diff --git a/agent/anthropic_adapter.py b/agent/anthropic_adapter.py
index 740986203d..1b8e139760 100644
--- a/agent/anthropic_adapter.py
+++ b/agent/anthropic_adapter.py
@@ -20,7 +20,7 @@ from pathlib import Path
 
 from hermes_constants import get_hermes_home
 from typing import Any, Dict, List, Optional, Tuple
-from utils import normalize_proxy_env_vars
+from utils import base_url_host_matches, normalize_proxy_env_vars
 
 # NOTE: `import anthropic` is deliberately NOT at module top — the SDK pulls
 # ~220 ms of imports (anthropic.types, anthropic.lib.tools._beta_runner, etc.)
@@ -365,6 +365,61 @@ def _is_kimi_coding_endpoint(base_url: str | None) -> bool:
     return normalized.rstrip("/").lower().startswith("https://api.kimi.com/coding")
 
 
+# Model-name prefixes that identify the Kimi / Moonshot family.  Covers
+# - official slugs: ``kimi-k2.5``, ``kimi_thinking``, ``moonshot-v1-8k``
+# - common release lines: ``k1.5-...``, ``k2-thinking``, ``k25-...``, ``k2.5-...``
+# Matched case-insensitively against the post-``normalize_model_name`` form,
+# so a caller's ``provider/vendor/model`` slug is handled the same as a
+# bare name.
+_KIMI_FAMILY_MODEL_PREFIXES = (
+    "kimi-", "kimi_",
+    "moonshot-", "moonshot_",
+    "k1.", "k1-",
+    "k2.", "k2-",
+    "k25", "k2.5",
+)
+
+
+def _model_name_is_kimi_family(model: str | None) -> bool:
+    if not isinstance(model, str):
+        return False
+    m = model.strip().lower()
+    if not m:
+        return False
+    # Strip vendor prefix (e.g. ``moonshotai/kimi-k2.5`` → ``kimi-k2.5``)
+    if "/" in m:
+        m = m.rsplit("/", 1)[-1]
+    return m.startswith(_KIMI_FAMILY_MODEL_PREFIXES)
+
+
+def _is_kimi_family_endpoint(base_url: str | None, model: str | None = None) -> bool:
+    """Return True for any Kimi / Moonshot Anthropic-Messages-speaking endpoint.
+
+    Broader than ``_is_kimi_coding_endpoint`` — matches:
+
+    - Kimi's official ``/coding`` URL (legacy check, preserved)
+    - Any ``api.kimi.com`` / ``moonshot.ai`` / ``moonshot.cn`` host
+    - Custom or proxied endpoints whose *model* name is in the Kimi / Moonshot
+      family (``kimi-*``, ``moonshot-*``, ``k1.*``, ``k2.*``, …).  Users with
+      ``api_mode: anthropic_messages`` on a private gateway fronting Kimi
+      fall into this branch — the upstream still enforces Kimi's thinking
+      semantics (reasoning_content required on every replayed tool-call
+      message) regardless of the gateway's hostname.
+
+    Used to decide whether to drop Anthropic's ``thinking`` kwarg and to
+    preserve unsigned reasoning_content-derived thinking blocks on replay.
+    See hermes-agent#13848, #17057.
+    """
+    if _is_kimi_coding_endpoint(base_url):
+        return True
+    for _domain in ("api.kimi.com", "moonshot.ai", "moonshot.cn"):
+        if base_url_host_matches(base_url or "", _domain):
+            return True
+    if _model_name_is_kimi_family(model):
+        return True
+    return False
+
+
 def _requires_bearer_auth(base_url: str | None) -> bool:
     """Return True for Anthropic-compatible providers that require Bearer auth.
 
@@ -1268,6 +1323,7 @@ def _convert_content_to_anthropic(content: Any) -> Any:
 def convert_messages_to_anthropic(
     messages: List[Dict],
     base_url: str | None = None,
+    model: str | None = None,
 ) -> Tuple[Optional[Any], List[Dict]]:
     """Convert OpenAI-format messages to Anthropic format.
 
