diff --git a/run_agent.py b/run_agent.py
index 512ef1cce..34ab7f450 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -2005,6 +2005,22 @@ class AIAgent:
         self._fallback_activated = False
         self._fallback_index = 0
 
+        # When the user deliberately swaps primary providers (e.g. openrouter
+        # → anthropic), drop any fallback entries that target the OLD primary
+        # or the NEW one.  The chain was seeded from config at agent init for
+        # the original provider — without pruning, a failed turn on the new
+        # primary silently re-activates the provider the user just rejected,
+        # which is exactly what was reported during TUI v2 blitz testing
+        # ("switched to anthropic, tui keeps trying openrouter").
+        old_norm = (old_provider or "").strip().lower()
+        new_norm = (new_provider or "").strip().lower()
+        if old_norm and new_norm and old_norm != new_norm:
+            self._fallback_chain = [
+                entry for entry in self._fallback_chain
+                if (entry.get("provider") or "").strip().lower() not in {old_norm, new_norm}
+            ]
+            self._fallback_model = self._fallback_chain[0] if self._fallback_chain else None
+
         logging.info(
             "Model switched in-place: %s (%s) -> %s (%s)",
             old_model, old_provider, new_model, new_provider,
diff --git a/tests/run_agent/test_switch_model_fallback_prune.py b/tests/run_agent/test_switch_model_fallback_prune.py
new file mode 100644
index 000000000..99af3579f
--- /dev/null
+++ b/tests/run_agent/test_switch_model_fallback_prune.py
@@ -0,0 +1,93 @@
+"""Regression test for TUI v2 blitz bug: explicit /model --provider switch
+silently fell back to the old primary provider on the next turn because the
+fallback chain — seeded from config at agent __init__ — kept entries for the
+provider the user just moved away from.
+
+Reported: "switched from openrouter provider to anthropic api key via hermes
+model and the tui keeps trying openrouter".
+"""
+
+from unittest.mock import MagicMock, patch
+
+from run_agent import AIAgent
+
+
+def _make_agent(chain):
+    agent = AIAgent.__new__(AIAgent)
+
+    agent.provider = "openrouter"
+    agent.model = "x-ai/grok-4"
+    agent.base_url = "https://openrouter.ai/api/v1"
+    agent.api_key = "or-key"
+    agent.api_mode = "chat_completions"
+    agent.client = MagicMock()
+    agent._client_kwargs = {"api_key": "or-key", "base_url": "https://openrouter.ai/api/v1"}
+    agent.context_compressor = None
+    agent._anthropic_api_key = ""
+    agent._anthropic_base_url = None
+    agent._anthropic_client = None
+    agent._is_anthropic_oauth = False
+    agent._cached_system_prompt = "cached"
+    agent._primary_runtime = {}
+    agent._fallback_activated = False
+    agent._fallback_index = 0
+    agent._fallback_chain = list(chain)
+    agent._fallback_model = chain[0] if chain else None
+
+    return agent
+
+
+def _switch_to_anthropic(agent):
+    with (
+        patch("agent.anthropic_adapter.build_anthropic_client", return_value=MagicMock()),
+        patch("agent.anthropic_adapter.resolve_anthropic_token", return_value="sk-ant-xyz"),
+        patch("agent.anthropic_adapter._is_oauth_token", return_value=False),
+        patch("hermes_cli.timeouts.get_provider_request_timeout", return_value=None),
+    ):
+        agent.switch_model(
+            new_model="claude-sonnet-4-5",
+            new_provider="anthropic",
+            api_key="sk-ant-xyz",
+            base_url="https://api.anthropic.com",
+            api_mode="anthropic_messages",
+        )
+
+
+def test_switch_drops_old_primary_from_fallback_chain():
+    agent = _make_agent([
+        {"provider": "openrouter", "model": "x-ai/grok-4"},
+        {"provider": "nous", "model": "hermes-4"},
+    ])
+
+    _switch_to_anthropic(agent)
+
+    providers = [entry["provider"] for entry in agent._fallback_chain]
+
+    assert "openrouter" not in providers, "old primary must be pruned"
+    assert "anthropic" not in providers, "new primary is redundant in the chain"
+    assert providers == ["nous"]
+    assert agent._fallback_model == {"provider": "nous", "model": "hermes-4"}
+
+
+def test_switch_with_empty_chain_stays_empty():
+    agent = _make_agent([])
+
+    _switch_to_anthropic(agent)
+
+    assert agent._fallback_chain == []
+    assert agent._fallback_model is None
+
+
+def test_switch_within_same_provider_preserves_chain():
+    chain = [{"provider": "openrouter", "model": "x-ai/grok-4"}]
+    agent = _make_agent(chain)
+
+    with patch("hermes_cli.timeouts.get_provider_request_timeout", return_value=None):
+        agent.switch_model(
+            new_model="openai/gpt-5",
+            new_provider="openrouter",
+            api_key="or-key",
+            base_url="https://openrouter.ai/api/v1",
+        )
+
+    assert agent._fallback_chain == chain
diff --git a/tests/test_tui_gateway_server.py b/tests/test_tui_gateway_server.py
index 3909c3ed8..7a7f63284 100644
--- a/tests/test_tui_gateway_server.py
+++ b/tests/test_tui_gateway_server.py
@@ -1,4 +1,5 @@
 import json
+import os
 import sys
 import threading
 import time
@@ -230,6 +231,48 @@ def test_config_set_model_global_persists(monkeypatch):
     assert saved["model"]["base_url"] == "https://api.anthropic.com"
 
