xhigh")},
+    )
+    agent = AgentConfig(reasoning_effort="minimal")
+    assert resolve_reasoning(agent, provider, "gpt-4o-mini").effort == "xhigh"
+    assert resolve_reasoning(agent, provider, "other-model").effort == "low"
+    assert resolve_reasoning(agent, provider, None).effort == "low"
+
+
+def test_fields_fall_back_independently() -> None:
+    provider = OpenAICompatibleProvider(
+        access_key_or_token="sk-test",
+        url="https://example.com/v1",
+        reasoning_effort="high",
+        thinking_budget_tokens=20000,
+        models={"gpt-4o-mini": ModelConfig(thinking_budget_tokens=4000)},
+    )
+    reasoning = resolve_reasoning(AgentConfig(reasoning_effort="low"), provider, "gpt-4o-mini")
+    # Model sets the budget only → the effort still comes from the provider.
+    assert reasoning.effort == "high"
+    assert reasoning.thinking_budget_tokens == 4000
+
+
+def test_agent_layer_optional() -> None:
+    provider = OpenAICompatibleProvider(
+        access_key_or_token="sk-test",
+        url="https://example.com/v1",
+        reasoning_effort="medium",
+    )
+    assert resolve_reasoning(None, provider, "gpt-4o-mini").effort == "medium"
+
+
+def test_unset_layers_stay_unspecified() -> None:
+    reasoning = resolve_reasoning(None, _compat(), "gpt-4o-mini")
+    assert reasoning.effort == ""
+    assert reasoning.thinking_budget_tokens == 0
+
+
+def test_non_positive_budget_is_ignored() -> None:
+    provider = OpenAICompatibleProvider(
+        access_key_or_token="sk-test",
+        url="https://example.com/v1",
+        thinking_budget_tokens=0,
+    )
+    resolved = resolve_reasoning(AgentConfig(thinking_budget_tokens=-5), provider, "gpt-4o-mini")
+    assert resolved.thinking_budget_tokens == 0
+
+
+def test_max_survives_only_on_deepseek_chat() -> None:
+    chat = DeepseekProvider(access_key_or_token="sk-test", reasoning_effort="max")
+    assert resolve_reasoning(None, chat, "deepseek-v4-pro").effort == "max"
+
+    responses = DeepseekProvider(access_key_or_token="sk-test", convention="responses", reasoning_effort="max")
+    assert resolve_reasoning(None, responses, "deepseek-v4-pro").effort == "xhigh"
+
+    anthropic = AnthropicProvider(access_key_or_token="sk-test", reasoning_effort="max")
+    assert resolve_reasoning(None, anthropic, "claude-test").effort == "xhigh"
+
+    openai = OpenAIProvider(access_key_or_token="sk-test", reasoning_effort="max")
+    assert resolve_reasoning(None, openai, "gpt-5.4").effort == "xhigh"
+
+
+def test_effort_levels_pass_through_unchanged() -> None:
+    provider = _compat()
+    for effort in ("none", "minimal", "low", "medium", "high", "xhigh"):
+        resolved = resolve_reasoning(AgentConfig(reasoning_effort=effort), provider, "gpt-4o-mini")
+        assert resolved.effort == effort