@@ -1279,6 +1335,12 @@ def convert_messages_to_anthropic(
     endpoint, all thinking block signatures are stripped.  Signatures are
     Anthropic-proprietary — third-party endpoints cannot validate them and will
     reject them with HTTP 400 "Invalid signature in thinking block".
+
+    When *model* is provided and matches the Kimi / Moonshot family (or
+    *base_url* is a Kimi / Moonshot host), unsigned thinking blocks
+    synthesised from ``reasoning_content`` are preserved on replayed
+    assistant tool-call messages — Kimi requires the field to exist, even
+    if empty.
     """
     system = None
     result = []
@@ -1507,7 +1569,7 @@ def convert_messages_to_anthropic(
     #    cache markers can interfere with signature validation.
     _THINKING_TYPES = frozenset(("thinking", "redacted_thinking"))
     _is_third_party = _is_third_party_anthropic_endpoint(base_url)
-    _is_kimi = _is_kimi_coding_endpoint(base_url)
+    _is_kimi = _is_kimi_family_endpoint(base_url, model)
 
     last_assistant_idx = None
     for i in range(len(result) - 1, -1, -1):
@@ -1630,7 +1692,9 @@ def build_anthropic_kwargs(
     Currently only supported on native Anthropic endpoints (not third-party
     compatible ones).
     """
-    system, anthropic_messages = convert_messages_to_anthropic(messages, base_url=base_url)
+    system, anthropic_messages = convert_messages_to_anthropic(
+        messages, base_url=base_url, model=model
+    )
     anthropic_tools = convert_tools_to_anthropic(tools) if tools else []
 
     model = normalize_model_name(model, preserve_dots=preserve_dots)
@@ -1736,7 +1800,7 @@ def build_anthropic_kwargs(
     # silently hides reasoning text that Hermes surfaces in its CLI. We
     # request "summarized" so the reasoning blocks stay populated — matching
     # 4.6 behavior and preserving the activity-feed UX during long tool runs.
-    _is_kimi_coding = _is_kimi_coding_endpoint(base_url)
+    _is_kimi_coding = _is_kimi_family_endpoint(base_url, model)
     if reasoning_config and isinstance(reasoning_config, dict) and not _is_kimi_coding:
         if reasoning_config.get("enabled") is not False and "haiku" not in model.lower():
             effort = str(reasoning_config.get("effort", "medium")).lower()
diff --git a/tests/agent/test_kimi_coding_anthropic_thinking.py b/tests/agent/test_kimi_coding_anthropic_thinking.py
index 706f7e0e16..89872cc2f0 100644
--- a/tests/agent/test_kimi_coding_anthropic_thinking.py
+++ b/tests/agent/test_kimi_coding_anthropic_thinking.py
@@ -94,13 +94,16 @@ class TestKimiCodingSkipsAnthropicThinking:
         )
         assert "thinking" in kwargs
 
-    def test_kimi_root_endpoint_unaffected(self) -> None:
-        """Only the /coding route is special-cased — plain api.kimi.com is not.
+    def test_kimi_root_endpoint_via_anthropic_transport_omits_thinking(self) -> None:
+        """Plain ``api.kimi.com`` hit via the Anthropic transport also omits thinking.
 
-        ``api.kimi.com`` without ``/coding`` uses the chat_completions transport
-        (see runtime_provider._detect_api_mode_for_url); build_anthropic_kwargs
-        should never see it, but if it somehow does we should not suppress
-        thinking there — that path has different semantics.
+        Auto-detection routes ``api.kimi.com/v1`` to ``chat_completions`` by
+        default, but users can explicitly configure
+        ``api_mode: anthropic_messages`` against any Kimi host.  The upstream
+        validation (reasoning_content required on replayed tool-call
+        messages) is the same regardless of URL path, so the thinking
+        suppression must apply to every Kimi host, not just ``/coding``.
+        See #17057.
         """
         from agent.anthropic_adapter import build_anthropic_kwargs
 