 
+def test_config_set_model_syncs_inference_provider_env(monkeypatch):
+    """After an explicit provider switch, HERMES_INFERENCE_PROVIDER must
+    reflect the user's choice so ambient re-resolution (credential pool
+    refresh, aux clients) picks up the new provider instead of the original
+    one persisted in config or shell env.
+
+    Regression: a TUI user switched openrouter → anthropic and the TUI kept
+    trying openrouter because the env-var-backed resolvers still saw the old
+    provider.
+    """
+    class _Agent:
+        provider = "openrouter"
+        model = "old/model"
+        base_url = ""
+        api_key = "sk-or"
+
+        def switch_model(self, **_kwargs):
+            return None
+
+    result = types.SimpleNamespace(
+        success=True,
+        new_model="claude-sonnet-4.6",
+        target_provider="anthropic",
+        api_key="sk-ant",
+        base_url="https://api.anthropic.com",
+        api_mode="anthropic_messages",
+        warning_message="",
+    )
+
+    server._sessions["sid"] = _session(agent=_Agent())
+    monkeypatch.setenv("HERMES_INFERENCE_PROVIDER", "openrouter")
+    monkeypatch.setattr("hermes_cli.model_switch.switch_model", lambda **_kwargs: result)
+    monkeypatch.setattr(server, "_restart_slash_worker", lambda session: None)
+    monkeypatch.setattr(server, "_emit", lambda *args, **kwargs: None)
+
+    server.handle_request(
+        {"id": "1", "method": "config.set", "params": {"session_id": "sid", "key": "model", "value": "claude-sonnet-4.6 --provider anthropic"}}
+    )
+
+    assert os.environ["HERMES_INFERENCE_PROVIDER"] == "anthropic"
+
+
 def test_config_set_personality_rejects_unknown_name(monkeypatch):
     monkeypatch.setattr(server, "_available_personalities", lambda cfg=None: {"helpful": "You are helpful."})
     resp = server.handle_request(
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 1acdf295e..73bc39ffb 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -538,6 +538,12 @@ def _apply_model_switch(sid: str, session: dict, raw_input: str) -> dict:
         _emit("session.info", sid, _session_info(agent))
 
     os.environ["HERMES_MODEL"] = result.new_model
+    # Keep the process-level provider env var in sync with the user's explicit
+    # choice so any ambient re-resolution (credential pool refresh, compressor
+    # rebuild, aux clients) resolves to the new provider instead of the
+    # original one persisted in config or env.
+    if result.target_provider:
+        os.environ["HERMES_INFERENCE_PROVIDER"] = result.target_provider
     if persist_global:
         _persist_model_switch(result)
     return {"value": result.new_model, "warning": result.warning_message or ""}