@@ -112,4 +115,98 @@ class TestKimiCodingSkipsAnthropicThinking:
             reasoning_config={"enabled": True, "effort": "medium"},
             base_url="https://api.kimi.com/v1",
         )
+        assert "thinking" not in kwargs
+
+    # ── #17057: custom / proxied Kimi-compatible endpoints ──────────
+    @pytest.mark.parametrize(
+        "base_url,model",
+        [
+            # Custom host with Kimi-family model — the reporter's case
+            ("http://my-kimi-proxy.internal", "kimi-2.6"),
+            ("https://llm.example.com/anthropic", "kimi-k2.5"),
+            ("https://llm.example.com/anthropic", "moonshot-v1-8k"),
+            ("https://llm.example.com/anthropic", "kimi_thinking"),
+            ("https://llm.example.com/anthropic", "moonshotai/kimi-k2.5"),
+            # Official Moonshot host (previously uncovered)
+            ("https://api.moonshot.ai/anthropic", "moonshot-v1-32k"),
+            ("https://api.moonshot.cn/anthropic", "moonshot-v1-32k"),
+        ],
+    )
+    def test_kimi_family_custom_endpoint_omits_thinking(
+        self, base_url: str, model: str
+    ) -> None:
+        """Custom / proxied Kimi endpoints must also strip Anthropic thinking."""
+        from agent.anthropic_adapter import build_anthropic_kwargs
+
+        kwargs = build_anthropic_kwargs(
+            model=model,
+            messages=[{"role": "user", "content": "hello"}],
+            tools=None,
+            max_tokens=4096,
+            reasoning_config={"enabled": True, "effort": "medium"},
+            base_url=base_url,
+        )
+        assert "thinking" not in kwargs, (
+            f"Kimi-family endpoint ({base_url}, {model}) must not receive "
+            f"Anthropic thinking — upstream validates reasoning_content on "
+            f"replayed tool-call history we don't preserve."
+        )
+        assert "output_config" not in kwargs
+
+    def test_custom_endpoint_non_kimi_model_keeps_thinking(self) -> None:
+        """Custom endpoint with a non-Kimi model must keep thinking intact.
+
+        Guards against over-broad model-family matching — only model names
+        starting with a Kimi/Moonshot prefix should trigger suppression.
+        """
+        from agent.anthropic_adapter import build_anthropic_kwargs
+
+        kwargs = build_anthropic_kwargs(
+            model="MiniMax-M2.7",
+            messages=[{"role": "user", "content": "hello"}],
+            tools=None,
+            max_tokens=4096,
+            reasoning_config={"enabled": True, "effort": "medium"},
+            base_url="https://my-llm-proxy.example.com/anthropic",
+        )
         assert "thinking" in kwargs
+        assert kwargs["thinking"]["type"] == "enabled"
+
+    def test_kimi_family_replay_preserves_unsigned_thinking(self) -> None:
+        """On a custom Kimi endpoint, unsigned reasoning_content thinking
+        blocks must survive the third-party signature-stripping pass so
+        the upstream's message-history validation passes.
+        """
+        from agent.anthropic_adapter import convert_messages_to_anthropic
+
+        messages = [
+            {"role": "user", "content": "hi"},
+            {
+                "role": "assistant",
+                "reasoning_content": "planning the tool call",
+                "tool_calls": [
+                    {
+                        "id": "call_1",
+                        "type": "function",
+                        "function": {"name": "skill_view", "arguments": "{}"},
+                    }
+                ],
+            },
+            {"role": "tool", "tool_call_id": "call_1", "content": "ok"},
+        ]
+        _, converted = convert_messages_to_anthropic(
+            messages,
+            base_url="http://my-kimi-proxy.internal",
+            model="kimi-2.6",
+        )
+        # The assistant message still carries the unsigned thinking block
+        # synthesised from reasoning_content (required by Kimi's history
+        # validation).  A plain third-party endpoint would have stripped it.
+        assistant_msg = next(m for m in converted if m["role"] == "assistant")
+        assistant_blocks = assistant_msg["content"]
+        thinking_blocks = [
+            b for b in assistant_blocks
+            if isinstance(b, dict) and b.get("type") == "thinking"
+        ]
+        assert len(thinking_blocks) == 1
+        assert thinking_blocks[0]["thinking"] == "planning the tool call"